Considering an idea of F. Arago in 1853 regarding light dispersion through the light ether in the interstellar space, this paper presents a new idea on an alternative interpretation of the cosmological red shift of the galaxies in the universe. The model is based on an analogy with the temporal material dispersion that occurs with light in the optical fiber core. Since intergalactic space is transparent, according to the model, this phenomenon is related to the gravitational potential existing in the whole space. Thus, it is possible to find a new interpretation to Hubble's constant. In space, light undergoes a dispersion process in its path, which is interpreted by a red shift equation of the type Δz = HL, since H = (d2n/dλ2 Δv Δλ), where H means the Hubble constant, n is the refractive index of the intergalactic space, Δλ is the spectral width of the extragalactic source, and Δv is the variation of the speed of light caused by the gravitational potential. We observe that this "constant" is governed by three new parameters. Light traveling the intergalactic space undergoes red shift due to this mechanism, while light amplitude decreases with time, and the wavelength always increases, thus producing the same type of behavior given by Hubble's Law. It can be demonstrated that the dark matter phenomenon is produced by the apparent speed of light of the stars on the periphery of the galaxies, without the existence of dark energy. Based on this new idea, the model of the universe is static, lacking expansion. Other phenomena may be interpreted based on this new model of the universe. We have what we call temporal gravitational dispersion of light in space produced by the variations of the speed of light, due to the presence of the gravitational potential in the whole space.
This study aims to build a prototype of a new device for measuring by optics, the level of liquids or liquefied gases in tanks without the use of moving parts for general applications, stationary or not, industrial and chemical vehicles. There are a lot of optical devices for measuring liquid level and various settings and runs, some devices with buildings and sophisticated technologies, complicated and more simple, but none of these devices has the configuration (provision and operation), for measuring by optical means, the level of liquids in tanks and reservoirs. That is a simple, efficient and cost effective device.
A test method was developed to find the ideal optical material that supports the chemical reaction of some fuels. Optical plastics and resin were submerged for long periods of time in reservoirs of ethanol, gasoline, Diesel and biodiesel. The dimensional change and weight change of the submerged samples was measured. A special resin successfully supported the chemical attack of fuels. Samples of acrylic polymer and polycarbonate were used as type of optical plastic.
In the present paper, optical absorption and emission spectra and luminescence decay lifetimes of different concentrations, 0.1, 0.3, 0.5, 0.7 and 1.0 mol% of Er3+ and 0.1Er3+/0.5Yb3+ co-doped tellurite glasses (TeO2-Bi2O3-ZnONb2O5) were reported. Judd-Ofelt intensity parameters were determined and used to calculate spontaneous radiative transition probabilities (Arad), radiative lifetimes (τR), branching ratios (β) and stimulated emission cross-sections (σP) for certain emission transitions. NIR emission at 1.5μm and up-conversion spectra of Er3+ and Er3+/Yb3+ co-doped tellurite glasses were measured under excitation wavelength of 980 nm. The absorption, emission and gain cross-sections for 4I13/2→4I15/2 transition of Er3+ are determined. The peak emission cross-section of this transition is found to be higher (9.95×10-21 cm2) for 0.1 mol% of Er3+ and lower (6.81×10-21 cm2) for 1.0 mol% of Er3+ doped tellurite glasses, which is comparable to other oxide glasses. The larger peak emission cross-section for lower concentration of Er3+ is due to the high refractive index of glass matrix (2.1547), relation established from Judd-Ofelt theory. The observed full-widths at half maxima (FWHM) for lower and higher concentrations of Er3+ are 64nm and 96 nm respectively. The larger values of FWHM and peak emission cross-sections are potentially useful for optical amplification processes in the design of Erbium doped fiber amplifiers (EDFs). Under 980 nm excitation three strong up-conversion bands were observed at 530nm, 546nm and 665nm. The pump power dependent intensities and mechanisms involved in the up-conversion process have been studied. The luminescence decay profiles for 4I13/2 level were reported for all glass matrices.
Several papers were reported on spectroscopic properties of rare earth doped different host glasses. A complete knowledge of fluorescence properties of rare earth ions in laser materials is necessary to achieve efficient, compact and cheap sources of laser radiation for NIR and mid-IR region. Tellurite glasses are potentially useful for generation of NIR and mid-IR laser radiation due to its special features such as lowest phonon energy (750 cm-1) among oxide glasses, reasonably wide transmission region (0.35 - 5μm), good glass stability, good rare earth ion solubility, high linear and non-linear refractive index. In the present work, authors prepared Ho3+ and Tm3+ singly doped and Ho3+/Tm3+ co-doped tellurite glasses using conventional melt-quenching method. Spectroscopic measurements and analysis of energy transfer process in Ho3+, Tm3+ and Ho3+ /Tm3+ co-doped glasses pumped with 785nm and 451 nm excitation wavelengths have been performed. There are some spectroscopic properties which are important in understanding and modeling of rare earth doped laser materials. Using Judd-Ofelt theory, radiative transition rates (Arad), radiative lifetimes (τR) and branching ratios (β) were estimated for certain excited states of Ho3+ and Tm3+ doped tellurite glasses. The emission cross-sections and gain coefficients have been determined from the absorption spectra of Ho3+ and Tm3+ ions in tellurite glasses. The energy transfer process such as ion cross-relaxation, Tm3+-Ho3+ energy transfer and energy transfer upconversion were studied and identified to specific candidate for laser operation.
Thulium doped Samarium codoped tellurite-tungstate glasses were produced. Luminescence properties in the infrared region were investigated looking to observe improved properties for S-band amplification in the co doped samples. Thulium is well-known by the 3H4-3F4 radiative transition emitting around ~1.47μm, which is a self-terminating transition in tellurite hosts due the longer lifetime of the lower level in relation to the upper level of this transition. Analysis of absorption and emission spectra showed that we could quench the 3F4 level significantly, what improved the intensity of the emission at 1.49μm. However, the state 3H4 were also quenched due the cross relaxation process due the absorption bands of Sm3+ around 1.5μm.
Tellurite glasses following the molar concentration 71.5% TeO2, 22.5% WO3, 5% Na2O and 1.5% Nb2O5 have been investigated. Samples doped with Tm2O3, Pr2O3, Yb2O3 or Bi2O3 were fabricated by the conventional melt quenching process. Rare-earth (RE) 3+ ions have well defined emission bands. On the other hand, Bismuth emission in the infrared region have been found in some glasses and even that emission laser have been already obtained, the mechanism behind its luminescence is still misunderstood[1]. The Bismuth emission is sometimes referred as a “superbroadband” emission around 1.3um, which is very promising for an optical amplifier, but, to the best of our knowledge a bismuth based optical amplifier have not been produced yet. Our purpose is to investigate the mechanism behind this misunderstood “superbroadband” luminescence, and compare it with the rare-earths properties in the same range. The characterization consists in measurements of optical absorption spectra, optical emission spectra and life-time decay. Differential thermal analysis (DTA) was also performed, to identify changes in Tg and Tx as function of the doping concentration, which is important to the drawing process of a fiber.
KEYWORDS: Optical fibers, Signal attenuation, Silica, Glasses, Dispersion, Supercontinuum generation, Fiber to the x, Fabrication, Nonlinear optics, Single mode fibers
Conventional core/clad optical fibers composed of all-solid silica material were fabricated using the "stack and draw"
technique. The optical fiber consists of Ge-doped silica glass in the core and un-doped silica glass in the clad. The optical
attenuation and the chromatic dispersion spectra of these optical fibers, with their external diameters of 212, 176, 150
and 125 μm, were characterized by using a PK2500 and a PK2800 instrument respectively. The attenuation of these
optical fibers, at 1550 nm, was approximately 5 dB/km and the zero-dispersion-wavelength range from 1350 to 1370 nm.
On the other hand, bend loss spectra of these fibers were characterized by using small bend diameter rods (bend
diameters from 2.5 to 10 mm). The bend loss spectra show that these all-solid optical fibers are almost insensitive to
bend effect. In addition we explore the nonlinear properties of these fibers to investigate the potential for supercontinuum
generation.
Optical results concerning the generation of laser and optical gain by using an Er3+-doped tellurite
micro-structured fiber are reported for the first time. For this purpose a scheme that consist of two 980 nm
diode pump lasers (simultaneously in the co-propagating and the counter-propagating directions) and short
Er3+-doped tellurite micro-structured fibers (fabricated by using the stack-and-draw technique and a soft glass
drawing tower) was used. The laser produced here was obtained within the range 1530 to 1565 nm, and the
maximum optical gain obtained was higher than 8 dB.
We report the fabrication of PbTe quantum dots grown under inert gas (Ar and He) atmosphere by
pulsed laser deposition using the second harmonic of a Q-Switched Quantel Nd:YAG laser. For
characterization, samples were prepared onto a 40Å carbon film deposited on a copper grid. The
influence of background pressure, and number of laser pulses on the size distribution of the PbTe
nanoparticles was investigated by transmission electron microscopy using a 200 kV TECNAI G2
F20 electron microscope with 0.27 nm point resolution. The size distribution was obtained by
manually outlining the particles from several dozens of low- and high-resolution TEM images. Once
digitized and saved in a proper format, the image was processed using the J-image software.
Characterizations reveal an increase of the nanoparticle size both with the amount of material
deposited (number of laser pulses) and the background pressure. Furthermore, measurements reveal
a narrower nanoparticle size distribution by increasing the number of laser pulses or by decreasing
the background pressure. HRTEM studies of the influence of different ambient gases on the
structural properties of the PbTe nanoparticles are being conducted.
In this work we present results of physical and optical properties of Er3+-Yb3+ co-doped tellurite glasses and fibers. The
Double Clad Tellurite Fibers (DCTFs) are based on glasses with the composition: TeO2-WO3-Nb2O5-Na2O-Al2O3-Er2O3-Yb2O3. The DCTFs were fabricated by using the rod-in-tube technique and a Heathway drawing tower. The optical
absorption spectra (ranging from 350 to 1750 nm) of these fibers were measured using an Optical Spectrum Analyzer
(OSA). The emission spectra, around 1550 nm band, of these fibers (lengths varying from 1 to 60 cm) were obtained by
using a 980nm diode laser pump. The optimal Amplified Spontaneous Emission (ASE) spectra were observed for fiber
lengths ranging from 2 to 6 cm. The Er 3+/Yb3+ co-doped DCTFs show an efficient up-conversion process in comparison
with the Er3+-doped DCTF.
In this work we show results of controlled tapered fibers using a Vytran instrument. The tapered silica
fibers were produced by pulling a 50μm length by heating time. The minimum taper diameter was around 3μm and
the maximum taper length was around 600μm. The evanescent field effect, in the near infra red (NIR) region, was
observed to the tapers with diameter inferior to 15μm. These
micro-size tapers no modify the waveguide dispersion
spectra. This device could be used to splice a conventional fiber to photonic crystal fibers and also as liquid and gas
sensors In this work is reported a fiber optic sensor in the form of taper using the concept of the evanescent field. We
show the sensor sensitivity using different liquid materials.
In this work, we present results of broadband emissions ranging from 800 to 1500 nm
generated by using Photonic Crystal Fibres (PCFs) made from borosilicate glasses. The borosilicate
PCFs, fabricated by the Stack-and-Draw technique, consist of five hollow ring periods around the solid
core. The solid core is based on the lead-doped borosilicate glass. The PCFs with their external
diameters ranging from about 3.8 to 6 microns were excited with a commercial pulsed diode laser
(wavelength at 1065 nm, Power <100mW). The PCF length used to generate broadband emissions was
less than a meter. The Optical Attenuation of these PCFs was measured via the Cut-Back method and
their Dispersion Spectra were calculated by using the Finite Element Method (FEM) and the scanning
electronic microscope images. Finally, we believe that short borosilicate PCFs with lead-doped cores
(related to high non-linear properties) may be used in broadband emissions, supercontinuum
generations or other non-linear applications.
In this work we present bend loss characteristics of silica Photonic Crystal
Fibers (PCFs) in the VIS-NIR-IR region. The PCFs made using the Stack-and-
Draw technique consist of triangular and rectangular hollow lattices. The bend
loss dependency of these PCFs was characterized by using an optical spectrum
analyzer (OSA) and a white light source. The optical transmittance spectra were
measured for different bend radius. These PCFs are sensitive to bending losses in
the VIS-NIR region, but insensitive in the IR region. These PCFs may be used to
bend sensors or optical filters.
The fabrication of small-core photonic crystal fibers and preliminary supercontinuum generation
characterization are reported. In such non-linear experiments fs pulses from a Ti:Sapphire laser were coupled in
the fiber core and the generated spectra recorded.
In this work, we report results of lead sulfide (PbS) quantum dots (QDs) luminescence spectra evolution during
the QDs spread process around the core of silica microstructured optical fibers (MOFs). These QDs are excited,
via evanescent field effect, with a 532nm or 785nm laser guided by the MOF cores. The PbS-core QDs of
different sizes (originally immersed in Toluene) with emission bands around 877 nm (PbS877), 1160 nm
(PbS1160) and 1474 nm (PbS1474) were inserted inside the silica MOF structure by using an N2 gas pressure
system. The broadband luminescence spectra varying from around 1000 nm to 1600 nm were obtained by using
QDs mixtures spread around MOF core surfaces. This QDs spread technique and the PbS QDs broadband
luminescence spectra results could have potential applications in optical amplifier,sensor and nonlinear optical
fiber loop mirror devices.
In this work, we report results of lead sulfide (PbS) quantum dots (QDs) luminescence spectra evolution during the
QDs spread process around the core of silica micro-structured (MS) fibers. These QDs are excited, via evanescent
field effect, with a 532nm or 785nm laser guided by the MS-fiber cores. The PbS-core QDs of different sizes
(originally immersed in Toluene) with emission bands around 877 nm (PbS877), 1160 nm (PbS1160) and 1474 nm
(PbS1474) were inserted inside the silica MS-fiber structure by using an N2 gas pressure system. The broadband
luminescence spectra varying from around 1000 nm to 1600 nm were obtained by using QDs mixtures impregnated
around MS-fiber core surfaces. This QDs spread technique and the PbS QDs broadband luminescence spectra results
could have potential applications in optical amplifier,sensor and nonlinear optical fiber loop mirror devices.
We report the fabrication of glass multilayer doped with semiconductor nanoparticles. The glass
matrix was fabricated by Plasma Enhanced Chemical Deposition (PECVD using tetramethoxysilane
(TMOS) as precursor. The RF power was supplied by a RF-150 TOKYO HI-Power operating at
13.56 MHz and coupled to the RF electrodes through a matching box. The nanoparticles were
grown by pulsed laser deposition (PLD) of a PbTe target using the second harmonic of a Q-Switched
Quantel Nd:YAG laser in high purity inert gas atmosphere.
The influence of gas and background pressure and in the nanoparticle size and size distribution is
studied. The morphological properties of the nanostructured material were studied by means of High
Resolution Transmission Electron Microscopy(HRTEM), grazing-incidence smallangleX-ray
scattering (GISAXS).
Semiconductor quantum dots [QD] have shown a great number of applications from fluorescent markers to solar cell
devices. Colloidal systems have been usually obtained through chemical synthesis, that have to be devoleped for each
material. The best quality QDs have been obtained with non-aqueous solution and non-physiological pH, requiring a
posterior processing to be used in biology, for example. In contrast, the same physical synthetic method, such as laser
ablation, would be applied to any semiconductor, metallic or dielectric material. Colloidal QD can be obtained by laser
ablation of a target inside any solvent, given this method a very large flexibility. The fluorescence efficiency, however,
depend on the surface traps and stability of colloids. The usual method to avoid surface traps is to grow a cap layer to
passivate its surface and, at the same time, stabilize the colloid, sterically or electrostatically.
In this work we report a novel technique for obtain thiol capped CdTe colloidal quantum dots in one step. A
target immerse in a solution of ethanol and 3-mercaptopropyltrimethoxysilane (MPS), or thiol, was hit by a nanosecond
532 nm laser. With this assembly CdTe luminescent QDs were obtained. The colloid photoluminescence and other
optical and structural properties are studied.
In this work we report a novel technique for obtain thiol capped CdTe colloidal
quantum dots in one step. These nanoparticles are compatible for silica capping indicating their
possible use as fluorescent markers.
Semiconductor colloidal quantum dots have been, for the past two decades, incorporated in a wide range of
applications from catalysis and optical sensors to biolabels. For this reason, simple, cheap and reproducible routes of
synthesis are the main goal of many research groups around the world. They seek the production of a very stable and
extremely quantum efficient nanocrystal that can afford rough changes in the external environment. Silica capping is
becoming a very common tool in the quest for a stable quantum dot, because of its strong and stable structure, this
material provides a great insulator to the nanocrystal from the outside. The nanocrystal surface is not chemically
favorable to the deposition of the bare silica shell, what demands a bifunctional molecule that provides the linkage
between the core and the shell. In this work we present a comparison between several silanization methods of thiol
capped CdSe and CdTe quantum dots, showing some simplifications of the routes and an application of the quantum dots
produced as fluorescent cell markers in acquisition of confocal microscopy images.
One of the fundamental goals in biology is to understand the interplay between biomolecules of different cells. This
happen, for example, in the first moments of the infection of a vector by a parasite that results in the adherence to the cell
walls. To observe this kind of event we used an integrated Optical Tweezers and Confocal Microscopy tool. This tool
allow us to use the Optical Tweezers to trigger the adhesion of the Trypanosoma cruzi and Trypanosoma rangeli parasite
to the intestine wall cells and salivary gland of the Rhodnius prolixus vector and to, subsequently observe the sequence
of events by confocal fluorescence microscopy under optical forces stresses. We kept the microorganism and vector cells
alive using CdSe quantum dot staining. Besides the fact that Quantum Dots are bright vital fluorescent markers, the
absence of photobleaching allow us to follow the events in time for an extended period. By zooming to the region of
interested we have been able to acquire confocal images at the 2 to 3 frames per second rate.
We present Raman-scattering results for PbTe quantum dots (QDs) in doped telluride glasses which clearly
show the confinement effects on the phonon spectra as a function of the quantum-dot size.
Laser ablation (LA) is a thin film fabrication technique which has generated a lot
of interest in the past few years as one of the simplest and most versatile methods for the
deposition of a wide variety of materials. With the rapid development experienced in the
generation of ultra short laser pulses, new possibilities were opened for the laser ablation
technique, using femtosecond lasers as ablation source. It is commonly believed that
when the temporal length of the laser pulse became shorter than the several picoseconds
required to couple the electronic energy to the lattice of the material, thermal effects
could not play a significant role. Since the pulse width is too short for thermal effects to
take place, with each laser pulse a few atom layers of material are direct vaporized away
from the target surface and a better control in the quantum dots (QDs) fabrication could
be achieved.
In this work we report the fabrication of PbTe QDs by femtosecond laser ablation of a
PbTe target in argon atmosphere. Experiments were carried out using a typical LA
configuration comprising a deposition chamber and an ultra short pulsed laser (100 fs; 30
mJ) at a central wavelength of 800 nm. PbTe was chosen because its QDs absorption
band can be controlled by its size to fall in the spectral window of interest for optical
communications (1.3-1.5 μm). This, together with the QD high optical nonlinearity,
makes this material an excellent candidate for development of photonic devices.
It was investigated the influence of the number of laser pulses in the formation of the
nanoparticles. The structural parameters and the surface density of the nanoparticles were
studied by high resolution transmission electron microscopy (HRTEM).
PbTe doped tellurite glass photonic optical fiber for non linear application were developed using rod in tube method in a
draw tower. We follow the growth kinetics of the quantum dots in the optical fiber by High Resolution Transmission
Electron Microscopy giving some results related with the growth kinetic of the same in function of time so much for
optical fiber as for the glass bulk. Absorption peak near 1500 nm as observed and it was attributed the optical resonance
due PbTe quantum dots in the core fiber.
In the past it was observed that buck ball doped glasses showed enhanced optical
nonlinearities. However, carbon nanotubes are much more stable than buck ball and
should be a better choice for that purpose. Therefore we decided to investigate the
possibility to produce carbon nanotubes doped tellurite glasses and measured their
optical nonlinearities. Tellurite glasses already have a larger nonlinearity compared to
silica, and other, glasses. We produced TeO2-ZnO tellurite family glasses doped with
multi wall Carbon Nanotube (CNT). The CNTs acquired from Carbolex were
vigorously mechanically mixed with the tellurite glass precursors and melted in
platinum crucible around 650°C in a controlled atmosphere inside an electrical induction
furnace. We used the lowest temperature possible and controlled atmosphere to avoid
the CNT oxidation. The glass melt was cast in a stainless steel and thermally treated at
300°C for 5 hours to relieve internal stresses. The samples were than cutted and
polished to perform the optical characterization. We measured refractive index and
thermo physical properties, such as vitreous transition Tg, crystallization onset Tx and
melting Tf temperatures. Raman spectroscopy showed the possible presence of CNTs.
Red blood cell (RBC) aggregation in the blood stream is prevented by the zeta potential created by its negatively charged membrane. There are techniques, however, to decrease the zeta potential and allow cell agglutination, which are the basis of most of antigen-antibody tests used in immunohematology. We propose the use of optical tweezers to measure membrane viscosity, adhesion, zeta potential, and the double layer thickness of charges (DLT) formed around the cell in an electrolytic solution. For the membrane viscosity experiment, we trap a bead attached to RBCs and measure the force to slide one RBC over the other as a function of the velocity. Adhesion is quantified by displacing two RBCs apart until disagglutination. The DLT is measured using the force on the bead attached to a single RBC in response to an applied voltage. The zeta potential is obtained by measuring the terminal velocity after releasing the RBC from the trap at the last applied voltage. We believe that the methodology proposed here can provide information about agglutination, help to improve the tests usually performed in transfusion services, and be applied for zeta potential measurements in other samples.
In this work we report the fabrication of PbTe quantum dots multilayers embedded in SiO2 by
alternatively use of Laser Ablation and Plasma Enhanced Chemical Vapor Deposition
techniques. The quantum dots were grown by pulsed laser deposition (PLD) of a PbTe target
using the second harmonic of a Q-Switched Quantel Nd:YAG laser in high purity argon
atmosphere. The glass matrix was fabricated by PECVD using tetramethoxysilane (TMOS) as
precursor. The RF power was supplied by a RF-150 TOKYO HI-Power operating at 13.56 MHz
and coupled to the RF electrodes through a matching box. The deposition rates as well as the best
growth parameters for both the nanoparticles and the glass matrix were obtained from a previous
work. The morphological properties of the nanostructured material were studied by means of igh
Resolution Transmission Electron Microscopy(HRTEM), grazing-incidence small-angle X-ray
scattering (GISAXS) and X-ray reflectometry . Unlike HRTEM, which extracts information of a
submicron region of the sample and only a few thousand particles are observed, GISAXS signal
is obtained through an average over orders of magnitude larger number of particles (perhaps 1012
particles) distributed over an area of tens of square millimeters. This fact means that GISAXS
sampling is much more representative of the sample as whole.
Finally, multilayers were grown inside a Fabry-Perot cavity. The complete system operates as
an optical switching device for the infrared region. The device was characterized by Scanning
Electron Microscopy and optical absorption.
PbTe thin films were grown on BK7 glass and Si(100) substrates using femtosecond pulsed laser deposition at room temperature. The influence of the background pressure and the laser fluence on the structural and optical characteristics of the PbTe films was
studied. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to characterize the surface and structural properties of the deposited PbTe thin films, respectively. Transmission spectroscopy measurements in the visible and infrared region
(VIS-IR) were used to investigate the optical properties of the PbTe thin films.
The research in biomedical photonics is clearly evolving in the direction of the understanding of biological
processes at the cell level. The spatial resolution to accomplish this task practically requires photonics tools.
However, an integration of different photonic tools and a multimodal and functional approach will be necessary to
access the mechanical and biochemical cell processes. This way we can observe mechanicaly triggered biochemical
events or biochemicaly triggered mechanical events, or even observe simultaneously mechanical and biochemical
events triggered by other means, e.g. electricaly. One great advantage of the photonic tools is its easiness for
integration. Therefore, we developed such integrated tool by incorporating single and double Optical Tweezers with
Confocal Single and Multiphoton Microscopies. This system can perform 2-photon excited fluorescence and Second
Harmonic Generation microscopies together with optical manipulations. It also can acquire Fluorescence and SHG
spectra of specific spots. Force, elasticity and viscosity measurements of stretched membranes can be followed by
real time confocal microscopies. Also opticaly trapped living protozoas, such as leishmania amazonensis.
Integration with CARS microscopy is under way. We will show several examples of the use of such integrated
instrument and its potential to observe mechanical and biochemical processes at cell level.
The red blood cell (RBC) viscoelastic membrane contains proteins and glycoproteins embedded in a fluid lipid bilayer that are responsible for cell agglutination. Manipulating RBCs rouleaux with a double optical tweezers, we observed that the cells slide easily one over the others but are strongly connected by their edges. An explanation for this behavior could be the fact that when the cells slide one over the others, proteins are dragged through the membrane. It confers to the movement a viscous characteristic that is dependent of the velocity between the RBCs and justifies why is so easy to slide them apart. Therefore, in a first step of this work, by measuring the force as a function of the relative velocity between two cells, we confirmed this assumption and used this viscous characteristic of the RBC rouleaux to determine the apparent membrane viscosity of the cell. As this behavior is related to the proteins interactions, we can use the apparent membrane viscosity to obtain a better understanding about cell agglutination. Methods related to cell agglutination induced by antigen-antibody interactions are the basis of most of tests used in transfusion centers. Then, in a second step of this work, we measured the apparent membrane viscosity using antibodies. We observed that this methodology is sensitive to different kinds of bindings between RBCs. Better comprehension of the forces and bindings between RBCs could improve the sensibility and specificity of the hemagglutination reactions and also guides the development of new potentiator substances.
The red blood cell (RBC) viscoelastic membrane contains proteins and glycolproteins embedded in, or attached, to a
fluid lipid bilayer and are negatively charged, which creates a repulsive electric (zeta) potential between the cells
and prevents their aggregation in the blood stream. The basis of the immunohematologic tests is the interaction
between antigens and antibodies that causes hemagglutination. The identification of antibodies and antigens is of
fundamental importance for the transfusional routine. This agglutination is induced by decreasing the zeta-potential
through the introduction of artificial potential substances. This report proposes the use of the optical tweezers to
measure the membrane viscosity, the cell adhesion, the zeta-potential and the size of the double layer of charges
(CLC) formed around the cell in an electrolytic solution. The adhesion was quantified by slowly displacing two
RBCs apart until the disagglutination. The CLC was measured using the force on the bead attached to a single RBC
in response to an applied voltage. The zeta-potential was obtained by measuring the terminal velocity after releasing
the RBC from the optical trap at the last applied voltage. For the membrane viscosity experiment, we trapped a bead
attached to RBCs and measured the force to slide one RBC over the other as a function of the relative velocity. After
we tested the methodology, we performed measurements using antibody and potential substances. We observed that
this experiment can provide information about cell agglutination that helps to improve the tests usually performed in
blood banks. We also believe that this methodology can be applied for measurements of zeta-potentials in other kind of samples.
A new polymeric open optical fiber with a star cross section from extruded PMMA grains was
developed. We have painted the external surface of this fiber with the Europium chelate or
Antracene. We have observed the typical luminescence of these compounds when excited with
nanosecond 355 nm pulsed laser. These results show that the developed fiber presents potentialities
for optical sensing.
We have been able to produce soft glass conventional core-clad and micro-structured fibers using rod-and-tube and stack-and-draw method respectively. The stack-and-draw technique shows several difficulties when used with soft glasses, that we managed to avoid using two different lead and alkaline glasses. Non commercial glasses and fibers were thermo-mechanically and optically characterized.
Tellurite glasses are important as a host of Er3+ ions because of their great solubility and because they present broader
gain bandwidths than Er3+-doped silica, with promise to increase the bandwidth of communication systems. However,
the small glass stability range (GSR) of tellurite glasses compromises the quality of the optical fibers. We show that the
addition of CsCl to tellurite glasses can increase their GSR, making it easier to draw good quality optical fibers. CsCl
acts as a network modifier in glass systems, weakening the network by forming Te-Cl bonds. We show that the thermal
expansion coefficient mismatch is in the right direction for optical fiber fabrication purposes and that the Bi2O3 content can be used to control the refractive index of clad and core glasses. Single-mode and multi-mode Er3+-doped optical
fibers were produced by the rod-in-tube method using highly homogeneous TeO2-ZnO-Li2O-Bi2O3-CsCl glasses. Far infrared spectra of the glass samples exhibit absorption bands of the Te-Cl bond.
Chemotaxis is the mechanism microorganisms use to sense the environment surrounding them and to direct their
movement towards attractive, or away from the repellent, chemicals. The biochemical sensing is almost the only way for
communication between unicellular organisms. Prokaryote and Eukaryote chemotaxis has been mechanically studied
mainly by observing the directionality and timing of the microorganisms movements subjected to a chemical gradient,
but not through the directionality and strength of the forces it generates. To observe the vector force of microorganisms
under a chemical gradient we developed a system composed of two large chambers connected by a tiny duct capable to
keep the chemical gradient constant for more than ten hours. We also used the displacements of a microsphere trapped in
an Optical Tweezers as the force transducer to measure the direction and the strength of the propulsion forces of
flagellum of the microorganism under several gradient conditions. A 9μm diameter microsphere particle was trapped
with a Nd:YAG laser and its movement was measured through the light scattered focused on a quadrant detector. We
observed the behavior of the protozoa Leishmania amazonensis (eukaryote) under several glucose gradients. This
protozoa senses the gradient around it by swimming in circles for three to five times following by tumbling, and not by
the typical straight swimming/tumbling of bacteria. Our results also suggest that force direction and strength are also
used to control its movement, not only the timing of swimming/tumbling, because we observed a higher force strength
clearly directed towards the glucose gradient.
One very important contribution of the Optical Tweezers technique is its ability to extract the missing mechanical
measurements in the world of microorganisms and cells that could be correlated to biochemical information. A
microsphere displacement is the preferential force transducer for this kind of measurement. However, the typical
conditions used in Optical Tweezers with very high numerical aperture beams and microspheres with diameters up to ten
wavelengths, requires a full vectorial description of the incident beam in partial waves with the origin of coordinate
system at the center of the microsphere and not at the focus of the beam. Using the Angular Spectrum Representation of
the incident beam and an analytical expression for integrals involving associated Legendre Polynomials, Bessel
functions and plane waves we have been able to obtain a closed expression, without any approximation, for the beam
shape coefficients of any orthogonally incident beam. The theoretical prediction of the theory agrees well with the
experimental results performed on a 3D positioned dual trap in an upright standard optical microscope, thus obtaining
the whole optical force curves as a function of the microsphere center for different wavelengths.
Multilayers of PbTe quantum dots embedded in SiO2 were fabricated by alternatively use of Laser
Ablation and Plasma Enhanced Chemical Vapor Deposition techniques. A set o samples containing
different PbTe nanoparticles sizes was prepared for the study. The morphological properties of the
nanostructured material were studied by means of grazing-incidence small-angle X-ray scattering
(GISAXS) and x-ray reflectometry (XRR) techniques. A preliminary analysis of the GISAXS
spectra provided information about the multilayer periodicity and its relationship to the size of the
deposited PbTe nanoparticles.
Multilayers of PbTe quantum dots embedded in SiO2 were fabricated and characterized by
means of Fourirer transform infrared and x-ray spectrometry and transmission electron
microscopy. The quantum dots were grown by laser ablation of a PbTe target using the second
harmonic of a Q-Switched Quantel Nd:YAG laser under high purity argon atmosphere. The
glass matrix was fabricated by Plasma Enhanced Chemical Vapor Deposition using
tetramethoxysilane as precursor. The reason for choosing PbTe was the absorption bands this
material exhibits in the region of interest for optical communications 1.3-1.5μm making this
material an excellent candidate for development of optical devices.
For the glass matrix, it was studied the influence of growing parameters like RF power,
distance between the RF electrodes and the total pressure in the properties of the SiO2 films. The
parameters for the PbTe ablation were assumed from a previous work. FTIR and refractive index
measurements were used to estimate the best growth parameters for the dielectric host.
TMOS partial pressure proved to be an important parameter to diminish the nanoparticle
coalescence during the multilayer fabrication. Multilayer X-ray diffraction patterns were used to
estimate the nanoparticles diameter. Morphological properties of the nanostructured material
were studied using transmission electron microscopy.
The displacements of a dielectric microspheres trapped by an optical tweezers (OT) can be used as a force transducer for mechanical measurements in life sciences. This system can measure forces on the 50 femto Newtons to 200 pico Newtons range, of the same order of magnitude of a typical forces induced by flagellar motion. The process in which living microorganisms search for food and run away from poison chemicals is known is chemotaxy. Optical tweezers can be used to obtain a better understanding of chemotaxy by observing the force response of the microorganism when placed in a gradient of attractors and or repelling chemicals. This report shows such observations for the protozoa Leishmania amazomenzis, responsible for the leishmaniasis, a serious tropical disease. We used a quadrant detector to monitor the movement of the protozoa for different chemicals gradient. This way we have been able to observe both the force strength and its directionality. The characterization of the chemotaxis of these parasites can help to understand the infection mechanics and improve the diagnosis and the treatments employed for this disease.
We present degenerate and nondegenerate two-photon absorption spectra in a series of CdSe and CdTe quantum dots. The measurements show that the two-photon absorption (2PA) spectrum is strongly dependent on the quantum dot size and that the 2PA coefficient decreases as the quantum dot size decreases, and it is larger for the frequency nondegenerate process. Previously we had shown a theoretical analysis of these results based on a simple model using the effective mass approximation. Although this model works well for larger quantum dots, it fails for the smaller ones. Here we use the more (formula available in manuscript) model for the band structure and consider the hole band mixing in quantum dots to describe our data. This theory better describes the spectral structures for smaller quantum dots and also predicts the decrease of the 2PA coefficient with the decrease of quantum dot size. This is due to the reduction of the number of possible transitions and the blue shift of the optical bandgap from quantum confinement. This theory predicts the reduction of the 2PA coefficient with size, although our experimental results show an even stronger reduction.
The fluid lipid bilayer viscoelastic membrane of red blood cells (RBC) contains antigen glycolproteins and proteins which can interact with antibodies to cause cell agglutination. This is the basis of most of the immunohematologic tests in blood banks and the identification of the antibodies against the erythrocyte antigens is of fundamental importance for transfusional routines. The negative charges of the RBCs creates a repulsive electric (zeta) potential between the cells and prevents their aggregation in the blood stream. The first counterions cloud strongly binded moving together with the RBC is called the compact layer. This report proposes the use of a double optical tweezers for a new procedure for measuring: (1) the apparent membrane viscosity, (2) the cell adhesion, (3) the zeta potential and (4) the compact layer's size of the charges formed around the cell in the electrolytic solution. To measure the membrane viscosity we trapped silica beads strongly attached to agglutinated RBCs and measured the force to slide one RBC over the other as a function of the relative velocity. The RBC adhesion was measured by slowly displacing two RBCs apart until the disagglutination happens. The compact layer's size was measured using the force on the silica bead attached to a single RBC in response to an applied voltage and the zeta potential was obtained by measuring the terminal velocity after releasing the RBC from the optical trap at the last applied voltage. We believe that the methodology here proposed can improve the methods of diagnosis in blood banks.
Partial wave decomposition of incident beams is the first task to be performed to impose boundary conditions at the particle interface in the calculation of the scattering of spherical particles. The coordinate's origin must be in the center of the particle and not at high symmetry positions of the beam. This can be a quite complicated problem, especially when a full vectorial diffraction description of the electromagnetic fields and highly focused laser beams are required where the paraxial limit fails. Traditional approximation techniques have been used to proceed forward and to obtain numerical results. The main fault relies on a radial dependence of the beam shape coefficients, which limits the validity of such approximations. Here we prove that the radial dependence will emerge from the solid angle integration in this way obtaining an exact, closed expression, without any approximation, for the beam shape coefficients, for an arbitrary beam shape, origin and polarization, the special case of a Gaussian beam is presented.
The ability to observe quantitatively mechanical events in real time of biological phenomena is an important contribution
of the Optical Tweezers technique for life sciences. The measurements of any mechanical property involves force
measurements, usually performed using a microsphere as the force transducer. This makes the understanding of the
photonic force theory critical. Only very sensitive and precise experimental 3D photonic force measurements for any
particle size will be able to discriminate between different theoretical models. In particular it is important to obtain the
whole photonic force curve as a function of the beam position instead of isolate particular points. We used a dual trap in
an upright standard optical microscope, one to keep the particle at the equilibrium position and the other to disturb it.
With this system we have been able to obtain these force curves as a function of x, y and z position, incident beam
polarization and wavelength. We investigated the optical forces for wavelengths in and out of Mie resonances of
dielectric microspherical cavities for both TM and TE modes and compared the experimental results with the
calculations performed with different models for the optical force.
Micro-structured Er3+ - Tm3+ co-doped tellurite fiber with three rings of holes was
fabricated using a soft glass drawing tower by a stack-and-draw technique. Amplified
spontaneous emission (ASE) around 1550nm band were observed when pumped with both,
980nm and 790nm, lasers.
In this work we used a Thermal Mechanic Analysis equipment to produce the channel FOG waveguides by pressing an Er3+ doped tellurite glass optical fiber against one Er3+ ion doped tellurite glass substrate kept under Tc ± 30 oC (Tc = soft point). The luminescence and waveguide refractive index were measured. Scanning electron microscopy was used to observe the obtained structure. The objective is to produce a new concept in components of integrated optical circuits. Then this work report the production of Er3+-doped tellurite glass channel waveguides using the novel concept of Benson et al[1] of fiber on glass (FOG). To succeed with this technique it is important to correlate the main thermo-physical characteristics of the substrate and the fiber, which are the transition temperature Tg, the temperature of the onset of crystallization Tx, the maximum crystallization temperature Tc and the thermal expansion coefficient. The Tg, Tx and Tc values were determined by Differential Thermal Analysis (DTA), while the thermal expansion coefficient was determined by Thermal Mechanical Analysis (TMA). For the FOG purpose the thermal stability range, Tx - Tg, is an important temperature region which defines if the glass will have enough viscosity to shape in the FOG concept.
This work reports the fabrication of planar and channel waveguides by Ag+ → Na+ ion exchange in an Er3+ doped tellurite glass with a composition of 75TeO2-2GeO2-10Na2O-12ZnO-1Er2O3 (mol %). The glass was chemically stable during the ion-exchange process. We have been able to produce single and multi-mode planar waveguides controlling the depths of the waveguides by varying ion-exchange temperatures, from 250 to 280 °C, and times, from 3 to 12 h. We also show preliminary results of channel waveguide fabrication with the same technique. The waveguide effective refractive index curves and attenuation (11 dB/cm) at 1536 nm were measured with a Metricom prism coupler. The Amplified Spontaneous Emission (ASE) spectra showed a 152 nm bandwidth when pumped with 120 mW laser pump at 980 nm.
Thermal Lens (TL) and spectroscopic characterizations were performed in 70TeO2-19WO3-7Na2O-4Nb2O5 (mol%) tellurite glasses. TL measurements were accomplished in Er3+ /Tm3+ co-doped tellurite glasses in function of the Tm2O3 concentration (0.4-1.6 x1020 ions/cm3). Fluorescence spectra at 488 nm showed that Er3+ /Tm3+ co-doped tellurite glasses present several emission bands between (500-1800) nm. However, the more intense emission bands correspond to the Tm3+ and Tm3+ transitions (4I13/2 → 4I15/2 and 3F4 → 3H6), respectively. The absolute nonradiative quantum efficiency (φ) was determined by TL method. Higher values of φ were obtained with the increase of Tm2O3 concentration inside of the Er3+/Tm3+ co-doped tellurite glasses. These results are corroborated by the Judd-Ofelt calculations.
Er3+-Tm3+ co-doped tellurite photonic crystal fiber was fabricated via a stack-and-draw procedure and without using extrusion in any stage. The final fiber presents a 187 nm bandwidth of amplified spontaneous emission (ASE) intensity around 1550nm when pumped with 790nm. In this manuscript a soft-glass tube fabrication technique, using the centrifugation method, is also shown.
The red blood cell (RBC) viscoelastic membrane contains proteins and glycolproteins embedded in, or attached, to a fluid lipid bilayer and are negatively charged, which creates a repulsive electric (zeta) potential between the cells and prevents their aggregation in the blood stream. There are techniques, however, to decrease the zeta potential to allow cell agglutination which are the basis of most of the tests of antigen-antibody interactions in blood banks. This report shows the use of a double optical tweezers to measure RBC membrane viscosity, agglutination and zeta potential. In our technique one of the optical tweezers trap a silica bead that binds strongly to a RBC at the end of a RBCs rouleaux and, at the same time, acts as a pico-Newton force transducer, after calibration through its displacement from the equilibrium position. The other optical tweezers trap the RBC at the other end. To measure the membrane viscosity the optical force is measured as a function of the velocity between the RBCs. To measure the adhesion the tweezers are slowly displaced apart until the RBCs disagglutination happens. The RBC zeta potential is measured in two complimentary ways, by the force on the silica bead attached to a single RBC in response to an applied electric field, and the conventional way, by the measurement of terminal velocity of the RBC after released from the optical trap. These two measurements provide information about the RBC charges and, also, electrolytic solution properties. We believe this can improve the methods of diagnosis in blood banks.
Fluorescent semiconductor nanocrystals in quantum confinement regime (quantum dots) present several well known features which make them very useful tools for biological labeling purposes. Low photo-bleaching rates, high chemical stability, active surface allowing conjugation to living cells, explains the success of this labeling procedure over the commonly used fluorescent dyes. In this paper we report the results obtained with high fluorescent core-shell CdTe-CdS (diameter = 3-7 nm) colloidal nanocrystals synthesized in aqueous medium and conjugated to glucose molecules, incubated with living yeast cells, in order to investigate their glucose up-take activity.
Since optical tweezers trapped microspheres can be used as an ultrasensitive force measurements technique, the knowledge of its theoretical description is of utmost importance. However, even the description of the incident electromagnetic fields under very tight focusing, typical of the optical trap, is not yet a closed problem. Therefore it is important to experimentally obtain whole accurate curves of the force as a function of wavelength, polarization and incident beam 3D position with respect to the center of the microsphere. Theoretical models for optical forces such as the Generalized Lorenz-Mie theory, can then be applied to the precisely evaluated experimental results. Using a dual trap in an upright standard optical microscope, one to keep the particle at the equilibrium position and the other to disturb it we have been able to obtain these force curves as a function of x, y and z position, incident beam polarization and also wavelength. Further investigation of optical forces was conducted for wavelengths in and out Mie resonances of the dielectric microspherical cavities for both TM and TE modes.
Multilayer of PbTe quantum dots embedded in SiO2 were fabricated by alternatively use of Plasma Enhanced Chemical Vapor Deposition and Laser Ablation techniques. The optimal growing parameters for both the SiO2 films and the PbTe quantum dots were obtained. The refractive index and optical absorption of the sample were studied. Multilayer X-ray diffraction patterns were used to estimate the nanoparticles diameter. Morphological properties of the nanostructured material were studied using Transmission Electron Microscopy. Both absorption spectra and X-ray diffraction patterns reveled the nanoparticles are 6-8 nm in diameter, consequently appropriate for developing optical devices in the infra red region. Finally the multilayer was grown inside a Fabry Perot cavity. The transmittance of the one-dimensional photonic crystal was measured.
The displacements of a polystyrene microsphere trapped by an optical tweezers (OT) can be used as a force transducer for mechanical measurements in life sciences such as the measurement of forces of living microorganisms or the viscosity of local fluids. The technique we used allowed us to measure forces on the 200 femto Newtons to 4 pico Newtons range of the protozoa Leishmania amazonensis, responsible for a serious tropical disease. These observations can be used to understand the infection mechanism and chemotaxis of these parasites. The same technique was used to measure viscosities of few microliters sample with agreement with known samples better than 5%. To calibrate the force as a function of the microsphere displacement we first dragged the microsphere in a fluid at known velocity for a broad range of different optical and hydrodynamical parameters. The hydrodynamical model took into account the presence of two walls and the force depends on drag velocity, fluid viscosity and walls proximities, while the optical model in the geometric optics regime depends on the particle and fluid refractive indexes and laser power. To measure the high numerical (NA) aperture laser beam power after the objective we used an integration sphere to avoid the systematic errors of usual power meters for high NA beams. After this careful laser power measurement we obtained an almost 45 degrees straight line for the plot of the optical force (calculated by the particle horizontal displacement) versus hydrodynamic force (calculated by the drag velocity) under variation of all the parameters described below. This means that hydrodynamic models can be used to calibrate optical forces, as we have done for the parasite force measurement, or vice-versa, as we did for the viscosity measurements.
In this work we developed a setup consisting of an Optical Tweezers equipped with linear and non-linear micro-spectroscopy system to add the capabilities of manipulation and analysing captured objects. Our setup includes a homemade confocal spectrometer using a monochromator equipped with a liquid nitrogen cooled CCD. The spectroscopic laser system included a cw and a femtosecond Ti:sapphire lasers that allowed us to perform Raman, hyper-Raman, hyper-Rayleigh and two photon Excited (TPE) luminescence in particles trapped with an Nd:YAG cw laser. We obtained Raman spectra of a single trapped polystyrene microsphere and a single trapped red blood cell to evaluate the performance of our system. We also observed hyper-Rayleigh and hyper-Raman peaks for SrTiO3 with 60s integration time only. This was possible because the repetition rate of the femtosecond Ti:sapphire lasers, on the order of 80 MHz, are much higher than the few kHz typical picosecond laser repetition rate used before in hyper- Raman experiment, which required acquisition times of order of few hours. We used this system to perform scanning microscopy and to acquire TPE luminescence spectra of captured single stained microsphere and cells conjugated with quantum dots of CdS and CdTe and hyper-Rayleigh spectra of a noncaptured ZnSe microparticle. The results obtained show the potential presented by this system and fluorescent labels to perform spectroscopy in a living trapped microorganism in any neighbourhood and dynamically observe the chemical reactions changes in real time.
Both degenerate and nondegenerate two-photon absorption (2PA) spectra are studied in two different samples of CdTe quantum-dots in borosilicate glass hosts. One sample (CdTe-600) contains quantum-dots of radius 3.2 ± 0.2 nm and has its absorption edge at 600nm. The other sample (CdTe-750) contains quantum-dots of radius 6.6 ± 0.9 nm and absorption edge at 750nm. CdTe-600 contains quantum-dots with a narrower size distribution than CdTe-750. Consequently, the peaks corresponding to discrete transitions are more clearly visible in CdTe-600 than in CdTe-750. Both nondegenerate and degenerate spectra for these samples show a marked difference from bulk CdTe. In CdTe-750 the two-photon absorption spectrum has a shape similar to that for bulk solids but for CdTe-600 the 2PA spectrum is somewhat different from that expected for the bulk. In the Z-scan measurements we also observed a photo-darkening effect, which is accompanied by an increase in the measured effective 2PA coefficient. All results suggest that 2PA cannot be predicted by the bulk theory especially near to the 2PA edge, that the 2PA in quantum dots is generally smaller than would be expected for the same volume of bulk semiconductor with the same band edge, and that the quantum-dot size and size distribution play important roles in the 2PA spectral behavior and magnitude.
Up to now optical spectroscopies have analyzed the scattered light or the heat generated by absorption as a function of the wavelength to get information about the samples. Among the light matter interaction phenomena one that has almost never been used for spectroscopy is the direct photon momenta transfer. Probably because the forces involved are very small, varying from hundreds of femto to tens of pico Newtons. However, the nowadays very popular Optical Tweezers can easily accomplish the task to measure the photon momenta transfer and may be the basis for the Optical Force Spectroscopy. We demonstrate its potential as such a tool by observing more than eight Mie resonance peaks of a single polystyrene microsphere, and showed the capability to selective couple the light to either the TE, TM or both microsphere modes depending of the beam size, the light polarization and the beam positioning. The Mie resonances can change the optical force values by 30-50%. Our results also clearly show how the beam polarization breaks the usually assumed azimuthal symmetry by Optical Tweezers theories. We also obtained the spectrum from the two photon excited luminescence using the Optical Tweezers to hold a single bead suspended and a femtosecond Ti:sapphire laser for the non-linear excitation. This spectrum shows the pair of peaks due to both TE and TM spherical cavity modes. We have been able to observe more than 14 Mie resonance peaks in the TPE luminescence. Our results are in good agreement with optical force calculations using Maxwell stress tensor and partial wave decomposition of the incident beam approximated to a 3th order gaussian beam.
We have developed a method for measuring the red blood cell (RBC) membrane overall elasticity μ by measuring the deformation of the cells when dragged at a constant velocity through a plasma fluid by an optical tweezers. The deformability of erythrocytes is a critical determinant of blood flow in the microcirculation. We tested our method and hydrodynamic models, which included the presence of two walls, by measuring the RBC deformation as a function of drag velocity and of the distance to the walls. The capability and sensitivity of this method can be evaluated by its application to a variety of studies, such as, the measurement of RBC elasticity of sickle cell anemia patients comparing homozygous (HbSS), including patients taking hydroxyrea (HU) and heterozygous (HbAS) with normal donors and the RBC elasticity measurement of gamma irradiated stored blood for transfusion to immunosupressed patients as a function of time and dose. These studies show that the technique has the sensitivity to discriminate heterozygous and homozygous sickle cell anemia patients from normal donors and even follow the course of HU treatment of Homozygous patients. The gamma irradiation studies show that there is no significant change in RBC elasticity over time for up to 14 days of storage, regardless of whether the unit was irradiated or not, but there was a huge change in the measured elasticity for the RBC units stored for more than 21 days after irradiation. These finds are important for the assessment of stored irradiated RBC viability for transfusion purposes because the present protocol consider 28 storage days after irradiation as the limit for the RBC usage.
In this work we present the fabrication of tellurite glass photonic crystal fiber doped with a very large erbium concentration. Tellurite glasses are important hosts for rare earth ions due to its very high solubility, which allows up to 10,000 ppm Er3+ concentrations. The photonic crystal optical fibers and tellurite glasses can be, therefore, combined in an efficient way to produce doped fibers for large bandwidth optical amplifiers. The preform was made of a 10 mm external diameter tellurite tube filled with an array of non-periodic tellurite capillaries and an erbium-doped telluride rod that constitute the fiber core. The preform was drawn in a Heathway Drawing Tower, producing fibers with diameters between 120 - 140 μm. We show optical microscope photography of the fiber’s transverse section. The ASE spectra obtained with a spectra analyzer show a red shift as the length of the optical fiber increases.
Thin films of glass doped with PbTe quantum dots were successfully fabricated. The semiconducting quantum dots were grown by laser ablation of a PbTe target (99.99%) using the second harmonic of a Q-Switched Quantel Nd:YAG laser under high purity argon atmosphere. The glass matrix was fabricated by a plasma chemical vapor deposition method using vapor of tetramethoxysilane (TMOS) as precursor. The QD's and the glass matrix were alternately deposited onto a Si (100) wafer for 60 cycles. Cross-section TEM image clearly showed QD's layer well separated from each other with glass matrix layers. The influence of the ablation time on the size distribution of the quantum dots is studied. HRTEM revealed anisotropy in the size of the QD's: they were about 9nm in the high and 3-5 in diameter. Furthermore HRTEM studies revealed that the QD's basically growth in the (200) and (220) directions. The thickness of the glass matrix layer was about 20 nm. Absorption, photo luminescence and relaxation time of the multilayer were also measured.
Tellurite glasses optical fibers became promising for optical amplifiers due to its high rare earth ions solubility. One of the most important parameter for optical amplification is the lifetime of the excited states, which strongly depends on the crystal field around the ions. That crystal field changes dramatically with the host glass and with rare earth concentration. Excited state lifetime studies have been performed on Er3+-doped-TeO2-WO3-Na2O-Nb2O5 glass system. Therefore, we decided to study the Er3+ excited states lifetimes and compared with the Judd-Ofelt theory predictions. We measured only the 4I13/2 to 4I15/2 transitions lifetimes. The other transitions lifetimes can be inferred by knowing the Ω2, Ω4, Ω6 Judd-Ofelt parameters. These parameters were calculated with the electric-magnetic dipole transition oscillator strength for the desired excited levels and ground state obtained from the optical absorption spectra. After performing this calculation we estimated that maximum quantum efficiency (η), measured/calculated lifetimes ratio, would be achieved at 7500ppm (%wt) Er3+ content.
Semiconductor nanocrystals composed by few hundred to a few thousand atoms also known as quantum dots have received substantial attention due to their size tunable narrow-emission spectra and several other advantages over organic molecules as fluorescent labels for biological applications, including resistence to photodegradation, improved brightness and only one laser excitation that enable the monitoring of several processes simultaneously. In this work we have synthesized and characterized thiol-capped CdTe and bioconjugated them to macrophages. We have mapped the fluoroscence intensity along the macrophage's body in our set up consisting of an optical tweezer plus a non-linear micro-spectroscopy system to perform scanning microscopy and observe spectra using two photon excited luminescence.
Tellurite glasses optical fibers became promising for optical amplifiers due to its high rare earth ions solubility and very large amplification bandwidth. Among several tellurite glasses the TeO2-WO3-Na2O-Nb2O5 system show one of the largest bandwidth. Our previous characterization of lifetime using the omega2, omega4, omega6, Judd-Ofelt parameters indicate a quantum efficiency maximum for 7500ppm Er3+ concentration. Therefore we decided to produce jointed Er3+ and Tm3+ single mode optical fibers with this glass system keeping the 7500ppm Er3+ concentration and varying the Tm3+ concentration from 2500ppm to 15000ppm. This single mode fiber was pumped by 120mW of the semiconductor laser at 790nm and we observed a flat ASE bandwidth from 1400 to 1570nm for the 5000ppm Tm3+ concentration.
We produced a PbTe quantum dot core doped optical fiber with tellurite glasses intended to be used in highly nonlinear ultrafast optical devices capable to operate at the optical communication window at 1300 and 1500 nm wavelength region. Attenuation peaks of the optical fiber depends on the heat treatment time as expected for dots growth and covered the whole mid infrared region near 1500 nm. The optical fiber preform was made with the rod-in-tube method and the fiber was produced with a 4 m high Heatway drawing tower. The optical fiber core can be heavily doped because tellurite glasses solubility for PbTe quantum dots is order of magnitude higher than borosilicate and phosphate glasses, for example. In order to match all the requirements for core-clad optical fibers we studied undoped and doped tellurite glasses optical and thermophysical properties as a function of the glass composition. We also followed the growth kinetics of the quantum dots by High Resolution Transmission Electron Microscopy in the bulk glass matrix and the optical fiber.
In this work we used our set up consisting of an optical tweezers plus non-linear micro-spectroscopy system to perform scanning microscopy and observe spectra using two photon excited (TPE) luminescence of captured single cells conjugated with quantum dots of CdS and CdTe. The CdS nanocrystals are obtained by our group via colloidal synthesis in aqueous medium with final pH = 7 using sodium polyphosphate as the stabilizing agent. In a second step the surface of CdS particles is functionalized with linking agents such as Glutaraldehyde. The CdTe quantum dots are functionalized in the its proper synthesis using mercaptoacetic acid (AMA). We used a femtosecond Ti:sapphire laser to excite the hyper Rayleigh or TPE luminescence in particles trapped with an Nd:YAG cw laser and a 30 cm monochromator equipped with a cooled back illuminated CCD to select the spectral region for imaging. With this system we obtained hyper Rayleigh and TPE luminescence images of macrophages and other samples. The results obtained show the potential presented by this system and fluorescent labels to perform spectroscopy in a living trapped microorganism in any neighbourhood and dynamically observe the chemical reactions changes in real time.
We developed a set up consisting of an Optical Tweezers plus linear and non-linear micro-spectroscopy system to add the capabilities of manipulation and analysing the captured object. For the confocal micro-spectrometer we used a 30 cm monochromator equipped with a cooled back illuminated CCD. The spectroscopic laser system included a cw and a femtosecond Ti:sapphire lasers that allowed us to perfom raman, hyper-raman, hyper-rayleigh and two-photon excited (TPE) luminescence in trapped particles with an Nd:YAG cw laser. With the cw Ti:sapphire laser we obtained raman spectra of a single trapped polystyrene microsphere and red blood cells and silicon to evaluate the performance of our system. The femtosecond Ti:sapphire laser was used to observed hyper-rayleigh and hyper-raman peaks of SrTiO3 with 60s integration time only. In the past, hyper-raman measurements required integration times of few hours, but the huge intensity together with the 80 MHz repetition rate of the femtosecond laser decreased this time for the seconds range. The sensitiveness of our system also permitted to observe more than 14 Mie resonance peaks in the TPE luminescence of a single stained trapped microsphere, which agrees well with the calculations. This system opens up the possibility to perform spectroscopy in a living trapped micro-organism in any desired neighbourhood and dynamically observe the chemical reactions and/or mechanical properties change in real time.
Optical tweezers (OT) rely on the radiation pressure to trap and manipulate microscopic particles and living microorganisms. Because the optical forces vary from hundreds of femto to tens of pico Newtons, OT can be used as an ultra sensitive force measurement tool to study interactions involving very small forces. We use a double tweezers to perform ultra sensitive measurement of the force due to the scattering of light as a function of its wavelength, in other words, to perform a Force Spectroscopy. Our results show not only the Mie resonances but also a selective coupling to either the TE, TM or both microsphere modes using the light polarization and the beam positioning. Mie resonances have usually been observed by scattering measurements. Very few reports of levitation experiments observed these resonances directly through the force. The double tweezers system has the advantage and flexibility of a stable restorative force measurement system. The experimental results show excellent agreement with Gaussian shaped beam partial wave decomposition theory. The understanding of the optical scattering forces in dielectric microspheres under different incident beam conditions is important as they have been used as the natural force transducer for mechanical measurements. Our results show how careful one has to be when using optical force models for this purpose. The Mie resonances can change the force values by 30-50%. Also the results clearly show how the usually assumed azimuthal symmetry in the horizontal plane no longer holds because the beam polarization breaks this symmetry.
The objective of this research is to use the displacements of a polystyrene microsphere trapped by an optical tweezers (OT) as a force transducer in mechanical measurements in life sciences. To do this we compared the theoretical optical and hydrodynamic models with experimental data under a broad variation of parameters such as fluid viscosity, refractive index, drag velocity and wall proximities. The laser power was measured after the objective with an integration sphere because normal power meters do not provide an accurate measurement for beam with high numerical apertures. With this careful laser power determination the plot of the optical force (calculated by the particle displacement) versus hydrodynamic force (calculated by the drag velocity) under very different conditions shows an almost 45 degrees straight line. This means that hydrodynamic models can be used to calibrate optical forces and vice-versa. With this calibration we observed the forces of polystyrene bead attached to the protozoa Leishmania amazonensis, responsible for a serious tropical disease. The force range is from 200 femto Newtons to 4 pico Newtons and these experiments shows that OT can be used for infection mechanism and chemotaxis studies in parasites. The other application was to use the optical force to measure viscosities of few microliters sample. Our result shows 5% accuracy measurements.
Furnas Centrais Elétricas S.A is one of the greatest companies of the Brazilian electric power sector and a pioneer in using infrared thermography. In the early 70s, the maintenance policy used was a centralized approach, with only one inspection team to cover all the company’s facilities. In the early 90s, FURNAS decided to decentralize the thermography inspections creating several inspection teams. This new maintenance policy presented several advantages when compared to the previous one. However the credibility of the results obtained with the thermal inspection was frequently being questioned, in part due to the lack of a detailed planning to carry out the transition from the centralized inspection to the decentralized one. In some areas of the company it was suggested the inactivation of the thermography. This paper presents the experience of FURNAS with these different maintenance policies and details the procedures which have been taken that nowadays the infrared thermal inspection has become one of the most important techniques of predictive maintenance in the company.
In the characterization of graded-index glass waveguides, use of the standard m-line method by several laboratories has produced increasing discrepancies in the refractive index profile with decreasing film depth. We have addressed this very critical problem by a direct near-surface (DNS) approach, where the polarimetric Abeles-Hacskaylo method was extended as an admittance-matching condition for inhomogeneous films. In this paper, we review the measurement procedures of the same Ag+-exchanged waveguides by the DNS approach and by the m-line method, whose result showed significant disagreement at the film-air interface. We search the underlying reasons for this disagreement and test them against non-optical measurements of the ion-concentration profile, to reach a better understanding of the near-surface region, as well as of the distinct probing range of the m-line and DNS techniques.
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