This PDF file contains the front matter associated with SPIE Proceedings Volume 10226, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

Recent results on the interaction of high power laser pulses with dielectrics containing metal nanoparticles are observed. The excimer laser pulse modification of copper nanoparticles synthesized by ion implantation in silicate glass are considered. Pulsed laser irradiation makes it possible to modify such composite layer, improving the uniformity in the size distribution of the nanoparticles. Changes induced by pulsed laser exposure suggest there are both reductions in average size of the metal nanoparticles, and some long-range dissolution of metal atoms in the matrix. Experimental data on laser modification are explained by photofragmentation of the nanoparticles in the dielectric matrix.

We present a theoretical and computational investigation of the possibility of achieving slow terahertz light by exploiting the tunneling induced transparency (TIT) effect in suitably engineered quantum well heterostructure devices. We design such a meta-material and show how TIT could lead to large values of the group refractive index, unfortunately at the cost of strong field attenuation due to decoherence. As a suitable alternative, we propose a grating, consisting of a buffer and a quantum cascade amplifier regions, arranged in such a way as to achieve slow light and simultaneously compensate for the large signal losses. Our calculations show that a binary message could be reliably transmitted through this system, with non-critical reduction of the signal to noise ratio, as we achieve a slow-down factor of more than 70.

The present work aims to further investigate the effects of laser cleaning of the burnt Parthenis' paintings, and to the development of a restoration procedure with the use of pulsed lasers, in combination with several characterisation methods. The evaluation of different types of laser, such as Nd:YAG laser with five harmonics, Er:YAG laser, and CO₂ using various fluences on different areas of the painting has been already performed and published1. In this work, and taking into account the previous results as well as the respective literature^{2, 3}, untreated parts of the burnt paintings were cleaned with the optimum combination of laser parameters. The cleaning process was thoroughly examined with X-ray diffraction (XRD). In addition, the stratified layers of the paint were determined giving valuable information about the inner layers of the paintings. In the previous published work¹, the optimum cleaning parameters have been assessed with the assumption that one single laser will be used to clean the entire surface of both burnt paintings. Nevertheless, thickness differences of the layers of the applied paint lead to the necessity of investigating the use of multiple lasers and of different parameters according to the required degree of cleaning. Therefore, restoration procedures based on multiple lasers or on a single laser, with varying parameters, are evaluated. One more technique to be introduced here is the visual digital reconstruction of the burnt paintings, which has the potential to provide an estimate of the degree of the required treatment.

Conservation of cultural heritage treasures is the most important issue for transferring knowledge to the public through the next generation of students, academics, and researchers. Although this century is authenticating e-books and information by means of electronic text, still historical manuscripts as content as well as objects are the main original recourses of keeping a record of this transformation. The current work focuses on cleaning paper samples by the application of pulsed light, which is interventional. Experiments carried out using paper samples that are artificially colonized with Ulocladium chartarum. Paper is treated by Nd:YAG laser light. The available wavelength is 1064 nm, at various fluences, repetition rates and number of pulses. Two types of paper are stained with fungi colonies, which grow on substrates of clean paper, as well as on paper with ink text. The first type of paper is Whatman No.1056, which is closer to pure cellulose. The second type of paper is a page of a cultural heritage book published in 1926. Cleaning is performed using laser irradiation, thus defining the damage threshold of each sample. The treatment on paper Watman showed a yellowing, especially on areas with high concentration of fungi. The second sample was more durable to the exposure, performing the best results at higher fluences. Eventually, the paper samples are characterized, with optical microscopy and SEM/EDX analyses, prior to and after cleaning.

Azopolymers are one of the most efficient types of media for recording the polarization state of light. An essential optical parameter to characterize them is the value of the birefringence Δn induced on illumination with polarized light. Laser beam is used as a pump and the birefringence is commonly probed by another laser with wavelength, different from the pump one. However, data about the spectral behavior of Δn are given rarely.

In this work we present experimental data for the dynamics of spectra of birefringence during illumination with pump lasers with wavelengths varying from 355 nm to 514 nm i.e. from the peak of absorbance to the edge of the absorbance band of the azopolymer used. Furthermore, we investigate the influence of nanoparticles from zinc oxide (ZnO) with different concentrations, incorporated in the azopolymer. The azopolymer used for this study is the water soluble poly[1- [4-(3-carboxy-4-hydroxyphenylazo)benzenesulfonamido]-1,2-ethanediyl, sodium salt], shortly denoted as PAZO. As indicated by our experiments, thin films from this azopolymer can be used for polarization diffractive elements, operating in the entire visible range of the spectrum.

The creation of microporous surface modification of chitosan thin films irradiated by ultrashort laser pulses are studied. For this purpose, chitosan substrates were treated by using an amplified Ti:sapphire laser system at 800 nm central wavelength with 30 fs and 150 fs pulse duration and repetition rate 1 kHz and 50 Hz, respectively. Formation of surface modifications for both cases (30 fs and 150 fs) after femtosecond laser irradiation were observed. The threshold values for single-pulse (N = 1) and multi-pulse (N > 1) modification were evaluated by studying the linear relationship between the squared crater diameter D² and the logarithm of the laser fluence (F) for N = 1, 2, 5, 10, 20, 30 and 50 number of laser pulses. The coefficient of incubation ξ, a major parameter in the process of surface modification and ablation of materials also was calculated for multi - pulse fluence threshold estimation by power - law relationship F_th (N) = F_th (1) N^ξ-1, where N is the number of applied laser pulses. The surface properties of chitosan based thin films before and after femtosecond laser irradiation were investigated. The aim of this work is to determine the optimal morphological characteristics of the created structures for tailoring of protein adsorption and cell behavior.

Azopolymers are well known organic materials for polarization holographic recording due to the induced anisotropy under illumination with polarized light. They possess all the desirable characteristics of the known polarization-sensitive materials, as high sensitivity and reversibility, but excel them substantially in the magnitude of the photoinduced birefringence. This makes possible to record reversible polarization gratings with high diffraction efficiency.

In this paper results of experimental investigations on the reversibility properties of birefringence photoinduced in azopolymers are reported, depending on the conditions of subsequent optical and thermal treatment. Thin films of different polymers were prepared in order to examine the kinetics of multiple recording and erasure of birefringence in different types of azopolymers. The reversibility of the polarization recording has been studied using two different method of erasure – by increased temperature and on illumination with circularly polarized light.

The experimental and theoretical investigations of the optical characteristics of laser nanostructured Ag nanoparticles (AgNPs) in ZnO medium are of particular interest for this study. The Ag-ZnO nanocomposites are fabricated by room temperature pulsed laser synthesis method. Ag nanoparticles are prepared by laser deposition and subsequent laser annealing of silver thin film. Laser annealing of silver layer is performed at second and third harmonics of the Nd:YAG laser. The morphology of AgNPs differs significantly after the UV and VIS surface modification. The morphology and optical properties of the samples are studied according to the annealing regimes. A comparative study of the measured plasmon resonance properties with the theoretical calculations of the extinction efficiency by generalized multiparticle Mie (GMM) method is carried out. The extinction spectrum is determined as a function of the nanoparticles size distribution and the surrounding ZnO medium. The electromagnetic field intensity enhancement realized in the “hot spots” of AgNPs leads to substantial enhancement of the near band-edge UV photoluminescence (PL) emission of ZnO nanostructures and attenuation of the defect-related deep-level VIS PL signal after annealing at 355 nm and 532 nm.

In present days graffiti is a common problem that many restorers have to deal with due to both its unaesthetic appearance and damaging nature for the surface beneath. We report laser cleaning of graffiti paints (black, white, blue, green and red) on limestone and granite. The efficiency of two laser systems is compared: high repetition rate (20 kHz) Copper Bromide Vapor Laser (CuBrVL) generating wavelength 510.6 nm and low repetition rate (up to 10 Hz) Q-switched Nd:YAG laser generating fundamental wavelength 1064 nm and its second harmonic 532 nm. The surface condition of the stone samples before and after cleaning is evaluated by means of optical microscopy. On that base, suitable working parameters are chosen in order to avoid under- or over-cleaning.

In this work laser-assisted methods for metal nanostructures formation and their application as active substrates in Surface Enhanced Raman Spectroscopy are presented. The nanostructures are fabricated by laser processing of gold thin films deposited on low cost substrates as glass, ceramic, polymer and paper. The films are deposited by classical PLD technology. The produced films are then processed by nanosecond pulses delivered by nanosecond Nd:YAG laser system. At certain conditions the laser treatment leads to formation of discrete nanostructure on the substrate surface. Femtosecond Pulsed Laser Deposition in air is also applied for direct deposition of gold nanostructure. In another set of experiments gold nanoparticle colloids are fabricated by laser ablation of gold target in chloroform. The fabricated structures are then tested as active systems in SERS, as detection of pesticides (DDT), nitrates (NH₄NO₃), and drugs (Methylene blue) is demonstrated. The obtained results show that these nanostructures can be efficiently used in the detection and monitoring of materials with a high social impact.

Nanosecond pulsed laser ablation of a Ag target in water was applied to prepare noble metal nanoparticles. The fundamental (λ = 1064 nm) wavelength and the second harmonic (λ_SHG = 532 nm) of a Nd-YAG laser system were used for the fabrication procedure. The effect of the liquid level over the target surface on the characteristics of the nanoparticles was investigated using four different values (5, 8, 16, 29 mm). The liquid volume was constant and the duration of the ablation process was 5 min. A second set of experiments were aimed at clarifying the influence of the duration of ablation. The process was interrupted after 5, 10, 15, 20, 25 min and the mass concentration of Ag in the colloid was measured. This enabled us to establish the dependence of the mass concentration of the Ag on the duration of ablation. The profile of the optical extinction spectra of the colloids was helpful in assessing the state of the solid phase and the morphology of the material. Images obtained by transmission electron microscopy were used to visualize the morphology of the nanostructures produced.

The residual stress and microstrain distribution induced by laser beam welding of the low-alloyed C45 steel plate was investigated using high-resolution time-of-flight (TOF) neutron diffraction. The neutron diffraction experiments were performed on FSD diffractometer at the IBR-2 pulsed reactor in FLNP JINR (Dubna, Russia). The experiments have shown that the residual stress distribution across weld seam exhibit typical alternating sign character as it was observed in our previous studies. The residual stress level is varying in the range from -60 MPa to 450 MPa. At the same time, the microstrain level exhibits sharp maxima at weld seam position with maximal level of ∼4.8·10^-3. The obtained experimental results are in good agreement with FEM calculations according to the STAAZ model. The provided numerical model validated with measured data enables to study the influence of different conditions and process parameters on the development of residual welding stresses.

Fabrication of silver nanoparticle colloids using nanosecond pulsed laser ablation in liquid is studied. Laser ablations of silver target in chloroform, toluene and ethanol were performed to prepare different nanosize metal colloids. Both fundamental wavelength (1064 nm) and second harmonic (532 nm) of Nd: YAG laser system were used. The influence of the laser wavelength on the morphology, size distribution, shape and optical properties of the produced nanoparticles was studied by transmission electron microscopy (TEM) and UV-Visible absorption measurements. The selected area electron diffraction (SAED) was employed to identify the phase composition of the formed nanostructures. Nanoparticles in chloroform show a large difference in the mean size at both laser wavelengths used — 3,2 nm at 1064 nm and 43 nm at 532 nm. The laser ablation in toluene at both laser wavelength used results in formation of nanoparticles with relatively small mean size (up to 5 nm). Silver nanoparticles in ethanol produced by 1064 nm show mean size of 20 nm while those prepared by second harmonic — 45 nm. The nanoparticles produced by ablation in chloroform and toluene do not show surface plasmon resonance (SPR) absorption in their optical absorption spectra. In contrast the colloidal nanoparticles produced by laser ablation in ethanol exhibit plasmon behavior. The presented method is an alternative to the widely used chemical methods for the preparation of colloidal solutions with certain characteristics enabling their application in the printed electronics to obtain the conductive tracks, and also for the preparation of nanostructured surfaces for surface-enhanced Raman spectroscopy (SERS).

Results on fabrication of Au nanostructures by laser ablation in open air are presented. The ablation of the Au target is performed in air environment by nanosecond laser pulses delivered by Nd:YAG laser system operated at λ = 355 nm. Due to the high density of the ambient atmosphere, the intensive collisions of the plume spices result in formation of nanoparticles and aggregates by condensation close to the target. The produced nanoagregates are deposited on a quartz substrate where grow in a specific nanostructure. Diagnostics of the laser-generated plasma for the laser fluences used in this study is performed. Study based on change of ambient conditions shows that the increase of the air pressure from 10 Torr to atmospheric one leads to transition from thin film to porous structures. It is found that the surface morphology of the structures produced by pulsed laser deposition (PLD) in open air strongly depends on the substrate-target distance. The electrical properties of the obtained structures are studied by measurement of their electrical resistance. It is found that the conductivity of the structures strongly depends on their morphology. The fabricated structures have potential for application in the field of electronics and sensors.

Recently, an intensive research is carried out on plasmonic structures due to their potential application in many areas such as sensing, light harvesting and energy conversion and storage. In particular, a growing interest is observed in the Nanoparticle Over Mirror (NOM) structures for which the lithography and surface chemical functionalization represent the most popular production routes¹. However, the application of those techniques is limited by the low efficacy, process complexity and chemical contamination of nanoparticles (NP). In this work, we report the contamination-free and low cost fabrication method of NOMs based on wet coating and ultrasonic-assisted nanocolloid drying process. The glass plates covered with magnetron sputtered 100 nm thick Au film and subsequently with Al₂O₃ layers (6 – 36 nm) by means of pulsed laser deposition are used as substrates. Au NPs are produced in the form of colloidal suspension by means of laser ablation in water using the 1064 nm, 6 ns Nd:YAG laser. The NOM synthesis is finalized by imposing of the Au NP suspension onto the as prepared Au-Al₂O₃/glass substrates and dried. To avoid NP agglomeration, the wet coated substrates are sonicated using 20W, 20 kHz ultrasound generator. SEM inspection of the obtained NOM structures confirms the positive sonication effect, i.e. the presence of agglomerate-free, homogenous layers. These consist of NPs (36 nm average diameter) which are characterized by the resonance absorption band at 528 nm. For NOM structures the UV-vis spectra reveal increased infrared activity and peak shift in agreement with theoretical modeling². The NOM structure characterization is completed by analysis of the SEM and profilometry measurement results.

In the present work, we report on the analysis of archaeological metal artefacts from Late Bronze Age, performed by means of Laser Induced Breakdown Spectroscopy (LIBS). The experiment was carried out at ambient air and at 1064 nm of a Nd:YAG laser with pulse durations of 10 ns and energy of 10 mJ. The analytical information obtained by LIBS spectra was used for qualitative determination of the elements in the material used for manufacturing of the investigated objects. Quantitative estimation of the elemental concentration of tin and lead in the bulk of the samples was done after generating calibration curves for a set of four standard samples with a wide range of tin and lead concentrations and with similar matrix composition. The preliminary results of the qualitative and the quantitative analyses gave indications about the manufacturing process of the investigated objects and for their provenance as well.

High intensity energy fluxes, such as electron beams and laser beams are widely used for surface alloying of metals and alloys. These technologies are able to cause the formation of the so called melt pool where the alloying elements interact each other. It is known that the homogenization of the surface alloy can be explained by intense Marangoni convection, caused by the high temperature gradient in the melt pool. The convection is inversely to the speed of the specimen motion during the alloying process and therefore, the choice of low alloying velocity will reflect on more homogeneous structure of the obtained alloy. In this study, a comparison of the structure and properties of electron and laser beam surface alloying of aluminium with niobium was conducted. The phase composition of the alloyed layers was determined by XRD (X-ray diffraction) with CuKα radiation. The microstructure was studied by SEM (Scanning Electron Microscopy). Chemical analysis was carried out using an EDX electron probe microanalyser. The microhardness of the obtained samples is also measured and compared with respect to the technology of the formation of each surface alloy.

Thiogallate compounds represented by general formula MGa₂S₄ [where M- Ca⁺², Ba⁺², Sr⁺², Pb⁺², Eu⁺², Eu⁺³, (Na⁺¹La⁺³) and (Na⁺¹Ce⁺³)] are highly effective electro-luminescence and laser materials. These materials were first synthesized in 1971 and studied by many groups due to their possible applicability in opto-, and quantum- electronics. Forbidden band gap (ΔE) at room temperature (RT) for these materials varies in a wide range from ΔE ∼ eV for CaGa₂S₄ to ∼ 2.32 eV for Ca₄Ga₂S₇.

In the present paper the results of structural properties and photoluminescence (PL) measurements (temperature range of 77 – 300 K) of melt grown Ca₄Ga₂S₇ single crystals doped with 5 at% of rare earth (RE) Eu²⁺ (Ca₄Ga₂S₇ : Eu²⁺) are described for the first time. It is shown that, broadband PL with a maximum at 660 nm is caused with intra shell transitions 4f⁶5d - 4f⁷(⁸S_7/2) of Eu²⁺ ions.

COSMA: Coherent Optics Sensors for Medical Application is an European Marie Curie Project running from 2012 to March 2016, with the participation of 10 teams from Armenia, Bulgaria, India, Israel, Italy, Poland, Russia, UK, USA. The main objective was to focus theoretical and experimental research on biomagnetism phenomena, with the specific aim to develop all-optical sensors dedicated to their detection and suitable for applications in clinical diagnostics. The paper presents some of the most recent results obtained during the exchange visits of the involved scientists, after an introduction about the phenomenon which is the pillar of this kind of research and of many other new fields in laser spectroscopy, atomic physics, and quantum optics: the dark resonance.

We report the first observation of sub-natural-width dark resonances of enhanced transparency on the D² line of potassium, contained in an optical cell with reduced (8mm) dimensions and buffered by 30Torr of Ne. The Potassium vapours are irradiated by a frequency modulated DFB diode laser light (with λ = 766.7nm and 2MHz bandwidth), and are placed in orthogonal to the light magnetic field scanned around zero value. Very good signal-to-noise ratio and narrow (∼20kHz) dark resonances are observed and studied in unshielded laboratory environment. The dark resonance formation is related to coherent superposition of the ground-state Zeeman sublevels by respective components of the frequency-modulated light.

The fluorescence and non-linear absorption spectra of Cs¹³³ vapour in an extremely thin cell were calculated by using the perturbation theory with respect to the pumping field intensity. The problem of the atoms’ non-linear polarization was solved for arbitrary values of the total momenta of the resonance levels pumped by a linearly-polarised laser field. It was demonstrated that the spontaneous emission from the upper level affects the amplitude and sign of the lower level longitudinal alignment and results in a change of the amplitude and sign of the non-linear absorption resonance at the closed transition. The comparison of the numerical calculations with the experimental data for the D₂ line of ¹³³Cs shows a very good agreement.

Due to their broad spectral bandwidth and superior temperature performance, resonant phonon quantum cascade laser (QCL) designs have become the active-region of choice for many of the leading groups in terahertz (THz) QCL research. These gain media can vary substantially in the number of wells and barriers as well as their corresponding thicknesses, but all such structures employ a common resonant phonon lower laser level depopulation scheme and a resonant tunneling mechanism for efficient current injection into the upper laser level. The presence of a strong anticrossing between the injector and upper laser level leads, under the right conditions, to a pronounced splitting of the emission spectra into high and low frequency lobe components around some central transition frequency. This spectral hole burning effect also manifests itself in the time domain as a form of pulse switching between signals corresponding to the two lobes of the split gain, as it has already been experimentally observed. This process was termed as a form of temporal hole burning (THB), which next to spectral and spatial hole burning, completes the plethora of dynamic "hole burning" phenomena encountered in QCLs. In this work, we investigate the temporal dynamics of THz QCLs with a strong injector anticrossing via numerical solution of the Maxwell-Bloch laser equations. Our simulation results show remarkable agreement with experiment and we further outline the development of a theoretical model which intuitively explains this effect.

In the present work we investigate the relation of the polarization moments having different ranks with the tensor components which form the observable integral CPT signal, in the presence of a stray magnetic field. A numerical experiment with parameters close to the real ones is performed, using a program based on the irreducible tensor operator formalism¹. The integral fluorescent signal is calculated for the non-polarized fluorescence at different laser power excitation. Detailed analysis of the numerical solutions for all tensor components which describe population and alignment allows visualizing the dynamics of their behavior in dependence on the experimental geometry and laboratory magnetic field B′. The dependence of population f₀⁰, longitudinal f₀² and transverse f₂² alignment in the presence of transverse magnetic field is investigated. The shape and sign of the resonance change with laser power.

In this paper we have demonstrated coherent population trapping and Rydberg state excitation in the five level media. We have analysed the influence of non zero multiphoton detunings and the self-phase modulation on these processes.

We have studied the propagation of light in M- and W-systems, and have demonstrated the possibility of such propagation with nonlinear group velocity being either less than (slow light) or greater than (superluminal propagation) of the speed of light in vacuum without being distorted.

Dynamic laser speckle analysis is non-destructive detection of physical or biological activity through statistical processing of speckle patterns on the surface of diffusely reflecting objects. This method is sensitive to microscopic changes of the surface over time and needs simple optical means. Advances in computers and 2D optical sensors forced development of pointwise algorithms. They rely on acquisition of a temporal sequence of correlated speckle images and generate activity data as a 2D spatial contour map of the estimate of a given statistical parameter. The most widely used pointwise estimates are the intensity-based estimates which compose each map entry from a time sequence of intensity values taken at one and the same pixel in the acquired speckle images. Accuracy of the pointwise approach is strongly affected by the signal-dependent nature of the speckle data when the spread of intensity fluctuations depends on the intensity itself. The latter leads to erroneous activity determination at non-uniform distribution of intensity in the laser beam for the non-normalized estimates. Normalization of the estimates, introduces errors. We propose to apply binarization to the acquired speckle images by comparing the intensity values in the temporal sequence for a given spatial point to the mean intensity value estimated for this point and to evaluate a polar correlation function. Efficiency of this new processing algorithm is checked both by simulation and experiment.

Three new conical intersections S₀/S₁ (cis-anti, trans-syn and trans-anti) were fond which mediate the processes of photo-induced formation of cyclobutane thymine dimers. Their structures were optimized at the CASSCF(2,2) (Complete Active Space Self Consistent Field method) level of theory with the minimal bases set STO-3G*. The geometries were explored with respect to their structural and electron features. The found conical intersections S₀/S₁ give a clear indication that they could be included in the internal conversions of the ¹ππ^* excited states of the stacked dimers to cyclobutane photodimers and vice versa.

The paper presents lecture materials given at the Nineteenth International Conference and School on Quantum Electronics “Laser Physics and Applications” (19th ICSQE) in 2016, Sozopol, Bulgaria and contains the results of the 10-year research of Belarusian Antarctic expeditions to study the atmospheric aerosol and Earth surface in Antarctica. The works focus on the studying variability and trends of aerosol, cloud and snow characteristics in the Antarctic and the links of these processes with the long range transport of atmospheric pollutants and climate changes.

This is an overview of the development and the applications of compact elastic backscatter depolarisation lidars. Two of such sensors are installed on-board the high-altitude research aircraft Myasishchev M-55 Geophysica. The installation of the lidars is intended for simultaneous probing of air parcels respectively upward and downward from the aircraft flight altitude to identify the presence of clouds (or aerosol )above and below the aircraft and to collocate them with in situ instruments. The lidar configuration and the procedure for its on-ground validation is outlined. Example of airborne measurements include polar stratospheric clouds, both synoptic and in lee-waves, ultra-thin cirrus clouds around the tropical tropopause and observation of aerosol layers emerging from the top of deep tropical convection. One unit is realized for groundbased application and is extensively used in campaigns and routine measurements of the MLH variation and aerosol backscatter in the lower troposphere.

Laser monitoring (remote sensing) may be considered as the science of collecting and interpreting information about the atmosphere, earth and sea using sensors on earth, on platforms in our atmosphere (airplanes, balloons) or in space (satellites) without being in direct physical contact with them. Remote sensing by LIDARs (Light Identification Detection and Ranging) has wide applications as technique to probe the Earth's atmosphere, ocean and land surfaces.

LIDARs are widely used to get knowledge of spatial and temporal variations in meteorological quantities (e.g. temperature, humidity, clouds and aerosol properties) and to monitor the changes in these quantities on different timescales.

Subject of the present work is quite wide. It is rather difficult to perform analysis and to provide full knowledge about existing information. In the present work, in addition to the literature data, the information will be provided also about KA-09 aerosol LIDAR developed at the Marmara Research Centre of TÜBITAK (Turkish Scientific and technological Research Council) and also about KA-14 LIDAR developed at the National Aviation Academy of Azerbaijan for remote sensing of contaminations on water surfaces taking place during oil-gas production. The main goal of this paper is to give students insight in different remote sensing instruments and techniques (including their perspectives) that are used for the derivation of meteorological quantities and obtaining the information about water surface.

A new laser induced fluorescence (LIF) KA-14 LIDAR (Light Identification Detection and Ranging) system for detecting of oil spills on the sea surface was developed and employed at the National Aviation Academy of Azerbaijan. Laser’s parameters used in LIDAR are as follows: •laser CFR 200- type QUANTEL, λ = 355 nm, beam ∅ = 5.35 mm, f = 20 Hz, pulse duration and power τ = 7 ns and 60 mJ, respectively.

The first results of measurements in the laboratory and the results of measurements at natural environment from distances up to ∼ 200 m revealed perspectives for using this LIDAR for detection of oil contaminations on sea as well as on earth surfaces (these measurements have been performed at Pirallahi Oil-Gas Production Company, Absheron peninsula, Baku, Azerbaijan).

In the present work the results of emission spectra of crude oils taken from different regions of Absheron peninsula as well as the emission spectra of the oil spills on the surface of Caspian sea will be reported and discussed. These measurements open perspectives for using developed LIDAR for determination of place of oil-gas production company from which leakage takes place.

Durable aerosol/dust loadings affecting the atmosphere over the city of Sofia, Bulgaria (42.65 N, 23.38 E) were monitored by a Nd:YAG-laser-based lidar, from April to July 2009. The events lasted almost throughout the entire period. This study is only focused on the experimental results obtained on 15 and 23 April, when extraordinary in altitude (up to 15 km) aerosol layers were detected. For the two days, Dust Regional Atmospheric Model, provided by the Barcelona Super-Computing Center, had forecast Saharan dust incursions over Bulgaria. The origin of the aerosol layers detected by the lidar was identified using the Hybrid Single-Particle Lagrangian Integrated Trajectory model for calculations of the backward air-mass trajectories. The results of measurements are presented in terms of time-averaged vertical profiles of the atmospheric backscatter coefficient and color maps in height-time coordinates, which illustrate the aerosol-mass spatial distribution and its temporal evolution, within the stable layers registered. Retrieved profiles at the two lidar wavelengths (532 nm and 1064 nm) are used to calculate the corresponding profiles of the backscatter-related Ǻngström exponent as a qualitative indicator of the dominant aerosol particle size fractions in the layers observed.

Presented are results of lidar measurements and characterization of wildfire caused smoke aerosols observed in the atmosphere above the city of Sofia, Bulgaria, related to two local wildfires raging in forest areas near the city. A lidar systems based on a frequency-doubled Nd:YAG laser operated at 532 nm and 1064 nm is used in the smoke aerosol observations. It belongs to the Sofia LIDAR Station (at Laser Radars Laboratory, Institute of Electronics, Bulgarian Academy of Sciences), being a part of the European Aerosol Lidar Network. Optical, dynamical, microphysical, and geometrical properties and parameters of the observed smoke aerosol particles and layers are displayed and analyzed, such as: range/height-resolved profiles of the aerosol backscatter coefficient; integral aerosol backscattering; sets of colormaps displaying time series of the height distribution of the aerosol density; topologic, geometric, and volumetric properties of the smoke aerosol layers; time-averaged height profiles of backscatter-related Ǻngström exponent (BAE). Obtained results of retrieving and profiling smoke aerosols are commented in their relations to available meteorological and air-mass-transport forecasting and modelling data.

The sensing laser radiation wavelength is one of the most significant factors conditioning the elastic lidar efficiency. Nevertheless, its role in the process of lidar sensing has not been investigated systematically so far. Therefore, the main purpose of the present work is to develop and perform an initial examination of an approach to solve this problem based on modeling the profile of the lidar return signal (the lidar profile) and evaluating, in a specific way, the corresponding profile of the measurement signal-to-noise ratio (SNR). The measurement fluctuations are considered as mainly due to the Poisson shot noise that is intrinsic to the dark current and the photocurrent induced by the useful signal itself and the atmospheric background. The initial results obtained show for instance that for ground-based lidar facilities the maximum Rayleigh return signal is obtainable at wavelengths about 350nm. The roles are changed when sensing clouds using wavelength from 400nm to 1000-2000nm. Then, the longer wavelengths provide higher return power from clouds, and the effect is magnified in aerosol-loaded (and especially hazy) atmosphere. The results of such investigations are useful when selecting optimal lidar-design characteristics ensuring maximum brightness and contrast of the lidar-acquired images of specific aerosol strata and objects in the atmosphere.

A study of the atmospheric boundary layer (ABL) height and its relation to the variations in the aerosol optical depth (AOD), Ångström coefficients, water vapor column (WVC) and total ozone column (TOC) was carried out in June 2011 and June 2012 at three sites in the city of Sofia (Institute of Electronics, Astronomical Observatory in the Borisova Gradina Park and National Institute of Geophysics, Geodesy and Geography). A ceilometer CHM15k, a sun photometer Microtops II, an ozonometer Microtops II and an automatic meteorological station were used during the experiments.

Measurements of the AOD, WVC and TOC were done during the development of the ABL (followed by the ceilometer). In order to access microphysical properties of the aerosols, the Ångström coefficients α and β were retrieved from the spectral AOD data by the Volz method from three wavelength pairs 500/1020nm, 500/675nm and 380/1020nm. Comparison was done between the results obtained. Daily behavior of the AOD, Ångström exponent α and turbidity coefficient β, WVC and TOC are presented. Different types of AOD and WVC behavior were observed. The AOD had maximum values 1-2 h before ABL to reach its maximum height for the day. No significant correlation is found between TOC daily behavior and that of the AOD and WVC.

The spectral range of 0.85 - 0.9μm wavelengths utilized by laser diode (LD) technology contains a relatively intensive spectrum of third rovibrational overtone of the water molecule, pure of interfering spectra of the other major atmospheric gases. We developed a spectroscopic application of pulsed 100W LDs generally limited by their broad, multimode laser line. In fact, their powerful laser radiation propagating in the atmosphere is modulated significantly by multiple resonance absorption lines. The magnitude of the integral absorption pattern is assessed combining theoretical and experimental calibration and using HITRAN database. The resultant absorption spectrum is found to be unsaturated, providing a great dynamic range of measurement of atmospheric humidity within 15% random error of lidar returns ranging to 2km. The reported DIAL technique which utilizes the advantage of direct detection of the lidar profiles and simple operation is prospective for the framework of atmospheric and climatic monitoring.

This paper reviews recent progresses in ultrafast laser-based X-ray sources and their potential applications to high throughput X-ray imaging. Prospects for the utilization of X-rays sources related to the Laser Wakefield electron Acceleration (LWFA) are more specifically discussed with emphasis on application in diagnostic radiology.

As one of the major health problems for mankind is cancer, any development for the early detection and effective treatment of cancer is crucial to saving lives. Worldwide, the dream for the anti-cancer procedure of attack is the development of a safe and efficient early diagnosis technique, the so called “optical biopsy”. As early diagnosis of cancer is associated with improved prognosis, several laser based optical diagnostic methods were developed to enable earlier, non-invasive detection of human cancer, as Laser Induced Fluorescence spectroscopy (LIFs), Diffuse Reflectance spectroscopy (DRs), confocal microscopy, and Optical Coherence Tomography (OCT). Among them, Optical Coherence Tomography (OCT) imaging is considered to be a useful tool to differentiate healthy from malignant (e.g. basal cell carcinoma, squamous cell carcinoma) skin tissue. If the demand is to perform imaging in sub-tissular or even sub-cellular level, optical tweezers and atomic force microscopy have enabled the visualization of molecular events underlying cellular processes in live cells, as well as the manipulation and characterization of microscale or even nanoscale biostructures. In this work, we will present the latest advances in the field of laser imaging and manipulation techniques, discussing some representative experimental data focusing on the 21th century biophotonics roadmap of novel diagnostic and therapeutical approaches. As an example of a recently discussed health and environmental problem, we studied both experimentally and theoretically the optical trapping forces exerted on yeast cells and modified with estrogen-like acting compounds yeast cells, suspended in various buffer media.

Plum pox virus (PPV) is among the most studied viral diseases in the world in plants. It is considered to be one of the most devastating diseases of stone fruits in terms of agronomic impact and economic importance. Noninvasive, fast and reliable techniques are required for evaluation of the pathology in selection trees with economic impact. Such advanced tools for PPV detection could be optical techniques as light-induced fluorescence and diffuse reflectance spectroscopies. Specific regions in the electromagnetic spectra have been found to provide information about the physiological stress in plants, and consequently, diseased plants usually exhibit different spectral signature than non-stressed healthy plants in those specific ranges.

In this study spectral reflectance and chlorophyll fluorescence were used for the identification of biotic stress caused by the pox virus on plum trees. The spectral responses of healthy and infected leaves from cultivars, which are widespread in Bulgaria were investigated. The two applied techniques revealed statistically significant differences between the spectral data of healthy plum leaves and those infected by PPV in the visible and near-infrared spectral ranges. Their application for biotic stress detection helps in monitoring diseases in plants using the different plant spectral properties in these spectral ranges. The strong relationship between the results indicates the applicability of diffuse reflectance and fluorescence techniques for conducting health condition assessments of vegetation and their importance for plant protection practices.

The skin neoplasias are on a second place in the world statistics of cancer incidence, and gastrointestinal tract (GIT) tumours are also in the “top ten” list. For the most of cutaneous and gastrointestinal tumours could be obtained better prognoses for patients, if an earlier and precise diagnostics procedure is applied. One of the most promising approaches for development of improved diagnostic techniques, is based on optical detection, and analysis of the signatures of biological tissues for detecting the presence of pathological alterations in the investigated objects.

It is important to develop and combine novel diagnostic techniques for an accurate early stage diagnosis to improve the chances for skin and GIT tumours treatment. Optical techniques are very promising methods for such noninvasive diagnosis of skin and mucosa tumours, possessing the advantages of deep imaging depth, high resolution, fast imaging speed, and noninvasive character of detection. In this study we combine autofluorescence spectroscopy and optical imaging techniques to develop more precise evaluation of the tissue pathologies investigated.

We obtain chromophore maps for GIT and cutaneous samples, with better visualization of the tumours borders and margins. In addition, fluorescence spectra give us information about the early changes in chromophores’ contents into the tissues during neoplasia growth.

The carious decay develops a tiny area of demineralization on the enamel, which could be detected by element analytic techniques such as laser-induced breakdown spectroscopy (LIBS). That demineralization can quickly turn into a large lesion inside the tooth, it is often discovered too late to prevent the kind of decay that leads to cavities. The same optical LIBS detection approach could be used for monitoring of the caries removal using laser ablation or drilling techniques. For LIBS measurements we applied LIBS 2500Plus (Ocean Optics Inc., Dunedin, USA) system, which consists of seven spectrometric channels, covering spectral region from 200 to 980 nm, which optical resolution 0,05 nm, the spectrometers are connected with sample fiber bundle for 7-channels spectral system to the chamber for solid and liquid samples, Q-switched Nd:YAG laser, at 1 064 nm, with energy per pulse - 40 mJ, which is applied to induce plasma in the samples. LIBS spectra were obtained after single shot of the laser in the region of pathology. Samples investigated by LIBS are extracted teeth from patients, with periodontal problems on different stage of carious lesions, and their LIBS spectra are compared with the LIBS signals obtained from normal enamel and dentine tissues to receive complete picture of the carious lesion development. The major line of our investigations is related to the development of a methodology for real-time optical feedback control during selective ablation of tooth tissues using LIBS. Tooth structures, with and without pathological changes, are compared and their LIBS element analysis is used to differentiate major changes, which occur during tooth carious process and growth.

The standard procedure for cancer detection includes rigorous biopsy protocols, which are costly and time consuming; also the accuracy of the current diagnostic procedure relays entirely on the physician’s experience and it is limited by the high probability of miss rates. Therefore new sensitive diagnostic modalities for analysis of biopsy tissue samples or on site, in vivo microscopy tissue examination, are necessary.

In this study we present an investigation using nonlinear microscopy techniques for histological sections from biopsy tissue samples analysis. The samples were routinely processed for histological analysis and during the standard sampling the tissue slices were stained with hematoxylin and eosin dyes.

The application of nonlinear microscopy techniques, such as two photon excitation fluorescence microscopy and second harmonic generation microscopy in biomedical research for cancer diagnosis has been vastly expanding in the last few years. Two-photon excitation fluorescence microscopy is based on a non-linear optical effect of simultaneously absorption of two photons, thus achieves excited state of the absorbing molecule with energy corresponding to the sum of the energies of two incident photons. This method allows for using an excitation wavelength which is double the typically required one for excitation of diagnostically valuable endogenous fluorophores. This results in more efficient depth penetration of the longer wavelength light in the tissue. The second harmonic generation microscopy is based on the principle of the non-linear susceptibility in noncentrosymmetric structures; such structures in the tissue are formed mainly by the collagen fibers. After excitation with near-infrared photons with wavelength λ of the collagen structures, photons with wavelength ½ λ are emitted — this corresponding to the second harmonic of the excitation beam’s frequency.

The applied nonlinear microscopy techniques are suitable for detection and quantification of the morphological changes associated with stroma and epithelial transformation in colon cancer, providing complementary information about the tissue microstructure and displaying distinctive patterns between normal and malignant human colon tissues.

The wide spread of colorectal cancer and high mortality rate among the patients, brings it to a level of high public health concern. Implementation of standard endoscopic surveillance proves to be effective for reduction of colorectal cancer patients’ mortality, since its early diagnosis allows eradication of the disease prior to invasive cancer development, but its application in common clinical practice is still limited. Therefore the development of complimentary diagnostic techniques of the standard white-light endoscopy is on high demand. The non-invasive and highly informative nature of the fluorescence spectroscopy allow to use it as the most realistic prospect of an add-on “red flag” technique for early endoscopy detection of colorectal cancer.

Synchronous fluorescence spectroscopy (SFS) is a steady-state approach that is used for evaluation of specific fluorescence characteristics of cancerous colorectal tissues in our studies. The feasibility of polarization fluorescence technique to enhance the contrast between normal and cancerous tissues was investigated as well. Additional linear polarizing optics was used on the way of the excitation and emission fluorescence light beams. The polarizing effects were investigated in parallel and perpendicular linear polarization modes respectively. The excitation applied was in the region of 280 – 440 nm, with 10 nm scanning step, and the fluorescence emission was detected in the region of 300 – 800 nm.

Our previous experience with SFS technique showed its great potential for accurate, highly sensitive and specific discrimination between cancerous and normal colorectal tissue. Since one of the major sources of endogenous fluorescence with diagnostic meaning is the structural protein — collagen, which is characterized with high anisotropy, we’ve expected and observed an enhancement of the spectral differences between cancerous and normal colorectal tissue, which could be beneficial for the colorectal tumour’ diagnostics using SFS.

The paper presents our results on the study of the efficiency of inter-fractional changes in hemoglobin molecules depending on the laser radiation parameters. The evaluation of the quantum efficiency of light interaction in vivo with oxyhemoglobin (HbO2) and carboxyhemoglobin (HbCO) in the blood at wavelengths for 525 and 605 nm is presented. The photodissociation yield of 11% for HbO₂ and 79% for HbCO are measured at the wavelength of 525 nm and 10 % for HbO₂ and 76 % for HbCO at a wavelength of 605 nm. Thus, the quantum yield of photodissociation of the HbCO is considerably higher, which ensures high efficiency of photodecomposition of the HbCO in the blood. The obtained results can be used in the clinical phototherapy practice for effective treatment of CO poisoning.

The results of in vivo investigation of combined optical and ultrasound methods of tissue oxygenation and their application in medicine are presented. The optical method is based on the phenomenon of laser-induced photodissociation of blood oxyhemoglobin in cutaneous blood vessels. It is shown that this method provides an extraction of additional oxygen directly in the irradiation zone. The acoustic method enhances the efficiency of optically induced tissue oxygenation by improvement in the blood microcirculation. Some biomedical applications of the developed combined opto-ultrasound method of tissue oxygenation are discussed.

Experimental measurements and theoretical description have been performed of the spatial intensity distribution of the backward radiative response of tissue-like Intralipid-20% dilutions in distilled water irradiated by a collimated near-infrared cw laser beam. The investigations performed are a first step toward a complete estimation of the feasibility and potentialities of a stationary one-sided linear-strategy biomedical tomography approach to detecting characteristic inclusions (inhomogeneities, say ill places) in homogeneous highly-scattering host media (healthy tissues). The experimental results obtained are in good agreement with the derived theoretical expressions that thus would be of importance for the development and numerical modeling of stationary tomography algorithms ensuring optimally accurate data processing and interpretation.

One of the most widespread optical methods used in biophotonics is the pulse oximetry, which is based on the measurement of light-modulated pulse wave of blood. This is a non-invasive, objective method for evaluation of the blood supply. Recently it has become very popular in dental medicine for the measurement of the condition of pulp microcirculation. The aim of our research is to evaluate the possibilities of pulse oximetry for estimation the pulp microcirculation in intact teeth among young patients. Results obtained clearly show that this method can be applied to assess the pulp condition and could be used in clinical practice in combination with other diagnostic methods.

In this work we study the influence of the additional second-order dispersion introduced in sub-45 femtosecond laser pulses by intentional misaligning a folded 4-f otherwise dispersionless system. The theoretically calculated pulse durations are found to be in a good agreement with the respective experimental data from frequency-resolved optical gating measurements.

In last two decades the phenomena resulting from the evolution of ultra-short laser pulses in nonlinear dispersive medium actively are being studied. The most commonly used equation for describing the dynamics of optical pulses in one-dimensional and planar waveguides is the standard nonlinear Schrodinger equation (NSE). It works very well for nanosecond and picosecond laser pulses, but in the frames of femtosecond optics, it is necessary two additional terms to be included. They are responsible for higher order of linear dispersion and dispersion of nonlinearity. These effects are significant in the range of ultra-short light pulses. In the present paper, it is presented a theoretical model of the propagation of optical solitons. We found an exact analytical soliton solution of the modified NSE, including third order of linear dispersion and dispersion of nonlinearity. It is possible to observe a soliton as a result of the dynamic balance between effects of higher order of dispersion and nonlinearity.

In last two decades actively are studied the phenomena resulting from the evolution of ultrashort optical pulses in nonlinear dispersive media. The well-known (1+1D) nonlinear Schrödinger equation (NSE) describes very well the propagation of narrow-band optical pulses (Δω<<ω₀). Nowadays, it is quite easy to obtain broad-band phase-modulated femtosecond laser pulses or to reach the attosecond region where Δω≈ω₀. To explore their behavior it is necessary to use the more general nonlinear amplitude equation (NAE). In local time coordinate system it differs from the standard NSE with two additional non-paraxial terms. In present paper, by using the NAE, it is investigated the dynamics of higher order non-paraxial solitons. It is shown that the peak of soliton is linearly shifted in time domain. This temporal shift is observed in the frames of non-paraxial optics, even when the higher order nonlinear and dispersive effects are neglected.

We present experimental and theoretical investigation of the first picoseconds of formation of white continuum from 100 fs laser pulse in 0.5 cm BK7 glass. The theory gives an answer to the question of the physical mechanism of asymmetrical ultra-broadening of the pulses in the initial moment of filamentation. The spectra obtained from the experiment are compared with the spectrum profiles of the physical model and are in very good coincidence.

Powerful metal halide vapor lasers are excited with nanosecond pulsed longitudinal discharge in complex multicomponent gas mixtures. Using a new method, thermal conductivity of various 5- and 6-component gas mixtures is obtained under gas-discharge conditions, which are optimal for laser operation on the corresponding metal atom and ion transitions. Assuming that the gas temperature varies only in the radial direction and using the calculated thermal conductivities, an analytical solution of the steady-state heat conduction equation is found for uniform and radially nonuniform power input in various laser tube constructions. Using the results obtained for time-resolved electron temperature by measurement of electrical discharge characteristics and analytically solving steady-state heat conduction equation for electrons as well, radial distribution of electron temperature is also obtained for the discharge period.

Holography is defined as a two-steps process of capture and reconstruction of the light wavefront scattered from three-dimensional (3D) objects. Capture of the wavefront is possible due to encoding of both amplitude and phase in the hologram as a result of interference of the light beam coming from the object and mutually coherent reference beam. Three-dimensional imaging provided by holography motivates development of digital holographic imaging methods based on computer generation of holograms as a holographic display or a holographic printer. The holographic printing technique relies on combining digital 3D object representation and encoding of the holographic data with recording of analog white light viewable reflection holograms. The paper considers 3D contents generation for a holographic stereogram printer and a wavefront printer as a means of analogue recording of specific artifacts which are complicated objects with regards to conventional analog holography restrictions.

In medicine, optical polymers are used not only in ophthalmology but in many laser surgical, diagnostic and therapeutic systems. The application in lens design is determined by their refractive and dispersive properties in the considered spectral region. We have used different measuring techniques to obtain precise refractometric data in the visible and near-infrared spectral regions. Dispersive, thermal and other important optical characteristics of polymers have been studied. Design of a plastic achromatic objective, used in a surgical stereo-microscope at 1064 nm laser wavelength, is accomplished. Geometrical and wavefront aberrations are calculated. Another example of application of polymers is the designed all-mirror apochromatic micro-lens, intended for superluminescent diode fiber coupling in medical systems.