Nd3+ doped TeO2-ZnO glasses with double line waveguides produced by femtosecond (fs) laser writing technique are presented. The waveguides are written directly into these glasses using a femtosecond (fs) Ti:Sapphire laser, operating at 800 nm, delivering 30 fs pulses at 10 kHz repetition rate. Each written line is formed by several collinearly overlapping lines. When double line waveguides are produced, the light is guided in between the two lines and a negative refractive index change is produced in the region of the fs laser’s focus. However, as the absorption of the material at 800 nm (4 I9/2 → 4 F 5/2 + 2 H9/2 transition of Nd3+) is in resonance with the fs laser, the heating of the material makes writing difficult. In this context, the use of several overlapping lines represents a good alternative as the velocity of the writing can be increased to avoid, heating. We report results of output mode profile, beam quality factor M2 and refractive index change for, different parameters used for the fs laser writing. Pulse energies were 15μJ for 4 and 8 overlapping lines and 30 μJ for 2, 4 and 8 overlapping lines and the writing speed was 0.5 mm/s. The present investigation evaluates the best condition for the waveguides inscription, studying the influence of different parameters used in the writing process aiming at future photonic applications.
A new double line waveguide architecture produced in Nd3+ doped GeO2-PbO glasses is presented for photonic applications. These glasses produced with the melt quenching technique have interesting characteristics that make them attractive for photonic applications: large transmission window (400–5000 nm), large polarizability, low melting temperature (1200° C) with respect to silicates, low cut-off phonon energy (~800 cm-1 ), large mechanical resistance, high chemical durability and high refractive index (~2.0). The double line waveguides are written directly into Nd3+ doped GeO2-PbO glasses using a Ti:Sapphire femtosecond (fs) laser, operating at 800 nm, delivering 30 fs pulses at 10 kHz repetition rate. The two written lines that form the double waveguide are formed by several collinearly overlapping lines. Results of the output mode profile, the M2 beam quality factor at 632 and 1064 nm and refractive index change are presented, as well as the parameters used for laser writing. Double waveguides written with 4 and 8 overlapping lines, writing speed of 0.5 mm/s and pulse energy of 30 μJ demonstrated to be adequate parameters for writing; refractive index changes of ~10-3 were found at 632 nm for all the cases. The present results demonstrated that Nd3+ doped GeO2-PbO glasses with the new double line waveguide architecture are promising materials for the fabrication of passive and active components for photonic applications. Further investigation will focus on the influence of the writing parameters on the optical performance of the different waveguides, and evaluate the potential of the materials as optical amplifiers at 1064 nm.
We report the production of active double waveguides in germanate glasses, GeO2-PbO doped with Nd3+, by direct femtosecond laser writing. The glasses were produced using the melt-quenching technique and the active waveguides were written using 30 fs laser pulses at 800 nm with different parameters of writing speeds and pulse energies depending on the rare earth elements used for doping. The photo-induced refractive index change was 5.2x10-3. The Nd doped sample exhibited a relative gain of 3.6 dB/cm for 1.6 mW of 805 nm pump power. The results obtained in present work demonstrate that Nd3+ doped GeO2-PbO glasses are promising materials for the fabrication of integrated amplifiers, lossless components and lasers based on germanate glasses.
Dimensional characterization of microfluidic circuits were performed using three-dimensional models constructed from OCT images of such circuits. Were fabricated microchannels on the same BK7 glass plate, under different laser ablation conditions and substrate displacement velocity in relation to laser beam. Were used the following combination of energy, from 30 μJ to 60 μJ and velocity from 588 mm/min to 1176 mm/min, at 1 kHz laser repetition rate and 40 fs of pulse duration (FWHM). For OCT imaging we used an OCP930SR (Thorlabs System Inc) with 930 nm central wavelength, 6 μm of lateral and axial resolution, and image of 500 x 512 pixel corresponding to 2.0 mm x 1.6 mm of lateral and axial scans respectively at 8 frames per second. We also characterized devices like, micropumps, microvalves and microreactors. It was possible register the micropumps and valves in action in real time. Using the OCT images analyses was possible to select the best combination of laser pulse energy and substrate velocity. All the devices were made in raster protocol, where laser beam pass through the same path in a controlled number of times, and with each iteration more material is removed and deeper the channels remain. We found a deformation at the edge of fabricated structures, due to velocity reduction of substrate in relation to laser beam, which causes more laser pulses superposition in these regions, and more material is ablated. The technique was thus evaluated as a potential tool to aid in the inspection of microchannels.
The authors report the fabrication and characterization of passive waveguides in GeO2–PbO and TeO2–ZnO glasses written with a femtosecond laser delivering pulses with 3μJ, 30μJ and 80fs at 4kHz repetition rate. Permanent refractive index change at the focus of the laser beam was obtained and waveguides were formed by two closely spaced laser written lines, where the light guiding occurs between them. The refractive index change at 632 nm is around 10-4 . The value of the propagation losses was around 2.0 dB/cm. The output mode profiles indicate multimodal guiding behavior. Raman measurements show structural modification of the glassy network. The results show that these materials are potential candidates for passive waveguides applications as low-loss optical components.
Taking advantage of the inherent characteristics of femtosecond laser used for machining, we developed an interferometric system able to evaluate and correct the focal position with an accuracy of a few microns, implementing a technique based on low coherence interferometry. This approach measures at the exact spot that the laser is machining, in real time, and is sensitive to any sample that acts as a scatterer to the wavelength in use. The experimental evaluation was divided in two steps: in the first a system based on a superluminescent LED was mounted to check the viability and develop the controlling software; in the second part a setup was mounted employing a femtosecond laser, and several kinds of samples using the active focus control, among which the results obtained with glass sample and a bovine tooth are meticulously described in this paper. The system was able to improve the performance in both samples, keeping them in the confocal region for an extended positioning range, resulting in better engraving by the laser.
We report the use of the Diagonal Scan (D-Scan) technique to determine the ablation threshold of the AISI 1045 steel, a common engineering material that can be used as a probe for thermal effects, for superpositions ranging from single shot up to more than 10,000 pulses, for three pulses durations (25, 87 and 124 fs). It only took two hours of laboratory time to determine more than 20 ablation thresholds per pulse duration spanning 4 orders of magnitude of superpositions. The large amount of data generated shows a small deviation of the ablation threshold from the expected behavior, which can lead to the use of a model that better describes the dynamics of the ultrashort pulses ablation mechanism in metals.
Recently most analyses of Ca and P in different parts of tooth enamel have been performed semi-quantitatively. A direct and semi quantitative method for the determination of major and trace elements in human teeth by X-ray spectrometry is reported. The ratio Ca/P has been determined in the surface enamel of the third molar teeth. The surfaces were irradiated with short pulse laser Nd:YAG. The modifications in human dental enamel chemical composition for major and trace elements is here outlined. The accuracy of procedures was performed by analysis of natural hydroxyapatite as standard reference material. Results are consistent with other studies and they have indicated greater ratio Ca/P in irradiated groups in comparison to the non-irradiated group.
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