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Nanostructure Formation of the Solid Surface under the Action of Intense Laser Radiation
Full text linkThe paper describes the mechanism for formationof periodic nanostructures on the surface of solidsunder the action of intense laser radiation. Themodel based on a nonlinear relaxation oftemperature-induced stresses. The solid deformedby laser radiation is considered in a form of threesimultaneously coexisting phases. The system ofequations, which describes these phases, is reducedto the generalized Ginzburg–Landau equation thathas a periodic solution. For estimation thecalculation of the step of the periodic structurearising on the silicon surface under the action of alaser pulse is done
Application of laser texturing method for mc-Si solar cells fabrication
Full text linkThe results of the experiments on the “black” mc-Si surface fabrication by the nanosecond pulses of the YAG laser second harmonic and on application of the introduced laser texturing method for the mc-Si solar cells efficiency improvement are represented. The developed version of laser texturing permits producing a low-reflection mc-Si surface with the reflectance of ~3% in the spectral range of 0.3-1.1 μm. The application of the introduced laser texturing method in mc-Si solar cells fabrication makes it possible to increase the short circuit current density and quantum efficiency
Generation and propagation of polarization singularities in second harmonic generation from the surface of the isotropic gyrotropic medium
Full text linkWhen proceeding to the oblique incidence from thenormal incidence geometry in surface secondharmonic generation, the symmetry of the problemand, thus, of the reflected signal beam breaks. Inthis case there can appear C-points in thetransversal section of the signal beam. Using theanalytical formulae obtained in previous works, westudied the conditions of appearance and thebehaviour of the C-points in reflected signal beam(in particular case of SHG), and also the way of theline-to-point singularity transformation
Efficient femtosecond optical parametric amplification and wavelength conversion in silicon waveguides
Full text linkEfficient femtosecond optical parametric amplification and wavelength conversion via four-wave mixing (FWM) in silicon waveguides are demonstrated. In the femtosecond FWM process, the spectra are greatly broadened, and it is difficult to achieve efficient wavelength conversion and parametric amplification when the pump and signal pulse widths are close to or less than 100 fs because of the spectral overlap. The spectral overlap can be suppressed by tailoring the dispersion profiles of the silicon waveguides, and separable spectra are obtained for parametric amplification with 200 fs pulses. On-chip parametric gain as high as 26.8 dB and idler conversion gain of 25.6 dB is achieved with a low pump peak power over a flat bandwidth of 400 nm in a 10-mm-long dispersion engineered silicon waveguide. In addition, the impact of initial chirp on the wavelength conversion is also investigated, and relative narrower FWM spectra with most of the energy remain in the central peak can be obtained using appropriate initial chirp. The conversion bandwidth greater than 500 nm with peak conversion efficiency of -1.6 dB can be obtained
Photoacoustic section imaging with integrating detectors
Full text linkPhotoacoustic section imaging is a method for visualizing structures with optical contrast in selected layers of an extended object. In order to avoid resolution limitations that are due to commonly used ultrasound detectors of finite size, we propose the use of extended, integrating cylindrical elements for focusing the acoustic detection into the selected section. Two imaging methods based on piezoelectric and optical detection are presented. Resolution limits and results on zebra fish are demonstrated
Explosive Boiling of Transparent Liquids on Absorbing Targets Heated by Short Laser Pulses
Full text linkExplosive boiling induced by sub-nanosecond laser pulses is theoretically analyzed in the case of transparent liquids on metal targets. In this case the variation of boiling start times due to inhomogeneous distribution of laser intensity through the irradiation spot can be reduced up to laser pulse duration and registered explosive boiling pressure signals become less distorted. The results are compared with experimental investigations of photoacoustic (PA) signals induced in metal target under transparent liquid layer irradiated by laser pulses of about 100 ps duration and wavelength 532 nm
Photon Synthesis of Nanometric Films Based on Transitional Metal oxides for Multi-Parameter Sensors
Full text linkThe reactive pulsed laser deposition (RPLD) based on a KrF laser was used for photon synthesis of nanometric iron and chromium oxides films. RPLD allows controlling the thickness and stoichiometry of deposits with definite band gap. So RPLD was used for synthesizing nanometric iron and chromium oxides films for thermo-photo-chemical sensors. We compared sensing properties of iron and chromium oxides nanometric films deposited on <100>Si substrate by RPLD. These iron and chromium oxides films have semiconductor properties with the band gaps less than 1.0 eV. The largest photosensitivity of iron and chromium oxides films was about 44 Vc/W and 2.5 Vc/W, accordingly, for white light at power density ~ 6x10-3 W/cm2. Vc is “chemical” photo e.m.f.. Maximum value of thermo electromotive force (e.m.f.) coefficient of iron and chromium oxides films was about 1.65 mV/K and 3.5-4.5mV/K, accordingly. Iron oxides films were tested as chemical sensors: the largest sensitivity of NO molecules was at the level of 7x1012 cm-3. Our results showed that nanometric iron and chromium oxides films synthesized by UV photons can be used as up-to-date materials for multi-parameter sensors operating at moderate temperature
Pulse Laser Deposition method for UV-Photocathode production
Full text linkProduction method of alkali halides UVphotocathodes durable to environment exposure was proposed. Photocathodes with highhomogeneous and adhesion photoemission layerwere made. Quantum yield measurements results ofmanufactured photocathodes are presented.Developed method is promising for creation of highaperture electron injectors and detectors
Zero-distance pulse fronts of stretcher and its optical system
Full text linkA two-grating stretcher is a dispersion delay line that is widely used in chirped pulse amplification for ultrafast laser pulses. If the stretcher consists of two reflecting diffraction gratings with a perfectly reflective optical system between them, its dispersion can be calculated by using the concept of a „„zero-distance pulse front.” We introduce the concept of a „„zero-distance pulse front” of the real optical system, which characterizes its aberrations. The similarity of these zero-distance pulse fronts allows us to study the influence of aberrations in an optical system on the dispersion of a stretcher
Broadband Superfluorescent Source Based on Bismuth-Doped GeO2-SiO2 Fiber
Full text linkThe first bismuth-doped superfluorescent fibersource operating at 1.44-μm was developed. Atpump power of 200 mW and pump wavelength of1310 nm, its output signal reaches 57 mW withspectrum width of 25 nm
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