The spectral beam combining for narrowband laser beams with spectral width below 1 nm by using of Transmitting Bragg Gratings (TBGs) has already shown high efficiency and high quality of a combined beam. For high power lasers emitting broadband beams with spectral width exceeding 1 nm, it is necessary to consider effect of TBGs spectral dispersion on divergence of a combined beam. In this work, the interaction of polychromatic radiation with TBGs was simulated by the Floquet approach. The scheme for spectral dispersion compensation of broadband beam is described.
Laser material processing applications often require the flat-top beam profile within focal spots ranged below 100 μm. For high power applications, volume phase masks recorded in photo- thermo-refractive glass (PTR) are promising. The problem is how to achieve simultaneously a high-quality shape and a small size of the beam. The commercial phase masks usually show large power losses in the beam wings, only about 40% of the energy was concentrated under the 95% level. By applying a gray phase mask instead of binary mask, one can reduce losses in the wings of the beam. In this work, a spatial light modulator (SLM) with designed computer generated holograms (CGHs) was used as a beam converter. Using the SLM with programmed gray mask allows obtaining flexible laser beam shaping, but beam quality is limited by imposed parameters of the SLM. The requirements for obtaining a square flat-top beam with energy lost in wings less than 10% is described. It was found that for sharp edges of the square flat-top beam, it is necessary that the size of the output beam contains at least 16 pixels of SLM. This fact is a consequence of the Fourier transform, where high spatial frequencies are responsible for the shape. The concept design of the scanning progressive mechanism of the master volume phase mask recording to exclude the influence of SLM work area dimensions is discussed.
In the work borate glasses with additives of copper and fluorine is considered. The luminescence quantum efficiency of these glasses reaches 50 % in the visible range. Therefore the concerned borate glass is the promising material for solar cell down-convertors, sensitive elements of the spark sensors and UV detectors and as a cheap phosphor for warm-white LEDs. All that makes boron glass doped with copper ions promising for use in devices such as spark sensors, down-converters, cheap phosphors for white leds.
Electrical as well as photoelectrical properties of the metal nanoparticle ensembles (MNEs) were investigated. The
exponential temperature dependence of the conductivity in the MNEs was obtained. Since lnIc depends linear on 1/T, an
activation energy concept of the conductivity can be applied. An activation energy of Eact = 0.50 eV for Ag nanoparticles
has been extracted. The photoconductivity of MNEs has been related to their extinction spectra. A clear evidence of the
photoinduced conductivity of the MNEs was obtained. Considerable enhancement of the photocurrent was observed for
those wavelengths that are in resonance with plasmon excitations localized in the metal nanoparticles forming the MNE.
The increased photoconductivity can be explained by the additional energy placed in the nanoparticles due to the
excitation of an LSPPR.
In the present work the mechanisms of the optical radiation action on the Na metal island films, representing ensemble of
nanoparticles deposited on a dielectric substrate and interacting with each other due to the electron transport between the
islands, were investigated. The major effect of optical radiation action on the film conductivity was found to be caused
by photons with the energies above the threshold of the photoeffect in Na. The appreciable action of illumination with
the wavelengths greater than the photoelectric threshold was also detected and interpreted.
The shape of the luminescence spectrum of Cs atoms flying near a sapphire surface is explored experimentally and described phenomenologically for the detuning range of 5 to 50 cm-1 on both sides of D2 line. The numerical fitting of one theoretical parameter and a small variation of another parameter ensure a satisfactory agreement with the experimental spectrum. The experimentally determined abnormally high intensity of the antistatic wing is explained by the effect of phase relaxation of the atomic transition, caused by fluctuations of the electric field of oscillating ions of the sapphire crystal lattice.
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