Bulletin of the Lebedev Physics Institute最新文献

The possibility of amplifying a single-frequency signal at a wavelength of 1367 nm in bismuth-doped optical fibers with single-mode (laser using the nonlinear optical effect of stimulated Raman scattering, Raman laser) and multi-mode (laser diodes) pumping has been investigated. The use of a Raman fiber laser with a radiation wavelength of 1205 nm and a power of ~2 W, and bidirectional pumping injected into the core of a single-mode bismuth-doped optical fiber increased the signal power from 11 to 342 mW (gain of ~15 dB). An output signal power of 155 mW (gain of ~11.5 dB) was achieved using multimode laser diodes with a wavelength of 793 nm injected into the cladding of an active single-mode optical fiber. In both cases, the spectrum of the single-frequency signal was not distorted after amplification when measured using a spectrum analyzer with a hardware function of 20 pm, while the relative intensity noise (RIN) of the amplifiers did not exceed –140 dB/Hz.

Two compact fiber lasers generating in the range of 1535 nm, which are based on a specially developed composite highly doped erbium fiber, are presented. A DFB laser based on a 4.1-mm-long phase-shifted fiber Bragg grating (FBG) generates single-frequency radiation with single polarization; the linewidth is ~3 kHz and the output power is 170 µW at a pump power of 450 mW. The laser with a linear cavity configuration formed by the FBG and a dielectric mirror, which has a length of the active medium of 1.3 cm, also demonstrates single-frequency radiation with a linewidth of ~1 kHz and an output power of 1.08 mW at a pump power of 400 mW. As far as we know, these lasers have record-breaking short cavity lengths in their classes with the spectral and power characteristics suitable for a wide range of applications.

A grazing-incidence reflective zone plate is designed for operation at a wavelength of 135 Å in the first diffraction order, at a wavelength of 67.5 Å in the second order, and so on. A spectrometer with a reflective zone plate with a flat field in the 125–235 Å rang is proposed. Using numerical ray tracing, the spectral image of a point source is calculated at wavelengths of 135 and 135.1 Å, as well as 125, 125.1, 130, 130.1, 140, 140.1, and 145, 145.1 Å. It is shown that the spectral resolution in the flat field region exceeds 10³, and the spatial resolution in the crossed direction at the selected wavelength of 135 Å is no worse than 1 μm. The reflective zone plate is an effective tool for diagnosing the spatial and spectral parameters of a laser-plasma soft X-ray source.

This study investigates the impact of light coherence on the photoinduced response of the bacteria Pseudomonas fluorescens. A cell suspension was exposed to brief periods of irradiation in the excitation region of the direct or reverse phyB photoconversion. Quasi-monochromatic radiation fluxes with equal intensity but different spatial and temporal coherence were formed in each spectral range. The effect of light exposure was judged by the number of cells in the fixed (0.06 mm²) field of view during microscopy of the suspension preparations. Photon correlation is shown to affect the photoinduced response of bacteria in both direct and reverse phyB photoconversion. The discovered effect can be used for selective control of the functional activity of prokaryotic cells.

To form ring inversion profiles in a Rhodamine 6G dye laser (λ_las ≈ 580 nm), a cuvette with an axicon was used in the 532 nm dye pumping channel. The axicon worked both in air and in the cuvette filled with liquid. By using different liquids, we can control the size of the inversion ring in the dye, exciting Laguerre-Gaussian modes (LG_0l) of lower and higher orders. Non-planar geometric modes are obtained in degenerate configurations of a plano-spherical resonator. They form various discrete structures of lasing spots localized on the rings. The process of switching the lasing regime from the ring geometric mode to the LG_0l mode is demonstrated when the cuvette with the axicon is filled with liquid. Experiments have shown that dye lasers are convenient objects for testing various methods of exciting structured laser beams.

The output power of a fiber-optic temperature sensor based on a Michelson interferometer integrated into an inner-clad optical fiber is increased by approximately 14 dB by depositing a gold mirror approximately 100 nm thick on the fiber end face. Studies of the long-term temperature stability of the sensor demonstrate that the gold coating markedly degrades during annealing at temperatures of 450°C and above.

We report an analysis of the dependence of the number and energy of electrons ejected and accelerated by a laser pulse from a submicron-sized cluster on the incident radiation intensity and the cluster size. It is shown that the temperature of the “hot” part of the spectrum of electrons accelerated from such clusters is almost independent of their size and increases proportionally to the laser radiation intensity.

We report an investigation of the X-ray spectra of a high-temperature, dense aluminum plasma produced by laser heating and in a high-current pinch. The spectra are measured using the same spectrograph, which helps avoid difficulties in their interpretation and comparison. This approach is shown to be critical when the recording parameters cannot be specified with high accuracy. The spectra are simulated, and plasma parameters are determined. Spectral features associated with differences in the plasma generation methods are identified.

Based on the Huygens–Fresnel principle, we present a vector description of laser beam propagation without the limitations of the paraxial approximation. A numerical model is developed for a family of radially (azimuthally) polarized beams with circular symmetry of all parameters, including polarization. The model takes into account the transverse nature of the electromagnetic wave as it propagates from points of a given cross section to observation points. Diffraction from a narrow annular slit and the evolution of beams with damaged amplitude–phase field distributions are considered. On the basis of numerical calculations, a method for extracting high-quality radiation from lasers with a coaxial active medium geometry is proposed.

The effect of SARS-CoV-2 inactivation has been established in the wavelength range of 343 to 401 nm. The results of determining the spectral sensitivity and threshold cycle for RNA fragments of SARS-CoV-2, when exposed to radiation in the human-safe UVA range, are presented. The findings can be used to create human-safe sources of virus eradication in public places.