Bulletin of the Lebedev Physics Institute最新文献

We propose and experimentally demonstrate the possibility of efficient lasing at the C³Π_u–B³Π_g transition of the N₂ molecule in the afterglow of a high-pressure Ar–N₂–He mixture excited by an electron beam with an average electron energy ε_e ≈ 300 keV, an average current density j ≈ 30 A/cm², and a FWHM duration τ ≈ 100 ns. With a laser pulse duration of ∼110 ns, the laser energy is ∼65 mJ.

We report the results of numerical simulations of the generation of low-frequency Alfvén waves generated by periodic laser plasma bunches in a partially ionized background plasma. The effect of neutral particles on the structure, intensity, and velocity of the disturbances, as well as their maximum content in the plasma, are considered.

We consider a communication line without dispersion compensation. The pulse-broadening rate and the distance at which stationary signal power statistics are established are estimated. It is shown that the probability of exceeding a given power level decreases exponentially with increasing level.

For the boson sampling problem, a validation method is proposed based on the analysis of the space of measured Fock states expressed as strings of non-negative integers. The method is based on introducing a radial function ({{G}_{{{{p}_{0}}}}})(r) in the space of such strings with an l₁-metric. The function ({{G}_{{{{p}_{0}}}}})(r) depends on the internal structure of the collected statistics for strings of integers and will therefore differ significantly for different samplers. The method is tested for samplers with Fock, coherent, and thermal states, as well as for distinguishable particles in the nonunit quantum efficiency regime of the measuring photodetectors. It is shown that for a photon loss probability p_loss ≤ 0.1 at the photodetector, the radial function of a sampler with Fock states is qualitatively different from that of samplers with coherent and thermal states. Knowledge of ({{G}_{{{{p}_{0}}}}})(r) in this case is sufficient to qualitatively distinguish a boson sampler from those described above. For p_loss ≥ 0.2, the radial functions of the Fock, thermal, and coherent samplers may be superficially similar. Validation in this case is only possible if, in addition to the radial function, the p_loss value is known. A statistical test is used for validation. The radial functions ({{G}_{{{{p}_{0}}}}})(r) of a Fock sampler and a sampler with distinguishable particles are qualitatively indistinguishable for any p_loss loss level. Therefore, p_loss must be known to statistically distinguish these samplers.

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.