Bulletin of the Lebedev Physics Institute最新文献

A comparative analysis has been made of the superluminescence spectra of two HPHT diamond samples with NV¯-centers with the concentration in the growth sectors {111} of NV¯-centers ≈10 ppm and of C-centers ≈ 45 ppm. A broad structureless superluminescence band with a maximum about 706 nm and a narrow band in the region of 705 to 720 nm were identified in the spectral range of 650–750 nm when excited by pulsed laser radiation at λ = 532 nm. It was found that the narrow-band superluminescence was not excited by pumping with continuous radiation at λ = 532 nm and the intensities of both types of superluminescence were summated under simultaneous pumping by continuous and pulsed radiation at λ = 532 nm. These data indicate either the different nature of the two types of superluminescence or that they belonged to NV¯ centers but with different excitation mechanisms. The existence of connection between the shape of the spectra of narrow-band superluminescence and of radiation pulses has been demonstrated. The observed features of narrow-band superluminescence are explained for the first time by the occurrence of mode-locking laser generation. The mode-locking laser generation without the use of reflective coatings on the sample or an external resonator on other laser materials has not been observed before.

We consider single-beam 3D imaging, i.e., an approach to reconstructing the complex dielectric constant ε(x, y, z) of a sample in question by processing data read from a detector during successive illumination of a stationary object with different Gaussian beams along the same direction (angle). The propagation of Gaussian beams through an object is described using the parabolic wave equation. The equation for single-beam volume imaging is derived, which relates the data obtained on the detector with the values of the dielectric constants ε(x, y, z). As an example of solving this equation using optimization methods, a simplified case of purely real dielectric constant ε(x, z) in two-dimensional space is considered.

Optically pumped metastable rare gas lasers (OPRGL) have been investigated. Lasing based on metastable neon (Ne*) atoms in a Ne–He mixture in a pulsed regime with transverse optical pumping was produced for the first time. Ne* was produced in the plasma of a nanosecond repetitively pulsed glow discharge with a frequency of 200 kHz. Pulsed optical pumping was provided by a dye laser at wavelengths corresponding to neon transitions of 1s₅ → 2p₉ (640.2 nm) and 1s₅ → 2p₈ (633.4 nm). The effect of various gain medium parameters on lasing characteristics was experimentally determined. Ne*–He OPRGL generation thresholds were measured by optical pump intensity of 1s₅ → 2p₉ and 1s₅ → 2p₈ transitions.

Optimization of laser synthesis regimes producing colloidal solutions of boron nanoparticles for their application as a promising boron-containing agent of boron neutron capture therapy (BNCT) of oncological diseases is an up to date trend in BNCT advancement. In this study, colloidal solutions of boron nanoparticles (BNPs) were synthesized by laser fragmentation in organic solvents using laser pulses of nanosecond and femtosecond duration range. The powder of the stable ¹⁰B isotope of submicron fractions with arbitrary surface morphology served as starting material in both cases. The dependence of the properties of produced nanomaterials on the duration of laser pulses was compared directly.

We report the construction of an analytical model that allows one to calculate the emission intensity of laser plasma which is generated by heating cluster targets with relativistic laser pulses. The results of particle-in-cell (PIC) calculation of plasma density and temperature obtained using the EPOCH software package are used as input parameters of the model. The constructed model is used to calculate the interaction of femtosecond laser pulses with an intensity of up to 10²² W/cm² with large (0.5–2 μm) argon clusters. The emission duration and the total number of photons emitted in the resonance lines of He- and H-like argon ions are analyzed. It is shown how this model in combination with PIC calculation can be used to optimize the parameters of ultrafast X-ray sources.

Investigation of spontaneous and stimulated Raman scattering in a crystal of sodium dimolybdate, Na₂Mo₂O₇ with an orthorhombic structure is presented. Polarized Raman spectra corresponding to six independent components of the Raman tensor have been obtained. The phonon frequencies were determined and the oscillations were identified by types of symmetry. Raman-laser mode in Na₂Mo₂O₇ has the highest frequency value among the molybdate crystals, equal to 939 cm^–1. For the first time, Raman oscillation was obtained on a Na₂Mo₂O₇ crystal when excited by pulses of Nd:YLF laser with a wavelength of 1047 nm and a duration of 25 ps. The Raman gain coefficient at optimal orientation was 12.4 cm/GW, which is one of the highest values for solid-state Raman media. The described studies have shown that the sodium dimolybdate crystal is a promising nonlinear medium for creating a solid-state Raman converter.

Based on analytical estimates and numerical simulation, we consider the generation of a superstrong magnetic field by a circularly polarized laser pulse in a laser target shaped as a hollow cylinder with a radius of a fraction of a micrometer. The amplitude and lifetime of the magnetic field in this target is shown to additionally increase due to the compression of the cylinder.

The efficiency of AgGaS₂, BaGa₄Se₇, and HgGa₂S₄ crystals has been investigated in a mid-IR frequency difference generator based on a femtosecond ytterbium fiber laser with a wavelength of 1.03 μm, pulse duration of 0.25 ps, pulse repetition rate of 10 kHz, and average radiation power of 5 W. It is shown that under the given experimental conditions the highest efficiency of difference-frequency generation (up to ~7.5%) is achieved with a HgGa₂S₄ crystal that provides 2 or 3 times higher energy of pulses with a wavelength of 4 to 7 μm (up to 6 μJ) without damaging it. In addition, this crystal yielded the longest wavelength of converted radiation—11 μm with pulse energy ~1 µJ.

We report a study of optical properties of silver and gold nanoshells with a semiconductor core and an external organic layer of the molecular J-aggregate of the TDBC dye. Absorption and scattering cross sections of light are calculated using the generalized Mie theory for three values of the outer radius of the intermediate metal shell of the nanoparticle (10, 70, and 100 nm), with its thickness varying in the range from 0 to 20 nm. Qualitatively different behavior of the optical spectra of the studied nanostructures is demonstrated depending on their composition and geometric parameters. It is found that for the considered core materials (Si, GaP, and ZnSe) in the system in question, weak and strong plasmon–exciton coupling regimes can be implemented, including regimes exhibiting the induced transparency effect. It is shown that in the light scattering cross sections of three-layer ZnSe/Au/TDBC nanoparticles, the Fano antiresonance effect is observed, manifested in the asymmetric behavior of the spectral band contour. The above effects stem from the near-field electromagnetic coupling of dipole and multipole plasmons in the intermediate metal shell (Ag or Au) of the system with a semiconductor core and an outer organic excitonic shell. The results of the work contribute to a deeper understanding of the effects of near-field electromagnetic coupling in metal-containing organic–inorganic nanostructures. The studied nanoparticles are of interest for the development of new hybrid materials with specified optical properties and for the creation of a number of effective photonic devices on their basis, including highly sensitive sensors and photodetectors.

Core–shell samples of thin films of tantalum nanoclusters and of tantalum oxides on silicon were obtained. The chemical composition of Ta/TaO₂ nanoclusters was determined based on the results of X-ray photoelectron spectroscopic (XPS) analysis. The homogeneity of the thin nanocluster film composition was ascertained by the character of angular dependences of the ratios of the Ta4f doublet and oxygen peaks. The effect of a dimensional shift of binding energy was observed for metal tantalum nanoclusters with the diameter d < 5 nm, and its dependence on the nanocluster diameter was established.