Bulletin of the Lebedev Physics Institute最新文献

A laser on a CdSSe single crystal with a wavelength of 623.5 nm with longitudinal two-photon pumping by radiation from a Q-switched Nd : YAP laser has been studied. When the single crystal was cooled to liquid nitrogen temperature, a peak power of up to 80 kW was achieved with a pulse duration of 7 ns and an efficiency of ~3%. The full divergence angle of the laser depended on the pump spot diameter and was approximately 30° at a 1-mm diameter. The power was limited by the crystal-surface destruction. Ways to improve the laser performance are discussed.

We report the method of modulation piezoelectric resonance laser calorimetry (MPLC) for studying the interaction of nonlinear optical crystals with laser radiation. The kinetics of the crystal heating power is measured during laser radiation propagation, and the method is based based on periodic irradiation of the sample and the isolation of the amplitude of its equivalent temperature oscillations. The theoretical justification for the MPLC technique and its approbation was performed by studying LBO crystal degradation under UV irradiation.

We report a comprehensive study of the spatiotemporal dynamics of miniature, broad-area, vertical-cavity surface-emitting lasers (VCSELs). The main attention is paid to the development of methods for stabilizing their output using external optical injection. A detailed analysis demonstrates that free-running VCSELs exhibit chaotic dynamics caused by modulation instability. This leads to beam filamentation and a significant deterioration in its spatiotemporal characteristics. An improved mathematical model is considered that takes into account key features of semiconductor active media, including the Henry factor, which allows the observed nonlinear effects to be adequately described. It is found that external optical control not only effectively suppresses the development of instabilities but also ensures the formation of controllable spatial structures. In particular, the possibility of generating regular patterns (stripe, ring, and hexagonal structures) and controlled switching between them is demonstrated. The obtained results are important for the development of stable compact laser systems for applications in photonics, optical information processing, and communication systems, where precise control of the spatial characteristics of radiation is needed.

A kinetic model has been developed for the optical cooling of the rotational levels of the CaO⁺ (X²Π, ({v}) = 0) molecular ion ground state. This was achieved by placing the molecular ion in an ion trap and subjecting it to laser and thermal radiation. The model includes (1) excitation of the electron level (B²Π, ({v}) = 8) by tunable broadband laser radiation with a frequency cutoff option and overlapping the bandwidth of spectral transition, (B²Π, ({v}{{'' }}) = 8) ← (X²Π, ({v}) = 0), with the ground state rotational quantum number values, J > J_m; (2) interaction with the thermal radiation from the medium; and (3) spontaneous radiative relaxation of excited states. The laser cutoff frequency coincided with the frequency of transition from the state of (X²Π, ({v}) = 0, J = J_m. The simulation includes 50 rotational levels for three electron states of X²Π, A²Σ⁺, and B²Π, 42 vibrational levels for X²Π and A²Σ⁺, and 9 vibrational levels for B²Π. The levels of the lower electron excited state were dispersed by inducing the radiation of the second laser at the transition (A²Σ⁺, ({v}{{'}}) = 1) → (В²Π, ({v}{{'' }}) = 8). The rates of radiation transitions between states were determined based on calculated values of Einstein coefficients and flux densities of laser and thermal radiation. It is shown that the rotational level populations are depleted by laser radiation in tens of milliseconds, simultaneously with a significant accumulation of the population of “dark” levels with J < J_m. At a spectral cutoff of 33256 cm^–1 (J_m = 0.5), the population of the X²Π state (({v}) = 0, J = 3.5) is eight times higher than the thermal state (T = 300 K).

The paper examines the generation of an ultrashort pulse in a laser plasma and its amplification using a free-electron laser undulator during interaction with a relativistic electron bunch, including that produced by a petawatt laser. The goal of this study is to determine the system parameters that enable the generation and significant amplification of ultrashort pulses, with durations down to an attosecond.

Results are presented of research in building a noncontact accelerator of cryogenic fuel targets (CFT) using HTSC MAGLEV technology proposed by the Lebedev Physical Institute (LPI) of the Russian Academy of Sciences. The goal of the ongoing research is the injection delivery of CFT using a levitating HTSC sabot into the target chamber for interaction with laser radiation at setups of medium and megajoule level. In the context of the future inertial confinement fusion (ICF) reactor, we need to speed the CFT up to high injection velocities (200 to 400 m/s for a target chamber radius of ~6 m) to prevent damage to its components (particularly the cryogenic layer) by thermal emission from hot inner walls of the target chamber (T_ch ~ 1758 K). In addition, the CFT should be suspension-free for spherically-symmetric laser irradiation. It is a fundamental condition for the CFT injection delivery at the thermonuclear burn zone with the required frequency of 5 to 10 Hz and for maintaining the quality of the cryogenic fuel layer up to the CFT irradiation. We have carried out theoretical and experimental modeling of the CFT injection conditions for operating ICF facilities. The injection velocity, ({{{v}}_{{{text{inj}}}}}), required to prevent thermal damage to the CFT is shown to be 3.2 to 17 m/s for the target chamber wall temperature T_ch = 300 K and the chamber radius ranging from 1 to 5 m. To achieve these parameters, a levitation-based CFT accelerator is being developed by the LPI in order to avoid target heating already at the acceleration stage due to mechanical friction because the permissible temperature deviations in the CFT should not exceed 100 mK. Based on the results, the plan is to conduct the first experiments with noncontact acceleration of a HTSC sabot with CFT, its subsequent deceleration and CFT injection at the laser focus using the GARPUN laser facility operating at the LPI.

We report a theoretical study of the spatiotemporal dynamics of wide-aperture lasers with a homogeneous line broadening using the Maxwell–Bloch model. Three dynamic classes of lasers (A, B, and C) are considered, for which a linear stability analysis of homogeneous steady-state generation is performed. It is shown that in class A and B lasers, the development of wave instabilities leads to the formation of complex transverse optical structures, whereas class C lasers are characterized by a homogeneous Hopf instability, accompanied by spatially homogeneous intensity oscillations. The secondary instabilities arising in class C lasers are studied using the Floquet method, and the parameters at which nonlinear optical structures, including spiral wave domains, are formed are determined. Numerical simulations confirm theoretical predictions and demonstrate the feasibility of suppressing secondary instabilities using external optical injection.

Experiments and numerical simulation demonstrate the feasibility of forming convective currents to capture and transfer 2.9 μm polystyrene microspheres in a cuvette cooled down to 5°C. The velocity of the currents is shown to depend on the gradient of temperature regardless of its initial level. Furthermore, the temperature in the manipulation region can drop to between 25 and 35°C. These results were obtained for point and ring optothermal traps.

Using in situ laser surface probing, we study the interaction of broadband high-power radiation from a pulsed high-current discharge in background gas media (Ar and air) with the surface of a model dielectric mirror (ZrO₂/SiO₂). Sources based on pulsed high-current (I > 100 kA) plasma dynamic discharges generate high-brightness radiation fluxes, including those in the vacuum ultraviolet (VUV) spectrum. Changing the composition of the background gas enables radiative spectrum tuning, by controlling the short-wavelength emission limit. Characteristic values of the integrated (over the entire spectrum) radiant energy flux density at a distance of 78.6 cm from the source axis under the implemented conditions range from ∼14–25 kW/cm² (discharges in air) to ∼37–112 kW/cm² (discharges in argon). The obtained results indicate the occurrence of several gas-dynamic processes (evaporation, plasma layer formation, etc.) near the irradiated mirror, whose intensity reaches a maximum within 12–15 μs, which is confirmed by shielding the scanning laser beam. It is shown that the characteristic time of plasma flow emission above the surface is ∼30–40 μs.

The paper presents the findings of a numerical and experimental study on the relationship between the scattered light intensity and scattering angle for water droplets in an immiscible liquid and of polystyrene microspheres in water. The study investigates the nature of nonmonotonic dependence of intensity on the amount of scattering impurity at certain specific angles. The work is a part of a project to develop an optical sensor for monitoring water content in jet fuel.