Bulletin of the Lebedev Physics Institute最新文献

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.

A method is proposed and implemented to determine a set of constants for collisional processes that ensure an energy exchange between 2p states of the laser cycle in an optically pumped argon metastable laser. The time dependences of the spontaneous emission of these states after selective excitation with narrow-band pulsed radiation from a tunable laser are observed experimentally and compared with the results of simulation. Additionally, conditions obtained using integral relations for the populations of the observed excited states of the argon atom are imposed. The results indicate a pathway for the transfer of optical pump energy to the upper laser level that differs from previous concepts.

The paper examines the key features of the laser sintering method for compressed ceramic-polymer powder materials, enabling the fabrication of composite films with a high filler content and significant open porosity. The laser parameter limits for the formation of composite films for ceramic-polymer composites with different ceramic fractional compositions are determined. It is shown that at a wavelength of 10.6 μm, films with a thickness of 50 to 150 μm can be produced; a wavelength of 1.06 μm allows only thick layers of several hundred micrometers to be formed. During sintering with radiation at a wavelength of 1.06 μm, extrusion of a portion of the ceramic filler onto the pore surface is observed, while at a wavelength of 10.6 μm, this effect is almost absent. The processes of thermal-oxidative degradation of polyvinylidene fluoride under the action of laser radiation are studied. It is found that under nonequilibrium heating conditions, intermolecular and intramolecular dehydrofluorination processes and the decomposition of molecular chains occur simultaneously; the presence of a ceramic filler intensifies these processes.

We report a theoretical study of the effect of donor doping of a CdS/ZnSe/ZnSSe quantum-well heterostructure on optical gain and luminescence spectra. It is shown that doping leads to a decrease in the threshold pump level at which optical gain arises, and reduces the short-wavelength shift of the luminescence line with increasing pump level, which is inherent in heterostructures with type-II band offsets.

The results of investigating N₂ lasers pumped by a pulsed longitudinal discharge are presented. Conditions have been defined for stable burning of a volume discharge of 40 ns duration at a current density up to 5 kA/cm² and a specific pump power up to 10 MW/cm³. A generation energy of 3.5 mJ and a pulse full width at half maximum up to 24 ns are obtained. The temporal and spatial behavior of laser radiation is investigated. The ability of the laser to operate in pulse-periodic mode with a pulse repetition rate up to 100 Hz is shown.