Том 26, № 3 (2018)

High-precision measurements of the spectral-line profile using near-IR diode lasers (DLs) have been performed, and the measurement results have been analyzed. To carry out these measurements, a multichannel DL spectrometer with a high spectral resolution was developed, calibrated, and put into operation. Particular attention has been paid to the deviation of the gases under study from ideal behavior. CO₂ of natural isotopic composition was chosen as a model gas.

A four level ladder scheme is employed for the realization of slow light large Kerr nonlinear indices in an asymmetric semiconductor three-coupled-quantum-well (TCQW) structure based on intersubband transitions. It is shown that a giant Kerr nonlinearity accompanied with negligible loss can be achieved by properly tuning the intensity of the control fields. A dressed state analysis is given to explain the origin of such a transparency based on slow light enhanced Kerr nonlinearity in this solid medium. In addition, we show that the three-photon detuning plays the important role in enhancing the third-order nonlinearity of the TCQW medium, and may provide new possibilities for technological applications in nonlinear optics and optical switching.

Expressions for the fields of crossed Gaussian beams with foci shifted relative to the point of intersection of their axes are derived. It is shown that the linear corrections in parameter ε=1/kρ₀ must be taken into account in the crossed-beam intensity distribution (in contrast to the case of a single beam). The interference of crossed Gaussian beams has been investigated based on the intensity calculations taking into account linear corrections to the Poynting vector. The residual electron energy in crossed pulses is multiply increased in comparison with the case of acceleration in a single Gaussian pulse.

We compared the heating and cooling theoretical and experimental transient times of DyPO₄ nanoparticles as a result of their heating by themultiphonon relaxation after femtosecond laser excitation in the near IR spectral range into different absorption spectral lines of the Dy³⁺ ion. We have shown that the relaxation of the heat flux to a stationary value occurs according to an exponential law. Depending on the value of the Biot number, two different relaxation mechanisms can be realized, in one of which the relaxation time depends on the thermal conductance of the interface, and in the other on the thermal diffusivity. It is shown that, after averaging over the ensemble of nanoparticles, the kinetics of the relaxation of the heat flux in these limiting cases has a substantially different character. The results might be helpful for assessing the prospects of the dielectric crystalline nanoparticles doped with rare-earth ions in the local hyperthermia treatment of cancer cells.

Room-temperature mid-IR emission from single-crystal silicon exposed to broadband (320 to 700 nm) light with power up to 150 m W has been revealed by Fourier transform IR emission spectroscopy. It is shown that broadband optical excitation significantly enhances IR emission in comparison with thermal emission. Spectral lines of lattice vibrations caused by interaction between combinations of longitudinal and transverse optical or acoustic phonons are identified in experimental IR emission spectra.

Experimental and theoretical study is given to the coupling of pulsed radiation in two adjacent end pump regions of the Nd:YAG solid-state active element in the passively Q-switched Cr:YAG laser. The two-channel laser generates a pair of short pulses with a fixed time delay of a few nanoseconds to 1 μs. The main factors affecting the delay time and spatial radiation profiles are experimentally found. A numerical model of pulsed lasing kinetics in this system is developed, and mechanisms for radiation coupling in the channels are determined. Power scaling in pulsed laser systems, synchronization of pulsed lasing in the submicrosecond duration range, generation of short intense pulse packets, and formation of the temporal envelope of a short laser pulse are discussed.

The forces acting on levitating water microdroplets in the structure of a droplet cluster (A.A. Fedorets, 2004) have been analyzed. It is found that microdroplets in the cluster should undergo low-frequency vertical damping oscillations near the equilibrium position. Oscillations occur also when switching on an external electric field, which affects the oscillation frequency and equilibrium position. Microdroplets are shown to lose their stability in the critical range of parameters. The electric fields are calculated in the simplest experimental scheme for simulating the effect of electric field on a droplet cluster.

The parametric interaction of ultrasonic and gravity-capillary waves (GCWs) on a liquid surface has been investigated. Harmonic modulation of the intensity of a plane ultrasonic wave incident on the liquid surface from the depth provides nonlinear parametric coupling of GCW wave triads. We determined the resonance conditions, providing spatiotemporal synchronism of interacting waves, and the threshold ultrasound intensities, at which an explosive-type instability develops in the system of standing and traveling GCWs.

In this paper, we introduce a linearized energy-preserving scheme which preserves the discrete global energy of solutions to the improved Korteweg−deVries equation. The method presented is based on the finite volume element method, by resorting to the variational derivative to transform the improved Korteweg−deVries equation into a new form, and then designing energy-preserving schemes for the transformed equation. The proposed scheme is much more efficient than the standard nonlinear scheme and has good stability. To illustrate its efficiency and conservative properties, we also compare it with other nonlinear schemes. Finally, we verify the efficiency and conservative properties through numerical simulations.