Sergei A. Akhmanov

Thermal self-actions of laser beams

Theoretical and experimental studies of thermal self-defocusing and self-focusing CW laser beams in liquids and solids are given. An analytical theory of thermal self-actions, including aberration phenomena, is developed. Special attention is given to the problem of thermal self-defocusing in liquids with flows (wind or convection). The new effect of continuous light-beam deflection in absorbing moving media is discussed.

Parametric interactions in optics and tunable light oscillators

The paper presents the review of the latest works at the University of Moscow in the field of pulsed parametric oscillators and the new application of parametric light interaction-nonlinear spectrograph. This spectrograph is based on the steep frequency dependence of phase-matched angles for nonlinear mixing processes. Two new types of oscillators are considered: one having a cavity without dielectric coatings, the other a travelling-wave oscillator that is really an amplifier of parametric superluminescence. The latter has a narrow spectrum of radiation (1-2 A). The most possible applications of oscillators and their necessary characteristics are given.

Development of Cars for Measurement of Molecular Parameters

A new modification of Coherent Active Raman Spectroscopy (CARS) technique which gives a possibility of coherent subtraction of a nonresonant term in the nonlinear susceptibility is proposed and experimentally investigated. The CARS method with a broadband pump is discussed for the purpose of instantaneous analysis of rarefied gases and samples with low vapor pressure. CW CARS was used to study liquids. It was shown that CARS using single-frequency cw tunable lasers is an excellent method for ultrahigh resolution Raman spectroscopy. CARS with tunable lasers [1,2] has recently been extensively applied both to measurements of nonlinear susceptibilities [3,4,5] and for analytic purposes, particularly for analyzing gas mixtures [6,7,8] . Attention will be paid here to the new aspects of CARS for measurements of molecular parameters.

Soft x-ray production and harmonic generation in femtosecond laser-driven plasma

The picosecond soh X-ray source based on femtosecond laser-driven plasma and spherical multilayred mirrors is developed. Results on VUV laser plasma spectrum. investigation and second harmonic generation are reported.

Infrared coherent lidar systems for wind velocity measurements

Doppler lidars are prospective means for long-range measurements of wind velocity in the atmosphere, based on the registration of Doppler frequency shifts in the radiation backscattered by moving aerosol particles. The development of coherent lidar systems based on CW and TEA CO2 and on Nd:YAG lasers is presented. Test results from the application of these lidars to atmospheric wind velocity measurements are discussed.

CARS thermometry of polyatomic gases: SF 6

Coherent anti-Stokes Raman spectroscopy (CARS) has been used to study the temperature behavior of SF 6 gas. In the temperature range 200-1000 K, evaluation of CARS bandwidths and lineshifts resuited in a relatively precise temperature determination. The advantages of a CARS-based SF 6 thermometer are discussed in detail.

Stability of excited frequencies in a doubly resonant parametric oscillator

The problem of stability of excited frequencies is considered for a ring doubly-resonant optical parametric oscillator. The theory developed is based on the fixed field approximation used to analyze the interaction of waves on the tip of resonator cavity. It is shown that the excited frequency fluctuations arising due to resonator parameter variations can be largely suppressed. The suppression coefficient of technical fluctuations can be equal to 103 and more.

Focusing of picosecond x-ray pulses on the target at power densities up to 1 GW cm-2

The x ray emission from femtosecond laser-driven plasma has been investigated using spherical multilayered mirrors. Different laser pulse widths have been used. The conditions required to produce high intensity x ray emission (up to 1011 W cm-2) from H-like excited ions are discussed.

Possibility of ultrahigh shock-pulse generation by radiation pressure of superintense femtosecond light bursts

The conditions for shock-wave generation by UV light pressure are examined. It is shown that in the nonrelativistic regime of laser intensities 7 1018 W/cm2 < I < 7 1020 W/cm2 the radiation pressure can exceed thermokinetical pressure of hot electrons. In a time scale less than 10 fs, the formation of shock-pulse with Gbar pressure can be achieved.

Generation of ultrashort surface electromagnetic waves by diffraction of frequency-modulated laser pulses on periodical surface relief

It is well known that the interaction of laser beams with periodically corrugated surfaces (e.g., with diffraction gratings) can have a resonant character and can be accompanied by the strong local fields enhancement, suppression of the specular reflection, and anomalous high absorption of light. These effects are known as Woods anomalies. Previously we have theoretically investigated the peculiarities of these anomalies, when the ultrashort (pico- and femtosecond) regular laser pulses are incident upon a corrugated surface. In this paper, we consider the interaction of the frequency-modulated (chirped) laser pulses with gratings. The effect of the resonant excitation of surface electromagnetic waves (SEW) with a high amplitude and a duration less than that of the incident pulse is predicted. It can be considered as a method for the ultrashort powerful SEW generation. Different specific features of the Woods anomalies, such as transformation of the specular reflected pulse and anomalous high ultrafast input of the radiation energy into the surface, are analyzed.