Major results

1. A.Z. Grasiuk, I.G. Zubarev, V.F. Efimkov, V.G. Smirnov, High-power SRS lasers – coherent summators (the way it was). Quantum Electron., 42(12), 1064–1072 (2012).

   The history of the research works performed under the guidance of N.G. Basov and aimed at developing high-energy lasers – coherent summators (CSs) – based on stimulated Raman scattering (SRS) in liquid nitrogen and liquid oxygen is reported. The work was performed jointly by researchers of FIAN [the Laboratory of Quantum Radiophysics (LQRP)] and VNIIEF. Many problems were solved as a result of these studies. Liquid nitrogen and oxygen were found to be optimal active media for high-power SRS lasers with high energy per pulse. A method for purifying these cryogenic liquids from micro- and nanoimpurities was developed, which made it possible to eliminate nonlinear loss of pump radiation and converted radiation in the active medium and ensure effective operation of SRS lasers – coherent summators (SRSL CSs) with high output energy. Cryogenic cells providing high optical homogeneity of liquid nitrogen and oxygen were developed, which ensured low (at a level of 0.1 mrad) divergence of converted radiation with high energy density. Raster focusing systems providing optimal concentration of pump radiation in the active medium were designed. These studies resulted in the development of high-power high-energy SRSL CSs with a low beam divergence, based on liquid nitrogen (λS = 1.89 μm) and liquid oxygen (λS = 1.65 μm), with pumping by explosively pumped iodine lasers (EPILs) (λp = 1.315 μm). The characteristics of the SRSL CSs developed were record for that time (the end of 1960s and the beginning of 1970s): energy up to 2.5 kJ per 10-μs pulse, beam divergence ~10-4 rad, and beam energy density of several hundreds of J cm-2.

2. I.M. Bel’dyugin, V.F. Efimkov, I.G. Zubarev, S.I. Mikhailov, V.B. Sobolev, Amplification of Stokes signals with phase conjugation by combined laser and SBS amplifiers. Quantum Electron., 37(1), 43–48 (2007).

   Various schemes for amplification of Stokes signals are investigated. Some new systems, such as an SBS amplifier in the transient amplification regime and a combined laser amplifier–SBS amplifier, are proposed and realised. Conditions are found under which amplification is accompanied by small distortions of the spatial structure of a signal. A two-pass system for small-signal amplification with phase conjugation is developed by using a PC mirror in the combined amplification system. The gains up to 1016 were obtained for the phase conjugation quality ~80%, the output energy ~1 J, and pulse duration ~30 ns.

3. V.I. Kovalev, R.G. Harrison, A.M. Scott, 300 W quasi-CW diffraction limited output from a diode pumped Nd:YAG MOPA with fiber phase conjugate SBS mirror, Opt. Lett., 30(11) (2005).

   A master oscillator power amplifier system comprising a cw Nd:YAG master oscillator, a quasi-cw diode-pumped power amplifier, and a fiber-based stimulated Brillouin scattering phase-conjugate mirror are reported. A 12-pass amplifier configuration is employed to achieve high gain in a small-length slab amplifier. Residual and pump-induced optical inhomogeneities in the slab are corrected by the fiber phase conjugator to achieve diffraction-limited output beam quality. 300 W quasi-cw output and a maximal attainable gain of ∼150 for the system are obtained.

4. I.M. Bel’diugin, V.F. Efimkov, I.G. Zubarev, S.I. Mikhailov, Amplification of small Stokes signals in the transient regime of stimulated Brillouin scattering. J. Russian Laser Res., 26(1) (2005).

   Amplification of small signals was investigated both experimentally and theoretically. The theoretical analysis was carried out in constant pump  approximation at consideration of  temporal structures of the interacting pulses (unsaturated regime). With pumping pulse duration of the order of acoustic phonon lifetime, the duration  of the output Stokes signal in the large gain regime  was shown to be less than that of the pumping pulse by only a half. To achieve the maximum gain, the pumping pulse should be delayed with respect to the input Stokes pulse by a time interval of the order of the  acoustic phonon lifetime.  Energy gains ~ 2·109 were experimentally achieved with an input signal energy of the order of 10–11 J.

5. I.M. Bel’dyugin, V.B. Gerasimov, V.F. Efimkov, I.G. Zubarev, N.A. Makarov, S.I. Mikhailov, Method for obtaining diffraction-limited incoherent images of objects observed through a turbulent atmosphere. Quantum Electron., 35(9), 873–878 (2005).

   A new approach is developed for obtaining diffraction-quality incoherent images of objects observed through a distorting optical medium. In particular, a method is proposed for achieving the diffraction limit  resolution , including the case of objects observed through a turbulent atmosphere, using comparatively cheap aberrational optical systems (including systems with sectional  apertures) without using any auxiliary adaptive devices. It is shown that the instrumental function of the atmosphere+telescope system can be reconstructed with the help of the radiation intensity distribution in an auxiliary plane, and then used for obtaining a diffraction-limited image of the observed remote object. Numerical simulation demonstrates the application of this method for identifying various objects by observing them through a turbulent atmosphere.

6. I.M. Bel’dyugin, A.A. Gordeev, V.F. Efimkov, I.G. Zubarev, S.I. Mikhailov, V.B. Sobolev, Loop SBS oscillator on a stationary nonlinear refractive index grating. Quantum Electron., 39, 12 (2009).

   A loop SBS oscillator is studied, in which pump radiation passed through  a nonlinear medium is directed backward to the medium. To increase the interaction length, a light guide is used. The feedback is obtained on a stationary nonlinear refractive index grating produced by the pump waves. The signal generated at the Stokes frequency in the loop propagates in the direction opposite to the pump and is amplified due to the classical backward SBS. Such an oscillator can be treated as a distributed feedback oscillator produced by the pump waves themselves.

7. A.A. Gordeev, V.F. Efimkov, I.G. Zubarev, S.I. Mikhailov, Phasing of Stokes radiation under shock excitation of stimulated Brillouin scattering, Quantum Electron.,41(11), 997–1002 (2011).

   Interaction of counterpropagating waves in Brillouin-active media has been analysed by numerical computation. The dynamics of the development of acoustic waves is described using a second order equation. It is shown that in the case of counterpropagating waves with sufficiently steep leading pulse edges (τf ≤ 3T2, where T2 is the acoustic phonon lifetime), SBS begins from the level of acoustic waves induced by shock excitation in the bulk of the active medium rather than from the spontaneous noise level. This mechanism determines the phase of the output Stokes wave, which is generated in the backward direction, by the phase of the wave with the highest input intensity, irrespective of the ratio of counterpropagating-wave frequencies.