Phase conjugation by stimulated Brillouin scattering represents a fundamentally promising approach for achieving power scaling of solid-state lasers. Following a summary of the power scaling problem and an overview of phase conjugation concepts, a review is presented of the application of phase conjugation to solid-state lasers. The author describes power scaling using demonstrated techniques for compensating static and thermally induced aberrations and depolarizations, as well as energy scaling by coherent coupling of multiple-gain media. Applications to diode-pumped lasers are discussed, as is a novel approach for power scaling of diode lasers themselves. Future research directions are indicated regarding conjugation fidelity at increasingly higher energies or with short-pulse and/or broadband lasers. >

A review of phase-conjugate solid-state lasers

The use of stimulated Brillouin scattering (SBS) for laser pulse compression by backward wave amplification in a tapered waveguide offers an attractive alternative to systems based on SRS for use with narrowband laser pulses. Almost one hundred percent conversion efficiencies may be achieved since it is not seriously limited by second Stokes production and with the added advantage that the Stokes pulse is a phase conjugate of the input pulse, under appropriate conditions. Due to the characteristically long damping times of Brillouin-active media, the SBS process is transient. In this regime, the tail of the Stokes pulse may experience a gain and loss modulation with the laser field resulting in a breakup of the Stokes pulse. This effect can be controlled by the geometric taper on the waveguide. A practical consideration of the scaling of a Brillouin compressor to high-power laser systems, notably KrF, is presented. Specific compressor configurations for the extraction of laser pulses in the nanosecond time scale are presented, and a survey of some promising compressor media indicate the practical possibility of accomplishing compression by SBS.

Laser pulse compression by stimulated Brillouin scattering in tapered waveguides

Reconstruction the phase front of a vortex laser beam is conducted by use of a Hartmann-Shack wavefront sensor. The vortex beam in the form of the Laguerre-Gaussian LG01 mode is generated with the help of a spiral phase plate. The new reconstruction technique based on measured wavefront gradients allows one to restore the singular phase surface with good accuracy, whereas the conventional least-squares approach fails.

Wavefront reconstruction of an optical vortex by a Hartmann-Shack sensor.

http://iopscience.iop.org/article/10.3367/UFNe.0181.201104m.0434/pdf

High-power lasers and their applications in high-energy-density physics studies

The acoustic decay time of hypersound generated by stimulated Brillouin scattering (SBS) has been measured in several heavy gases (Xe, SF 6 , CCIF 3 , C 2 F 6 ) over a range of pressures. A straightforward optical probing technique is used whereby the decay time can be measured directly with high precision. A theoretical formulation of the decay mechanisms in a polyatomic gas is presented, and it is shown both theoretically and experimentally that vibrational relaxation can become the major decay process at high gas density. The Brillouin gain coefficient and acoustic frequency are also experimentally determined or calculated for the gases investigated. Two Brillouin-active gases (CCIF 3 and C 2 F 6 ) with high Brillouin gains, which have not been studied previously, have been characterized. A study of the gas C 2 F 6 near its critical point showed a large variation of the acoustic velocity which reaches a minimum value in the vicinity of its critical density.

Direct measurement of the acoustic decay times of hypersonic waves generated by SBS

At present opportunity to apply phase conjugation phenomenon to laser facilities is widely investigated. High power nanosecond laser designs with SRS mirrors are considered as well. To discuss such designs it is very important. to obtain experimental data on performance of kilojoule class lasers, having aperture > 0.5 m, with phase conjugation. However, there is no publications in literature about experiments of such level. In our paper we present first experimental data, having been obtained on gas iodine laser with (0.4 - 1.2) m aperture and 6 kJ radiation energy in a nanosecond pulse in a single channel, using SBS mirror.

High-power nanosecond-pulse iodine laser provided with SBS mirror

Using the most complete in literature physical model of the non-steady-state stimulated Brillouin scattering (SBS), the numerical study is carried out of phase conjugation (PC) in the SBS-mirror that consists of an angular selector of Stokes radiation, an ordered raster of small lenses, a main focusing lens, and an SBS-cell. The ordered raster with controlled varying of its parameters allows to perform the effective angular filtering of non-conjugated Stokes components, to reduce the local light loads, and to avoid the competitive nonlinear effects. An optimal configuration of such SBS-mirror has been determined. It has the unique properties as compared with the current SBS-mirrors. It fixedly yields the PC quality that is near to an ideal (the PC coefficient is about of or more than 95%) at the selector transmittance 50 - 70% and any level of SBS saturation, i.e. any reflection coefficient. In the SBS-mirrors of different types the high PC quality in the focused beams takes place at the high reflection coefficients only that is difficult to realize as a rule. The first experimental data obtained at a Nd laser facility show the validity of the simulation results. The developed concept of SBS-mirror with unique properties can be applied for the improvement of wide class of industrial lasers.

Phase conjugation at SBS of pulse laser radiation using kinoform optics

Experimental investigation of the feasibility of application of the wavefront reversal phenomenon in stimulated Mandel'shtam-Brillouin scattering

The results of experimental investigations of wide-aperture (100 × 100 mm) plasma-electrode Pockels are presented Time characteristics, contrast, transmission factor, and optical uniformity of the cell are measured It has been found that the half-wave effective voltage of the cell is 10 kV, the duration of the transmission window can vary from 250 to 550 ns, its leading and trailing edges are 40–50 and 70–100 ns in duration, respectively, and the time of the cell plasma electrode formation is 40 ± 5 ns

Wide-aperture plasma-electrode pockels cell

The paper presents experimental results of operating an iodine laser with an SBS mirror. We have investigated generation dynamics, optical phase conjugation quality, and optimal conditions for achieving the high brightness of output radiation.© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Yu. V. Dolgopolov

Papers

High-power nanosecond-pulse iodine laser provided with SBS mirror

Phase conjugation at SBS of pulse laser radiation using kinoform optics

Experimental investigation of the feasibility of application of the wavefront reversal phenomenon in stimulated Mandel'shtam-Brillouin scattering

Wide-aperture plasma-electrode pockels cell

Generation of radiation of high brightness in gas lasers with SBS mirror and kinoform optics