560 TW peak power has been achieved experimentally using a Cr:forsterite master oscillator at 1250 nm, a stretcher, three optical parametrical amplifiers based on KD*P crystals providing 38 J energy in the chirped pulse at 910 nm central wavelength, and a vacuum compressor providing 43 fs pulse duration. To our knowledge, it is a world-record OPCPA system and one of the five most powerful laser systems currently available.

https://iopscience.iop.org/article/10.1002/lapl.200710008/pdf

Compact 0.56 Petawatt laser system based on optical parametric chirped pulse amplification in KD*P crystals

Laser-beam shaping and suppression of beam self-focusing in high-peak-power Nd:glass laser systems are discussed. The role of Fresnel diffraction at apertures at the laser facility as the source of dangerous spatial scales for small-scale self-focusing is illustrated. Methods of the formation of super-Gaussian laser beams for suppressing diffraction ripples on the beam profile and their self-focusing are presented. A brief outline of self-focusing as the primary nonlinear optical process limiting the brightness of Nd:glass laser installations is given. Methods for self-focusing suppression are presented.

Beam Shaping and Suppression of Self-focusing in High-Peak-Power Nd:Glass Laser Systems

We consider a problem of laser radiation propagating in a medium with birefringence of two types: linear birefringence independent of intensity and polarization, and intensity and polarization dependent circular birefringence caused by cubic nonlinearity It is shown theoretically and experimentally that the efficiency of the broadly employed method of linear depolarization compensation by means of a 90° polarization rotator decreases with increasing В-integral (nonlinear phase incursion induced by cubic nonlinearity) The accuracy of polarization transformation by means of a half-wave and a quarter-wave plate also decreases if В > 1 By the example of a λ/4 plate it is shown that this parasitic effect may be suppressed considerably by choosing an optimal angle of inclination of the optical axis of the plate

Theoretical and experimental study of laser radiation propagating in a medium with thermally induced birefringence and cubic nonlinearity.

The boundary problem on the development of a smallscale instability of arbitrarily polarised plane waves is solved. The influence of polarisation on the spatial-perturbation gain is analysed. The maximally allowable (i.e., causing no destruction of a nonlinear medium) average intensity at a specified input noise is determined for arbitrary polarisation.

Small-scale instability of elliptically polarised waves in a medium with cubic nonlinearity

A system of differential equations describing, neglecting diffraction, the propagation of laser radiation in a medium with birefringence and cubic nonlinearity is derived. It is shown that the efficiency of depolarization compensation by means of a 90° polarization rotator or a Faraday mirror decreases with increasing В-integral (nonlinear phase incursion). Comparison of the effectiveness of the considered method in the case of incident linear and circular polarization showed that for the circular polarization the optimal angle of polarization rotator is different from 90° and the degree of polarization is less than for the linear one.

Propagation of laser radiation in a medium with thermally induced birefringence and cubic nonlinearity.

A theoretical and experimental investigation is made of the suppression of small-scale self-focusing in high-power solid-state laser systems with repeaters by using circular polarization. The improvement in the output focused energy obtained experimentally for circular polarization as compared to that for linear polarization (~ 1.5 times higher) shows good agreement with the calculated value.

V I Kryzhanovskiĭ

Papers

Use of circularly polarized optical beams to suppress self-focusing instability in a nonlinear cubic medium with repeaters