Upgrading the front end of the petawatt-class PEARL laser facility.

A new front-end laser system with optical synchronization of chirped femtosecond and pump pulses for the petawatt laser complex PEtawatt pARametric Laser (PEARL) has been developed. The new front-end system provides a broader femtosecond pulse spectrum, temporal shaping of the pump pulse, and a significant increase in the stability of the parametric amplification stages of the PEARL.

Temporal compression of high-power IR laser pulses in a KDP crystal.

It is shown that a KDP crystal can be used for temporal compression of powerful pulses of the near-IR range. A method of searching for laser beam and crystal parameters suitable for compression is proposed. Temporal compression of laser pulses at a central wavelength of 1034 nm from 266 fs to 94 fs during propagation along the optical axis in a 21 cm thick KDP crystal is demonstrated experimentally.

Shaping of picosecond laser pulses with THz intensity modulation in the infrared, visible, and ultraviolet ranges.

The methods of shaping picosecond laser pulses with periodic intensity modulation tunable in frequency and depth are considered. Schemes for shaping modulated pulses "in-line" and with one output port are proposed. A picosecond modulation of the time envelope for IR laser pulses using a polarization interferometer is demonstrated experimentally. Shaping of modulated laser pulses of the UV range is shown by numerical modeling. The possibility to control the modulation depth of the fourth harmonic under the combined impact of material dispersion and nonlinear conversion in a classical collinear scheme of the fourth harmonic generation without distortion of the 3D pulse shape is demonstrated.

Highly efficient fourth harmonic generation of broadband laser pulses retaining 3D pulse shape.

A method for highly efficient fourth harmonic generation (FHG) retaining spatiotemporal intensity distribution of broadband chirped laser pulses is proposed. It is based on the use of pulses with linear frequency chirps of equal absolute magnitudes and opposite signs at the oo-e type noncollinear second harmonic generation. Fourth harmonic generation can by obtained by the classical method, since the second harmonic pulse is narrowband and spectrally limited. A possibility to retain the three-dimensional (3D) structure of the field at FHG with a conversion efficiency ∼60% is demonstrated by the numerical simulation of 3D pulses with a quasi-ellipsoidal intensity distribution.

Disk Yb:KGW amplifier of profiled pulses of laser driver for electron photoinjector.

We investigated a diode-pumped multipass disk Yb:KGW amplifier intended for amplifying a train of 3D ellipsoidal pulses of a laser driver for a photocathode of a linear electron accelerator. The multipass amplification geometry permitted increasing the energy of broadband (about 10 nm) pulses with a repetition rate of 1 MHz from 0.12 µJ to 39 µJ, despite large losses (two orders of magnitude) introduced by a beam shaper of 3D ellipsoidal beam. The distortions of the pulse train envelope were minimal due to optimal delay between the moment of pump switching on and arrival of the first pulse of the train.

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

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.

Propagation of laser radiation in a medium with thermally induced birefringence and 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 degrees polarization rotator or a Faraday mirror decreases with increasing B-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 degrees and the degree of polarization is less than for the linear one.

Spatial filters for high-peak-power multistage laser amplifiers.

We describe spatial filters used in a Nd:glass laser with an output pulse energy up to 300 J and a pulse duration of 1 ns. This laser is designed for pumping of a chirped-pulse optical parametric amplifier. We present data required to choose the shape and diameter of a spatial filter lens, taking into account aberrations caused by spherical surfaces. Calculation of the optimal pinhole diameter is presented. Design features of the spatial filters and the procedure of their alignment are discussed in detail.

200 TW 45 fs laser based on optical parametric chirped pulse amplification.

200 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 (DKDP) crystals providing 14.5 J energy in the chirped pulse at 910 nm central wavelength, and a vacuum compressor. The final parametrical amplifier and the compressor are described in detail. Scaling of such architecture to multipetawatt power is discussed.