Anatoly Poteomkin

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.

Compensation of thermally induced modal distortions in Faraday isolators

Two methods of compensation of thermal lensing in high-power terbium gallium garnet (TGG) Faraday isolators have been investigated in detail: compensation by means of an ordinary negative lens and compensation using FK51 Schott glass possessing a negative dn/dT. Key thermooptic constants for TGG crystals and FK51 glass were measured. We find that the contribution of the photoelastic effect to the total thermal lens cannot be neglected for either TGG or FK51. We define a figure of merit for compensating glass and show that for FK51, an ordinary negative lens with an optimal focus is more efficient, but requires physical repositioning of the lens for different laser powers. In contrast, the use of FK51 as a compensating element is passive and works at any laser power, but is less effective than simple telescopic compensation. The efficiency of adaptive compensation can be considerably enhanced by using a compensating glass with figure of merit more than 50, a crystal with natural birefringence or gel.

100-TW Femtosecond Laser Based on Parametric Amplification

In experiments on the parametrical amplification of femtosecond pulses in wide-aperture DKDP crystals, a power of more than 100 TW has been reached, which is much higher than the record level achieved in such lasers. The energy efficiency obtained for the parametric amplifier is equal to 27%. The energy of a 72-fs pulse is equal to 10 J.

Compact 300-J/300-GW Frequency-Doubled Neodymium Glass Laser—Part II: Description of Laser Setup

All the basic elements of a 300 J/1 ns Nd:glass laser with high-efficiency (70%) frequency conversion are described in detail. These include a seed laser, a system shaping the spatial structure of the beam, a six-cascade amplifier based on neodymium phosphate glass rods 10-100 mm in diameter, and a second-harmonic generator on a DKDP crystal with ooe interaction. Reliable and easy operation guaranteed long-term functioning of the laser as a pump for the output cascade of a chirped pulse parametric amplifier in a petawatt laser complex.

Use of self-focusing for measurements of ultrasmall (less than λ/3000) wave-front distortions

Results of the use of self-focusing in Kerr liquids for the measurement of small wave-front distortions transmitted through a transparent optical sample are presented. Using controlled self-focusing to decrease the spot size of the deflected beam, we have been able to improve the measurement resolution by an order of magnitude compared with that achieved with a conventional Hartmann detector. We examine a variety of materials to determine the optimal nonlinear medium and demonstrate measurements of absolute wave-front deviations at the level of λ/3000. A prototype of a new device, the scanning nonlinear Hartmann sensor, is described.

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.

Generation of 3D ellipsoidal laser beams by means of a profiled volume chirped Bragg grating

A method for shaping photocathode laser driver pulses into 3D ellipsoidal form has been proposed and implemented. The key idea of the method is to use a chirped Bragg grating recorded within the ellipsoid volume and absent outside it. If a beam with a constant (within the grating reflection band) spectral density and uniform (within the grating aperture) cross-section is incident on such a grating, the reflected beam will be a 3D ellipsoid in space and time. 3D ellipsoidal beams were obtained in experiment for the first time. It is expected that such laser beams will allow the electron bunch emittance to be reduced when applied at R± photo injectors.

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.

Laser Driver for a Photoinjector of an Electron Linear Accelerator (February 2014)

The presented laser driver for a photoinjector of an electron linear accelerator delivers 10-ps long laser pulses with the energy of 1.85 μJ at the wavelength of 262 nm. Laser pulses irradiating with the repetition rate of 10 MHz form the rectangular 800-μ s long pulse trains with 18.5-W mean power inside them. The pulse train repetition rate is 10 Hz. Short-lived absorption centers accumulating in BBO fourth-harmonic generator crystal cause significant distortion of the pulse train envelope. The envelope remains rectangular due to precompensating of these distortions in the fiber acousto-optical modulator with fast varying transmission.

Adaptive compensation of thermal lens in Faraday isolators

Positive thermal lens in optical element (Faraday isolator in our case) produced by absorption of high power radiation was experimentally compensated with negative thermal lens in DKDP sample self-adaptive to different radiation powers.