Mikhail Martyanov

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.

Laser System for Generation 3D Ellipsoidal UV Pulses

An original laser system for implementation at DESY PITZ photoinjector to generate profiled UV optical pulses with energies exceeding 2 μJ with 28 ps pulse duration was designed and constructed.

High-power UV light generation in picosecond pulse trains

This paper focuses on the investigation of detrimental UV induced effects during fourth harmonic generation (FHG) in BBO crystals. An accumulation of partly recoverable UV two-photon induced optical defects has been observed in the 140 s train generated by frequency quadrupled 1.5 GHz Nd:YLF laser with about 300 W UV power per train, even for a relatively low peak pulse intensity of about 100 MW/cm2. BBO crystals with length of 4.2, 8.5 and 12 mm have been tested. In a shorter crystal less distortion have been observed for the same UV output power. Although the growth of optical defects is attributed to the UV two-photon absorption, the already accumulated defects lead to a linear absorption of green and UV co-propagating pulses which in turn results in train envelope degradation due to deterioration of a phase-matching and thermal beam distortion. The UV beam exhibited focusing behavior on a short distance (crystal length) which cannot be explained by temperature dependence of BBO refractive indexes. The UV beam focusing is addressed as a strong photo-elastic effect, caused by the stress induced by essentially non-uniform temperature distribution inside the beam propagation volume.

Cross-correlator for the diagnostics of 3D ellipsoidal shaped UV laser pulses for the future XFEL low-emittance photo-injector

Summary form only given. The European X-ray Free Electron Laser (XFEL) is being built at DESY in Hamburg. Its ultrashort X-ray flashes with extremely high peak and average brilliance are expected to allow unprecedented experiments with atomic resolution on femtosecond time scales. The Photo Injector test facility at DESY, Location Zeuthen (PITZ) is responsible for the developing of the electron source for the XFEL. The laser driven RF gun has to fulfill very challenging specifications on electron source performance for linac based FELs, namely it should provide electron bunches with high bunch charge (~1 nC) and extremely low transverse emittance (<; 1 mm mrad). The RF photo-injector drive laser pulse shaping is a key issue to achieve such a performance. It was theoretically shown [1] that the 3D ellipsoidal shape of the UV pulses driving the photo-injector is the optimal.

200MeV electron bunch generated by PEtawatt pARametric Laser (PEARL)

In this paper we discuss laser wake field acceleration experiments made at the PEtawatt pARametric Laser (PEARL). Using free 2mm and 5 mm gas jet without preplasma we generated electron beam with energy up to 260 MeV. The charge of quasimonoenergetic beams achieved 300 pC, angular divergence 0.2 degree. The special attention is paid for diagnostics which is adapted for low repetition rate systems with low output parameters stability.

Theoretical investigation of negative influence of the cubic nonlinearity and induced birefringence on developing and using contemporary PW lasers systems

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 B-integral (nonlinear phase incursion). Comparison of the considered method effectiveness 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.