Victor Zelenogorsky

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.

High-precision methods and devices for in situ measurements of thermally induced aberrations in optical elements

An optical system that comprises two devices for remote measurements, a broadband optical interferometer and a scanning Hartmann sensor, is described. The results of simultaneous measurements with both devices and the results of numerical modeling of sample surface heating are presented.

Experimental study of thermal lens features in laser ceramics

Thermal lens measurements were made by means of a high-accuracy phase shift interferometer that combines a lambda/1000 sensitivity and 10 microm transverse resolution. The effect of random small-scale modulation in thermally induced phase distortion predicted earlier was proved experimentally. The statistical parameters of modulation were measured depending on heating power for two different ceramic samples. The experimental data agree well with results of numerical simulation.

High-vacuum-compatible high-power Faraday isolators for gravitational-wave interferometers

Faraday isolators play a key role in the operation of large-scale gravitational-wave detectors. Second-generation gravitational-wave interferometers such as the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) and Advanced Virgo will use high-average-power cw lasers (up to 200 W) requiring specially designed Faraday isolators that are immune to the effects resulting from the laser beam absorption–degraded isolation ratio, thermal lensing, and thermally induced beam steering. In this paper, we present a comprehensive study of Faraday isolators designed specifically for high-performance operation in high-power gravitational-wave interferometers.

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.

Use of scanning Hartmann sensor for measurement of thermal lensing in TGG crystal

Investigations of thermal effects caused by absorption of laser radiation in Faraday isolators and Faraday mirrors are becoming more important. A most promising medium for Faraday devices in the wavelength range of 600-1200 nm is the terbium gallium garnet (TGG) crystal. In order to measure its thermo-optic constants (which are unknown) we used a scanning Hartmann sensor technique. This technique can easily and inexpensively measure wavefront distortions induced by optical elements to within 2nm.

3D ellipsoidal beam shaping in laser drivers for photoinjectors

Ellipsoidal laser pulses with central wavelength of 1030 nm and duration of 40 ps were obtained. It is expected that after conversion into the fourth harmonic this will reduce appreciably emittance of the electron beam, injected by the laser.

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.

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.

YLF rods thermal lens astigmatism

Thermal effects in optical mediums became more and more important in applied optics because of quick and steady grow of average power of modern lasers. Radiation power is so high that phase distortions caused by thermal lensing effects became important for achieving lasers resonators stability. In this paper we discuss interesting experimental results for YLF crystal: high anisotropy and high astigmatism of thermal lens in acutted YLF rods. The first effect is more or less predictable because YLF is uniaxial crystal. But high astigmatism of thermal lense is unexpected and is not explained in literature so far. Astigmatism is so high that phase distortions profile for perpendicular directions can change its sign [1–3]. Unfortunately in most papers the reason of thermal lens astigmatism is not discussed. At some papers there is a try to explain this by thermal conductivity anisotropy and as a result - non-symmetric temperature distribution but this effect is unable to change the sign of the lens.