Oleg V. Palashov

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.

Faraday Rotators With Short Magneto-Optical Elements for 50-kW Laser Power

Faraday rotators with short magneto-optical elements are created and experimentally studied. The magneto-optical elements are made three to four times shorter either by cooling them to nitrogen temperatures or by increasing the magnetic field. These ways are shown to increase maximum average laser power passing through the Faraday isolators up to 50 kW

High-power Faraday isolators based on TAG ceramics

The Faraday isolator based on a new magneto-optical medium--TAG (terbium aluminum garnet) ceramics was implemented and investigated experimentally. The magneto-optical element was temperature-stabilized using water cooling. The device provides a stable isolation ratio of 38 dB at 300 W laser power. Estimates show high performance of the device at a kilowatt laser power.

Improving characteristics of Faraday isolators based on TAG ceramics by cerium doping

A Faraday isolator (FI) based on a new magneto-optical medium-Ce:TAG ceramics-has been fabricated and studied in experiments. Compensation of thermally induced depolarization in the FI increases the isolation ratio from 31 to 39 dB at the laser power of 300 W. Estimates predict stable operation of the device with kilowatt laser power.

Suppression of self-induced depolarization of high-power laser radiation in glass-based Faraday isolators

Light absorption in optical elements of Faraday rotators results in a nonuniform cross-sectional temperature distribution that leads to depolarization of laser radiation and, consequently, limits the isolation ratio of optical Faraday isolators. We show experimentally that the influence of the temperature dependence of the Verdet constant on the isolation ratio is negligibly small when compared with the influence of the photoelastic effect. We also present two novel methods of optical isolation that significantly reduce the depolarization caused by the photoelastic effect and increase the isolation ratio by two orders of magnitude in comparison with the conventional method. Our results confirm the possibility of magneto-optical glass-based Faraday isolators with isolation ratios of 30 dB for average laser powers of hundreds of watts.

Compensation of thermally induced depolarization in Faraday isolators for high average power lasers

A compensation scheme for thermally induced birefringence in Faraday isolators is proposed. With the use of this scheme a 36-fold increase of the isolation degree was attained in experiment. A comparative analysis of the considered scheme and the earlier Faraday isolator schemes with high average radiation power is performed. A method for optimizing the earlier Faraday isolator scheme with birefringence compensation is developed.

Terbium gallium garnet ceramic Faraday rotator for high-power laser application

A terbium gallium garnet (TGG) ceramic Faraday rotator (FR) with an isolation ratio of 33 dB was demonstrated at a laser radiation power of 257 W. This FR can be equipped with a large optical aperture by using ceramics technology to prevent laser damage at high-energy pulse operation. The thermal lens of a 257 W laser with a beam diameter of 2.6 mm had a focal length of 9.5 m, which is easily corrected using a spherical lens to suppress the undesirable effects of thermal lensing. The rotation angle of the FR was stabilized by water cooling. The results indicate that the TGG-ceramic-based FR is suitable for high-energy laser systems with high repetition rates.

Magnetoactive media for cryogenic Faraday isolators

We analyzed a number of optical media, such as GGG, Nd:YAG, Yb:YAG, fused silica, CaF2, Yb:CaF2, and CdMnTe, that have not been used, to our knowledge, in the cryogenic Faraday isolator (FI) before. The temperature dependence of the Verdet constant and thermo-optical constants was experimentally investigated for λ=1.07 μm. We calculated the magneto-optical figure-of-merit and assessed the feasibility of using FI media with multikilowatt average laser power.

Study of the thermo-optical constants of Yb doped Y 2 O 3 , Lu 2 O 3 and Sc 2 O 3 ceramic materials

Thermally induced depolarization and thermal lens of three Konoshima Chemical Co. laser-ceramics samples Yb(3+):Lu(2)O(3)(C(Yb) ≈ 1.8 at.%), Yb(3+):Y(2)O(3)(C(Yb) ≈ 1.8 at.%), and Yb(3+):Sc(2)O(3) (C(Yb) ≈ 2.5 at.%) were measured in experiment at different pump power. The results allowed us to estimate the thermal conductivity of the investigated ceramic samples and compare their thermo-optical properties. The thermo-optical constants P and Q and its sign measured for these materials at the first time.