Anton G. Vyatkin

Drastic reduction of thermally induced depolarization in CaF 2 crystals with [111] orientation

The key importance of the sign of the stress-optic anisotropy ratio for reducing thermally induced depolarization in cubic crystals with 432, 4¯3m and m3m symmetry is addressed. A simple method for measuring the stress-optic anisotropy ratio (including its sign) was proposed and verified in CaF<₂ and TGG crystals by experiment. The ratio at room temperature for the wavelength 1076 nm was measured to be -0.47 and + 2.25, respectively. In crystals with a negative value of this parameter thermally induced depolarization may be reduced significantly by choosing crystal orientation. In a CaF₂ crystal with the [111] orientation a 20-fold reduction of thermally induced depolarization as compared to the [001] orientation was obtained in experiment, which is very promising for using CaF₂ as an active element in high-average-power lasers.

Thermally induced scattering of radiation in laser ceramics with arbitrary grain size

Thermally induced beam distortions in laser ceramics with arbitrary grain size have been investigated. A model for the spatial spectral density of dielectric permeability variations was suggested. The average scattered intensity was calculated using the small disturbances method (theory of Rayleigh–Debye scattering). The direction pattern of the scattered field and the extinction coefficient have been obtained. The scattered power and the depolarization ratio fit with the corresponding values obtained in the geometric optics approximation in the range of its validity.

Thermal Effects in End-Pumped Yb:YAG Thin-Disk and Yb:YAG/YAG Composite Active Element

The small signal gain and phase and polarization distortions of laser radiation have been investigated theoretically and experimentally in end-pumped Yb:YAG thin-disk and Yb:YAG/YAG composite active element under nonlasing conditions. Comparison of experimental data with calculation results reveals an additional heat release whose negative influence is three times stronger than that of amplified spontaneous emission in the thin-disk active element.

Self-compensation of thermally induced depolarization in CaF 2 and definite cubic single crystals

Compensation of thermally induced depolarization in laser active elements at small birefringence without additional phase elements was proposed and observed experimentally. Requirements to the crystals were formulated. An order of magnitude reduction of depolarization degree was obtained experimentally. A further modification of the scheme was developed.

Thermally Induced Beam Distortions in Sesquioxide Laser Ceramics of m3 Crystal Class—Part II

In the first part of this paper, thermally induced polarization and phase distortions of a laser beam in cubic ceramics were calculated considering the specific features of photoelastic properties of 23 and m3 crystal classes. Here we use these quantities to calculate Strehl ratio and the integral of overlapping of the input and output beams both on passing one ceramic element as well as at the output of the scheme with the compensation of birefringence. The depolarization degree and the overlap integral are then compared with the distortions calculated earlier using the Rayleigh-Debye scattering theory method. The relative value of the distortion components inherent to 23 and m3 ceramics is assessed.

Measurements of Thermo-Optical Characteristics of Cubic Crystals Using Samples of Arbitrary Orientation

A method for measuring thermo-optical characteristics of cubic crystals having arbitrary known orientation has been developed. Unlike the traditional techniques, it does not demand samples of specified orientation that greatly expands the scope of its applications and frequently makes it indispensable when novel optical media should be investigated. Experimental verification of the technique using a well-studied TGG crystal shows a convincing agreement between the results obtained by the new and the conventional methods.

Thermally induced beam distortions in laser ceramics at strong birefringence

A new method of calculating quality parameters of a beam, which has passed through laser ceramics whose grains are large compared to the wavelength at an arbitrary value of thermally induced birefringence, has been developed. The intensity of a large-scale field in initial and orthogonal polarizations has been found. The results fully agree with the thermally induced distortions calculated by other methods. The intensity of a large-scale field was also obtained within the framework of the Rayleigh–Debye scattering theory for arbitrary size ceramic granules.

Sub-joule level high repetition rate cryogenic disk laser

Spectral and thermooptical properties, the stored energy and amplification in Yb: YAG disks are investigated at 77-300K temperature range. The current status of the laser system development with 0.5J output energy at 1kHz repetition rate is presented.

Compensation of Thermal Depolarization in CaF 2 with no Additional Phase Elements

Compensation of depolarization in lasers’ active elements at small birefringence without additional phase elements was proposed and experimentally observed. Requirements on the crystals were formulated. A further modification of the scheme was found.

Thermally Induced Depolarization in Sesquioxide Crystals of m3 Symmetry Class

Thermally induced depolarization degree in cubic crystals of classes 23 and m3 as a function of crystal orientation was investigated. Three new specific orientations were defined. The best and the worst orientations were determined.