Dmitry S. Zheleznov

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.

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 properties and prospects of Ce:TAG and TGG magnetooptical ceramics for optical isolators for lasers with high average power

The prospective magnetooptical TGG, TAG and Ce:TAG ceramics for large-aperture Faraday isolators for lasers with average power more than 100W are compared. TGG ceramics is 1.5 times inferior to TGG crystals, whereas TAG ceramics is comparable with TGG crystals in maximum radiation power at the same isolation ratio. Optical power of their thermal lenses is also identical. Improvement of ceramics growth technologies and using doping for increasing Verdet constant is expected to additionally reduce thermal distortions in ceramics.

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.

Large-aperture Faraday isolator based on a terbium gallium garnet crystal.

Unique Faraday isolator based on a TGG single crystal with aperture diameter of 40 mm for high average power lasers has been fabricated and investigated experimentally. The device provides a stable isolation ratio over 30 dB for large-radius laser beams with kilowatt average power radiation typical for high-power applications.

Effect of paramagnetic magnetization in Faraday isolators

The influence of paramagnetic magnetization of magneto-optical elements on the characteristics of Faraday isolators is studied. The theoretical estimates confirmed by the experiment indicate that this effect should be taken into consideration, particularly when designing large-aperture and cryogenic Faraday isolators.

Drastic reduction of heat release in magneto-optical elements: new ways towards a 100 kW average power Faraday isolator

Faraday isolators with low heat release are created for high average power lasers. The heat release is reduced either by shortening the optical element (due to cooling to nitrogen temperatures or use of superconducting solenoids) or by employing non-traditional magneto-optical media with better thermo-optical properties. It is shown that the suggested ways make it possible to create a Faraday isolator for 100kW average power.