Aleksey Starobor

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.

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.

Thermo-Optical and Magneto-Optical Characteristics of Terbium Scandium Aluminum Garnet Crystals

Magnetoactive materials are of considerable current interest, primarily for applications in nonreciprocal Faraday devices used for polarization control, optical isolation, optical switching, and modulation. The need for such devices is growing with laser power enhancement. They reduce risk of self-excitation of the amplifiers and optical elements damage and are a handy tool for organizing multipass schemes. However, at high average power of radiation these devices are subject to thermally induced effects that impair their operability and lead to increased losses and to the formation of phase distortions in the transmitted radiation. One of the methods to reduce thermally induced effects is to use in Faraday devices new magnetoactive materials with better thermo-optical properties. This paper is devoted to the study of thermo-optical and magneto-optical characteristics of a unique magnetoactive material-a terbium scandium aluminum garnet (TSAG) crystal. The TSAG has an extraordinary value of optical anisotropy parameter ξ, a Verdet constant 25% higher than the traditionally used terbium gallium garnet crystal and the highest magneto-optical figure-of-merit known in magnetoactive materials at the moment.

Thermo-optical properties of terbium-aluminum garnet ceramics doped with silicon and titanium

The Verdet constant and thermo-optical characteristics of a Si-doped and Ti-doped terbium aluminum garnet ceramics have been investigated. It is shown that the Verdet constant of the samples is ∼40% higher than that of TGG ceramics at 1064 nm. The best samples of Si:TAG have magneto-optical figures of merit more than 1.5 times greater than those of TGG ceramics. Si:TAG is better than TGG ceramics as a medium for high-power Faraday isolators.

Compensation of polarization distortions in Faraday isolators by means of magnetic field inhomogeneity

We propose a new type of Faraday isolator with compensation of the azimuthally symmetric component of polarization distortions by means of magnetic field inhomogeneity. The depolarization was attenuated in experiments by a factor of 7.

Faraday rotator based on TSAG crystal with orientation

A Faraday isolator (FI) for high-power lasers with kilowatt-level average power and 1-µm wavelength was demonstrated using a terbium scandium aluminum garnet (TSAG) with its crystal axis aligned in the <001> direction. Furthermore, no compensation scheme for thermally induced depolarization in a magnetic field was used. An isolation ratio of 35.4 dB (depolarization ratio γ of 2.9 × 10-4) was experimentally observed at a maximum laser power of 1470 W. This result for room-temperature FIs is the best reported, and provides a simple, practical solution for achieving optical isolation in high-power laser systems.

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.

Thermal effects in the DKDP Pockels cells in the 215–300 K temperature range

The thermal and electro-optical effects in Pockels cells with deuterated potassium dihydrogen phosphate (DKDP) crystals in the 215-300 K temperature range were investigated. Half-wave voltage decreases linearly with cooling, thereby it reduces seven times (up to 1 kW) with cooling to 215 K. The optical power of the thermally induced lens falls twice on cooling to 215 K from 300 K; thermally induced depolarization is almost independent of temperature and determined by input radiation power. A significant reduction of the thermally induced depolarization in a DKDP crystal with the axis inclined to the polarization plane of the beam was demonstrated numerically and experimentally. Thus, the DKDP crystals cooled to 215 K allow the creation of a low-voltage Pockels cell working with a high average and peak laser power.