Evgeniy A. Mironov

Faraday isolator based on TSAG crystal for high power lasers

A Faraday isolator based on a new magneto-optical medium, TSAG (terbium scandium aluminum garnet) crystal, has been constructed and investigated experimentally. The device provides an isolation ratio of more than 30 dB at 500 W laser power. It is shown that this medium can be used in Faraday isolators for kilowatt-level laser powers.

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.

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.

Investigation of thermo-optical characteristics of magneto-active crystal Na(0.37)Tb(0.63)F(2.26).

Thermo-optical characteristics of a new magneto-active material, Na(0.37)Tb(0.63)F(2.26) crystal, were investigated in this Letter. This crystal has a high value of magneto-optical figure-of-merit and negative optical anisotropy parameter that makes it a promising material for development of Faraday isolators for high-power lasers; in particular it gives opportunities for the realization of new schemes of optical isolators.

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.

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.

Cryogenically cooled CeF3 crystal as media for high-power magneto-optical devices

The thermally induced depolarization and Verdet constant of CeF3 crystals-their most important characteristics-have been studied in the 79-293 K temperature range. It has been found that thermal effects reduce substantially upon cooling down to 79 K and the Verdet constant grows in inverse proportion to the temperature. It was shown that CeF3 crystals are not inferior to TGG as a medium for Faraday isolators, including cryogenic ones.

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.

Faraday isolators based on TSAG crystal for multikilowatt lasers

With the laser technology being actively developed and the average power of both continuous wave and repetitively pulsed lasers steadily growing, the problem of reducing thermal effects occurring in various optical elements due to light absorption is becoming ever more important. A Faraday isolator (FI) is one of the optical devices that are most influenced by thermal self-action because of the relatively strong absorption (∼10−3 cm−1) in the magneto-optical elements (MOEs). The nonuniform temperature distribution induced by absorption gives rise to linear birefringence (photoelastic effect), in addition to the Faraday effect, and transmitted beam wavefront distortions (thermal lensing). In high-power lasers the degree of isolation is limited by the thermally induced depolarization.