TSAG-based cryogenic Faraday isolator

• Thermooptical characteristics of TSAG crystal were investigated in 90–300 K range.
• Optical power of the thermal lens in TSAG is reduced in 2.5 times on cooling to 80 K.
• Thermally induced depolarization in TSAG decreases in 18 times on cooling to 90 K.
• TSAG-based cryogenic Faraday isolator can operate at 400 kW laser power.

Thermooptical and magnetooptical properties of novel magnetoactive crystal terbium–scandium aluminum garnet were investigated at temperature range 80–300 K. It is shown that Verdet constant increases inversely proportional to temperature, and thermally induced depolarization, and the optical power of the thermal lens is reduced significantly with cooling from 290 K to 80 K. According to estimates, TSAG crystals in [1 1 1] orientation allow to create a cryogenic Faraday isolator provides a degree of isolation of 30 dB with the laser power exceeds ∼6 kW, it is estimated that the transition to the [0 0 1] orientation allows to provide degree of isolation of 30 dB at a laser power higher than 400 kW.