Adaptive compensation of thermally induced phase aberrations in Faraday isolators by means of a DKDP crystal

In this paper, we describe adaptive compensation of thermal lens in a Faraday isolator using a DKDP crystal. Thermal lens measurements were made with a modification of the conventional Hartmann sensor – a 2D scanning Hartmann sensor. Our experiments showed that a DKDP crystal does not influence the isolation ratio of Faraday isolator and efficiently compensates for thermal lens. The negative effect produced by the thermal lens is estimated as the amount of power losses from the original beam mode (Gaussian mode in our experiments). Without compensation the losses were measured to be about 25% for 45 W radiation power and were compensated to less than 0.5% by a negative thermal lens in a 5.5 mm-thick DKDP crystal. Numerical extrapolation of experimental data to a higher power range has shown that for the powers up to 150 W, power losses can be made less than 5%.