Thermal effects in eye-safe ring optical parametric oscillator based on KTiOPO 4 crystal

In eye-safe ring optical parametric oscillator (OPO) containing three KTiOPO 4 crystals the crystal placed first in the path of pump radiation is subjected to the strongest thermal distortion caused by idler absorption. For the 10-Hz 35-mJ OPO, thermally induced lenses generate an increase in the signal beam divergence by 10% and moderate decrease in the signal energy.