Optical parametric amplifiers (OPAs) have the reputation of being average power scalable due to the instantaneous nature of the parametric process (zero quantum defect). This Letter reveals serious challenges originating from thermal load in the nonlinear crystal caused by absorption. We investigate these thermal effects in high average power OPAs based on beta barium borate. Absorption of both pump and idler waves is identified to contribute significantly to heating of the nonlinear crystal. A temperature increase of up to 148 K with respect to the environment is observed and mechanical tensile stress up to 40 MPa is found, indicating a high risk of crystal fracture under such conditions. By restricting the idler to a wavelength range far from absorption bands and removing the crystal coating we reduce the peak temperature and the resulting temperature gradient significantly. Guidelines for further power scaling of OPAs and other nonlinear devices are given.
© 2013 Optical Society of America
Original Manuscript: December 19, 2012
Revised Manuscript: January 28, 2013
Manuscript Accepted: January 29, 2013
Published: February 27, 2013
Jan Rothhardt, Stefan Demmler, Steffen Hädrich, Thomas Peschel, Jens Limpert, and Andreas Tünnermann, "Thermal effects in high average power optical parametric amplifiers," Opt. Lett. 38, 763-765 (2013)