Thermal effects in high average power optical parametric amplifiers.

Area of Science:

• Nonlinear optics
• Laser physics
• Materials science

Background:

• Optical parametric amplifiers (OPAs) are known for average power scalability due to their instantaneous parametric process.
• However, thermal effects arising from absorption in nonlinear crystals pose significant challenges for high-power operation.

Purpose of the Study:

• To investigate the thermal load and resulting mechanical stress in high average power OPAs using beta barium borate crystals.
• To identify the sources of crystal heating and propose mitigation strategies for power scaling.

Main Methods:

• Experimental investigation of thermal effects in beta barium borate (BBO) based OPAs.
• Measurement of crystal temperature and mechanical stress under high average power pumping.
• Systematic variation of idler wavelength and crystal coating to assess their impact on thermal load.

Main Results:

• Significant crystal heating, up to 148 K, and mechanical tensile stress, up to 40 MPa, were observed due to absorption of pump and idler waves.
• Restricting the idler wavelength away from absorption bands and removing crystal coatings substantially reduced peak temperature and thermal gradients.
• These modifications mitigate the risk of crystal fracture.

Conclusions:

• Thermal load due to absorption is a critical limiting factor for average power scaling in OPAs.
• Careful selection of operating parameters, such as idler wavelength, and crystal surface treatments are crucial for mitigating thermal effects.
• The findings provide essential guidelines for advancing high average power OPAs and other nonlinear optical devices.