Compression minimizes thermal lensing in disk laser

Diode-pumped solid-state lasers operating at TEM₀₀ are limited by degradation of beam quality induced by pump-induced thermal lensing. This was the driving force behind the development of the disk laser, in which heat is conducted one-dimensionally through the back disk face. But there are transverse thermal gradients even in disk lasers, and the gain crystal is susceptible to deformation. By clamping a disk laser between a thick sapphire window and a copper heat sink, researchers at the University of Toronto (Toronto, Ontario, Canada) and the University of Rochester (Rochester, NY) have successfully minimized thermal lensing through compression.

Applied pressure can, in theory, exactly cancel forces generated by pump-induced thermal expansion. The researchers fabricated a 1.3-µm-emitting Nd:YVO₄ (vanadate) laser having a 5 x 5 x 0.4-mm crystal and applied a pressure of just less than 700 MPa, pumping the laser with a 1.5-mm-diameter, fiber-coupled diode-laser array. The disk laser reached 19 W of TEM₀₀ output power (M² of 1.3)--limited by the pump, not by thermal lensing. An additional benefit is an increased thermal fracture limit. Using this technique, the researchers believe disk lasers can be scaled to greater than 100 W of TEM₀₀ output.