302 W quasi-continuous cascaded diamond Raman laser at 1.5 microns with large brightness enhancement

We report a second Stokes diamond Raman laser at 1.49 μm capable of high power and large-scale-factor brightness enhancement. Using a quasi-continuous 1.06 μm pump of power 823 W (0.85% duty cycle) and M² up to 6.4, a maximum output power of 302 W was obtained with an M² = 1.1 providing an overall brightness enhancement factor of 6.0. The pulse length of ~210 μs was selected to ensure operation was representative of steady-state continuous lasing conditions in the diamond bulk. Accompanying theoretical calculations indicate that even more strongly aberrated pumps may be used to efficiently generate high beam quality output and with higher brightness enhancement factors. This diamond-based beam conversion technique addresses needs for high brightness and efficient eye-safe sources using low-brightness 1 μm pumps and reveals a widely-applicable route to practical high brightness lasers of increased wavelength range.