Energy Scaling, Second Stokes Oscillation, and Raman Gain-Guiding in Monolithic Diamond Raman Lasers

Energy scaling of the first Stokes oscillation is compared in micro-lensed and plane-plane monolithic diamond Raman lasers under 532-nm pumping. A maximum Raman pulse energy of 92 μJ at 573 nm was achieved with the micro-lensed device, whereas in a plane-plane configuration, the maximum Raman pulse energy was 3.1 mJ. The second Stokes generation at 620 nm in 2 and 1 mm long micro-lensed monolithic diamond Raman lasers is also reported. The best conversion efficiency from the pump at 532 nm, namely, 63%, was observed in a 2 mm long crystal at the pump pulse intensity of 4.5 GW/cm
²
. By measuring the output Raman laser beam caustic, it was found that the second Stokes intracavity beam radius at the output coupler of the micro-lensed device is at least two times smaller than that expected from the ABCD matrix calculations of the resonator mode. A Raman gain-guiding mechanism is suggested to explain this difference.