Intracavity frequency doubling of μs Alexandrite laser pulses

Intracavity second harmonic generation (SHG) with a three mirror folded cavity configuration was investigated with a flashlamp pumped, Q-switched Alexandrite laser. We therefore used different nonlinear optical crystals to convert the fundamental 750 nm radiation into the near UV spectral range (375 nm). The laser pulses were stretched into the μs time domain by an electronic feedback system regulating the losses of the resonator. We investigated the conversion efficiency for different pulse lengths as well as the effect of pulse-lengthening due to the nonlinearity of the intracavity losses introduced by the optical crystal used. Working with BBO-crystals, we were able to achieve a second harmonic output of 25 mJ per pulse at 375 nm with a temporal rectangular pulse of 1 μs in length and a stable nearly Gaussian shaped beam profile.