Diode-pumped continuous-wave and femtosecond Cr:LiCAF lasers with high average power in the near infrared, visible and near ultraviolet

Abstract

Abstract:We demonstrate continuous-wave (cw), cw frequency-doubled, cw mode-locked and Q-switched mode-locked operation of multimode diode-pumped Cr:LiCAF lasers with record average powers. Up to 2.54 W of cw output is obtained around 805 nm at an absorbed pump power of 5.5 W. Using intracavity frequency doubling with a BBO crystal, 0.9 W are generated around 402 nm, corresponding to an optical-to-optical conversion efficiency of 12%. With an intracavity birefringent tuning plate, the fundamental and frequency-doubled laser output is tuned continuously in a broad wavelength range from 745 nm to 885 nm and from 375 to 440 nm, respectively. A saturable Bragg reflector is used to initiate and sustain mode locking. In the cw mode-locked regime, the Cr:LiCAF laser produces 105-fs long pulses near 810 nm with an average power of 0.75 W. The repetition rate is 96.4 MHz, resulting in pulse energies of 7.7 nJ and peak powers of 65 kW. In Q-switched mode-locked operation, pulses with energies above 150 nJ are generated.

Passively Q-switched Cr:LiCAF laser with a saturable Bragg reflector

“…Some of this is due to the difficulty of mode-matching to the multimode pump beam. On the other hand, a cw slope efficiency of 32% [40] and 49% [41] were reported in similar MMD diode-pumped systems, while using a 10% Cr-doped LiCAF sample with ~0.3% passive loss and 5% Cr-doped LiCAF sample with ~0.1% passive loss, respectively. The relatively highly Cr-doped (7%) LiCAF sample in our study had an internal crack from earlier power scaling studies, and we believe that this increased the passive losses of the sample at hand to around 0.6%.…”

“…However, higher modulation depths will only be feasible in a system with improved gain, which could be achieved by using a lowly Cr-doped Cr:LiCAF sample (1-3%) with lower passive loss and reduced thermal issues. As described in [41], a lower Cr-doping could facilitate the usage of higher pump power levels via better distribution of heat load along the crystal length, which can then allow usage of an SBR with a larger modulation depth.…”