3 μm erbium laser with a SBS phase conjugating mirror

3 μm erbium lasers can be widely used in medical applications due to water absorption maximum at 3 μm. This allows cleaner cuts with smaller destruction of adjacent tissues. A power scaling of laser radiation in this wavelength range with maintaining good beam quality is very important to reach good surgically results. However, many difficulties exist to scale the output power of 3 μm erbium lasers. One of them results from thermal lensing in the active materials. To solve this problem, we have realized for the first time an Er:Cr:YSGG laser in a MOPA arrangement incorporating a SBS-cell as phase-conjugating mirror, where also a resonant reflector and a FTIR-shutter as Q-switch were used in the master oscillator. An optical isolator between the master oscillator and the power amplifier at 3 μm wavelength was constructed by using a self-made λ/4-plate and a polarizer based on silicon plates technology which function also as the outcoupling device for the phase conjugated beam. The phase-conjugating properties of the output beam were demonstrated by observing the profiles of both input and output beams. A SBS reflectivity of more than 40 % and a SBS threshold of below 200 kW were obtained in the CS 2 SBS-liquid. Our results demonstrate that SBS phase conjugation can be also applied for MOPAs with high beam quality of 3 μm radiation.