Generation of high-power single-frequency 3975 nm laser with long lifetime and perfect beam quality in an external enhancement-cavity with MgO-doped PPSLT

Continuous-wave single-frequency high power 397.5 nm laser with long lifetime and perfect beam quality is one of the essential resource to generate the squeezed and entanglement states of optical beams resonant with D 1 line of Rubidium atoms at 795 nm. In this paper, We present the experimental generation of single-frequency high power 397.5 nm ultra-violet (UV) laser with long lifetime and perfect beam quality by using periodically poled MgO-doped stoichiometric lithium tantalate (MgO:PPSLT) crystal as the frequency doubler in an external enhancement ring cavity. When the transmission of the input coupler is 5.5%, the maximal output power of single-frequency 397.5 nm UV laser of 407 mW is obtained under the incident pump power of 1.9 W with the corresponding conversion efficiency of 22.8%. When the output power is 290 mW, the measured power stability and the beam quality are lower than 0.28% and 1.02, respectively. Moreover, any damage is not observed in our experiment which lasts about 1 year.