Generation Of Continuous-wave 194nm Laser By Fourth Harmonic Generation

Ultraviolet laser plays an important role in fine machining,damage detection,atomic spectrum and other fields due to its advantages of short wavelength and high photon energy.The 194nm radiation corresponds to the 6²S_1/2-6²P_1/2transition line of mercury ions,which is crucial for precision spectral researches based on mercury ions.In 2015,our group produced a 194nm continuous laser at milliwatt level by combining718nm laser and 266nm laser.However,the overall system is complex,and the locking of multistage optical cavity has high requirements on environment and system stability.The discovery of KBBF crystal and prism coupling technology make it possible to generate 194nm laser directly by second harmonic generation.The main work of this paper is to build a quadrupling frequency system,which generates a maximum power of 940m W continuous-wave laser and a 12.8m W continuous-wave laser of 194nm.A homemade 776nm semiconductor laser seeds a780nm tapered semiconductor amplifier with 3W output as the fundamental frequency light.A high damage threshold LBO crystal is used to generate a watt-level 388nm laser.Subsequently,a 12.8m W 194nm continuous-wave laser was generated by KBBF prism coupling device through cavity resonance enhancement,providing a high-quality light source for the development of mercury ion optical clock.The innovative work of this paper mainly includes:the thermal lens effect in the tapered amplifier was discovered,and the equivalent focal length of the thermal lens effect is estimated.A set of shaping scheme composed of cylindrical mirror,prism pair and lens is adopted,which effectively improved the coupling efficiency in the process of second harmonic generation.The optimum beam waist with different crystals is calculated.The influence of the size of the frequency doubling cavity on the laser mode parameters is analyzed.An asymmetric frequency doubling cavity was designed to reduce the size of the cavity while ensuring the separation of 194nm light.Based on the above improvements,a 194nm deep ultraviolet continuous laser based on KBBF crystal frequency doubling was realized for the first time in China.