Combined dual-wavelength laser diode beam end-pumped single longitudinal mode Pr<sup>3+</sup>:LiYF<sub>4</sub> 360 nm ultraviolet laser

Abstract

In recent years, all-solid-state ultraviolet lasers have had widely potential applications in the fields of spectroscopy, biological analysis, precision manufacturing, optical data storage, high-resolution printing, medicine and lithography. The good monochrome of all-solid-state ultraviolet laser can improve the accuracy of spectral absorption measurement when used to detect specific proteins and reduce the laser spot diameter when used for high density data storage or acousto-optic deflector. In this paper, a combined dual-wavelength laser diode (LD) beam end-pumped single longitudinal mode Pr<sup>3+</sup>:LiYF<sub>4</sub> all-solid-state UV laser at 360 nm is presented. A V-folded cavity structure is used in the laser, which consists of a reflective volume Bragg grating (RBG) and a Fabry-Perot (F-P) etalon. The RBG is used as a wavelength selection and resonator reflector to narrow the width of spectral line. The F-P etalon is hybrid in the cavity, serving as a narrow-band filter, to achieve the single longitudinal mode. The lithium triborate crystal with critical type-I phase matching at room temperature is used for implementing the second-harmonic generation of the fundamental 720 nm laser and obtaining an efficient and compact ultraviolet laser at 360 nm. The optical resonator is simulated and analyzed by MATLAB software. Two experiments are conducted to compare the accuracy of central wavelength tuning by changing the temperature of F-P etalon and the angle of F-P etalon. The result shows that the change temperature of F-P etalon can achieve 0.165 pm/℃, showing that it is a better method. The structure of the laser is simplified and the anti-interference capability is improved in this way. It is different from mode competition method and the stability of single longitudinal mode laser output is increased. When the output power of LD at 444 nm is 1200 mW and that of LD at 469 nm is 1400 mW, a single longitudinal mode CW UV laser at 360 nm with output power as high as 112 mW is achieved. The optical-to-optical conversion efficiency is 4.3%, and the longitudinal linewidth of laser is 30 MHz. The measurements show that the edge suppression ratio is greater than 60 dB, the stability of root mean square (RMS) of output power in 4 h is better than 0.5%, the frequency shift in 1h is better than 220 MHz, and amplitude noise is less than 0.5%.