Experimental Research Of The Fourth Harmonic265.6nm CW Lasers

Narrow-linewidth continuous-wavelength(CW) lasers in the ultraviolet(UV) band have very important applications in the fields of UV precision spectroscopy and mercury optical clock. The output of lasers in the infrared or visible band is usually frequency-doubled to get radiation in the UV band due to the limitations of direct laser output in UV band. In this thesis, we will introduce the experimental system for the UV laser at265.6nm, which was built by frequency doubling the infrared output of a1062ran fiber laser twice. The experimental system contains frequency doubling the1062nm output of a fiber laser by single-passing a PPLN (Periodically Poled Lithium Niobate) crystal, generating the radiation at531nm, and intracavity frequency doubling the531nm green light with a BBO(P-BaB2O4) crystal, generating UV light at265.6nm.In the1062nm-531nm system, the scheme for frequency doubling was designed based on the properties of the nonlinear optical crystal PPLN. The temperature tuning curve of the PPLN crystal was measured and the data was fit to know the optimum operating temperature, which was found to be48.5℃. and the normalized conversion efficiency under this temperature is44.65%/W。In the531nm-265.6nm experimental system, considering the focus factor and the stability conditions of ring cavity, the selection of the length and waist of the ring cavity was detailed discussed, and two kinds of ring cavities was designed for the Brewster angle cut and non-Brewster angle cut BBO crystals respectively. The theoretical normalized single-pass conversion efficiency of the BBO crystal was estimated to be0.0114%/W。 Based on the theoretical results, an integrated ring cavity was manufactured and its resonance frequency was locked to the frequency of the531nm fundamental light by using the dither locking scheme. The stability of the resonance frequency was estimated to be about4.6X10-12and a weak265.6nm UV output was obtained in this condition. By comparing the experimental data of the second frequency doubling stage with theoretical results, the possible reasons for the low conversion efficiency of the ring cavity were discussed and some suggestions for optimizations were also given.