Narrow linewidth UV sources at 257nm

摘要

We describe and compare the performance of two types of compact, passively Q-switched Yb:YAG 1030nm lasers and their use for 257nm fourth harmonic generation (FHG). In the first implementation, an end-pumped Yb:YAG laser produced a 250μJ pulse train with an average power at 1030nm of 3.6W. Using a 10mm LBO crystal (70% doubling efficiency), followed by a 7mm BBO crystal (45% conversion efficiency), 1.1W at 257nm was generated (overall FHG efficiency of 30%). The second implementation was a side-pumped Q-switched Yb:YAG laser pumped by a 200W diode bar. A 10mm KTP crystal followed by a 6mm BBO crystal resulted a 15% FHG conversion efficiency. The UV emission was in a form of 1-5 Hz PRF, 2ms long burst of 0.2mJ pulses with a 30kHz intra-burst PRF. Within a 1.65ms emission window, an 11.5mJ burst at 257 nm was generated that had a maximum intra-burst power of 7W. This paper will address the merits of each approach for realizing a man-portable laser suitable for ultraviolet Raman explosives detection.