Narrow Linewidth 177.3-nm Nanosecond Laser With High Efficiency and High Power

We demonstrate a high-efficiency high average power vacuum ultraviolet (VUV) 177.3-nm laser with a narrow linewidth generated by second harmonic (SH) generation from a nanosecond (ns) 355-nm laser in the
${\rm KBe}_{2}{\rm BO}_{3}{\rm F}_{2}$
crystal. The 355-nm pumping source was a frequency-tripled
$Q$
-switched 1064-nm Nd:YAG oscillator–amplifier laser system, in which a quartz etalon was used to compress the linewidth of 1064-nm laser. Under a pump power of 5.2 W at 355 nm with a linewidth of 2 pm, a high average power of 146.5 mW at 177.3 nm with a linewidth of
${\sim}{\rm 0.71}~{\rm pm}$
was obtained, corresponding to an SH conversion efficiency as high as 2.8%. This is, to the best of our knowledge, the highest output power and highest SH conversion efficiency for the ns 177.3-nm lasers. This VUV coherent light can be used as light source for fine precision spectroscopy and semiconductor photolithography owing to its narrow linewidth, high energy resolution, and high average power.