High-Power High-Beam-Quality 330-nm Laser From a Frequency-Quadrupled Nd:YAG Laser

We demonstrate a high-power high-beam-quality ultraviolet (UV) laser at 330 nm based on fourth-harmonic generation (FHG) of a diode-side-pumped 1319-nm Nd:YAG laser. A 23.2-W Q-switched Nd:YAG laser at 1319 nm with beam quality factor
$M^{2}=1.15$
and optical to optical conversion efficiency of 6.5% was employed as the fundamental wave source. First, the output at 1319 nm was frequency doubled to 660 nm in an LiB
₃
O
₅
(LBO) crystal with an average output power of 11.3 W. Then, it was frequency doubled again in another LBO crystal to obtain the FHG output at 330 nm. The maximum average output power at 330 nm was up to 7 W, and the beam quality factor
$M^{2}$
was measured to be 1.45. The conversion efficiency was 48.7% at the first second-harmonic generation (SHG) stage, and the conversion efficiency of the second SHG stage was 61.9%, corresponding to a total conversion efficiency from infrared to UV of 30.2%. To the best of our knowledge, this is the first 330-nm UV source generation from a diode-side-pumped frequency-quadrupled 1319-nm Nd:YAG laser.