355-nm UV Generation by Intracavity Frequency Tripled Passively $Q$-Switched Nd:YAG/Cr$^{4+}$:YAG Laser

In this letter, intracavity frequency-tripling of a diode-end-pumped passively
Q
-switched Nd:YAG/Cr
⁴⁺
:YAG composite laser has been demonstrated for the first time. Under the absorbed pump power of 7.2 W, the maximum UV output power of 110 mW is obtained with the beam quality parameter
M
²
of 2.95. The minimum pulsewidth and the highest repetition rate are 23.9 ns and 19.6 kHz, respectively. The corresponding single pulse energy and pulse peak power are 5.6 μJ and 0.23 kW. The fluctuation of the average output power at 110 mW within an hour operation is tested and determined to be 4.7%.