Abstract

Solid-state 2 µm lasers with a high pulse energy and high beam quality are attractive for many applications, such as lidar and medical applications. In addition, using a 2 µm laser as a pump source for chalcogenide laser media doped with divalent transition metal ions, such as Cr:ZnSe and Cr:CdSe, mid-infrared wavelengths exceeding 2 µm can be generated [1]. To obtain a high pulse energy at 2 µm, we selected a Tm:YAG crystal as the laser medium among several laser crystals. Tm:YAG provides both a high energy storage capacity and high pumping efficiency, because of long lifetime (~10 ms) and cross-relaxation between neighboring thulium ions [2]. Tm:YAG also shows lower upconversion losses than Tm,Ho:YAG [3]. However, an output energy exceeding 100 mJ at 2 µm, which is required in several applications, has not been realized owing to the difficulty of avoiding optical damage and ground-state absorption of Tm:YAG. In this study, we report a high pulse energy AO Q-switched Tm:YAG laser pumped with QCW-LD arrays. The maximum output energy of 128 mJ at 2.01 µm was accomplished with a pulse width of 160 ns at room temperature. To the best of our knowledge, this is the highest output energy with nanosecond duration ever reported for a Q-switched solid-state laser with a wavelength of 2.01 µm.

© 2015 IEEE