Comparison of Nd:YVO4-Based Monolithic Microchip Laser Resonators for Single-Frequency Stable, CW Diode-Pumped Laser Sources

Summary form only given. Single-frequency stable, narrow linewidth diode-pumped solid state (DPSS) lasers are commonly used in many applications and science areas, like high-resolution spectroscopy, optical metrology, gravity-wave detection [1], fundamental physics and others. Many of them require optical amplification of the DPSS seed laser to obtain higher output power while maintaining the excellent optical properties of the laser beam (e.g. Coherent Power Summation for military applications). In Ref.[2] the miniature, single-frequency stable DPSS laser operating at 1064 nm and patented structure of the monolithic microchip resonator Nd:YVO₄/YVO₄/YVO₄ were described (Fig.1a). However, from commercial point of view the DPSS seed laser needs to be inexpensive, mechanically and optically stable for wide temperature range, easy to assemble and service. Here, the comparison of the 0.3 mm long a-cut Nd:YVO₄ crystal resonator (Fig. 1b) with dielectric mirrors directly deposited onto the outer crystal surfaces (short resonator-SR) and described in Ref.[3] the 8.5mm long microchip resonator Nd:YVO₄/YVO₄/YVO₄ (long resonator-LR) is presented for the first time. Both resonators were examined in the same DPSS laser module, providing the same conditions for their operation and they were pumped through a 3.5 mm long GRIN-lens collimator (Casix) by a linearly polarized 1W multimode 808 nm laser diode (QA-808-1000-030, Axcel Photonics). In comparison to the LR, the SR configuration provides only 27% less power conversion efficiency (at only 0.3mm resonator/gain crystal thickness) due to back reflection from HR@808nm coating of the pump beam. However, for the 808 nm pump power lower than 250 mW, the SR ensures slightly more output power than LR configuration due to 10-times lower power threshold (Fig. 1c). The pure single longitudinal mode operation was obtained for both configurations (Fig. 1e), nonetheless the SR provides almost 9-times wider temperature range (14-32 °C @ 550mW of pump power) where laser resonator works in single mode (SM) regime (Fig. 1d), than the LR chip (21.2-23.2 °C @ 550mW of pump power). Additionally, the SR configuration does not need a crystals bonding process and it is around 25% cheaper (excluding bonding costs) compared to the LR. Whereas, the output beam divergence becomes around 4-times higher for the SR and it is more sensitive to angular aligning of the pump beam causing that transverse mode distribution can occur. Presented results and comparison were carried out within a commercial TANGO project “Development, optimization and integration of the single frequency seed laser operating at 1064 nm with medium power fiber amplifier”, (TANGO1/266345/NCBR/2015) financed by National Centre for Research and Development (NCBiR), Poland and statutory funds of the Faculty of Electronics (0401/0030/18).