We characterize several configurations of compact, Q-switched, 1.5 um lasers based on Er/Yb doped glass. Such lasers are required for eye-safe laser range-finders (LRF), laser markers, and illuminators for 3D and gated imaging. While 1-3 Hz pulse repetition frequency (PRF) is adequate for LRFs, the other applications require much higher PRFs to achieve near-real-time image refresh rates. Lasers described here utilize Er/Yb glass active elements, side-pumped by a 940 nm laser diode bar, or end-pumped by a fiber-coupled laser diode, and made use of active or passive Q-switching (PQS) techniques. Active Qswitching is implemented with resonant scanning mirror, and PQS utilizes Co:Spinel saturable absorbers. Q-switched pulse energies of 5mJ and 3mJ are achieved with side-pumping and end-pumping, respectively. An optical efficiency of over 3.7%, the highest to our knowledge for a PQS Er/Yb glass laser, is measured for the end-pumped implementation. When configured to generate 1mJ, the endpumped PQS laser operates over a 2-25 Hz PRF range, with nearly constant pulse energy and optical efficiency. Features and advantages of the various laser configurations are compared.
We describe mid-IR sources utilizing ZGP and CSP Optical Parametric Oscillators (OPO) directly pumped by high efficiency 1.94 μm Tm:YAP Q-switched lasers. Compact Q-switched Tm:YAP lasers, implemented using Cr:ZnS saturable absorbers, generated 29 kW peak power pulses and an average power of 4W. The OPOs, constructed using the latest generation ZGP and CSP crystals with low 1.94 μm absorption, were operated at near-degeneracy with mid-IR output in the 3.6-4.2 μm range. Various doubly-resonant OPO configurations were evaluated, including single-pass pump pass and double-pass pumping. Maximum mid-IR powers of 2.3 W and 2.5 W and optical conversion efficiencies of 58% and 64% were measured for ZGP and CSP double-pass pump OPOs, respectively.
We describe generation of near-infrared (944nm, 970nm), blue (472nm, 485nm), and UV (236 nm) light by frequency up-conversion of 2 μm output of a compact and efficient passively Q-switched Tm:YAP laser. The Tm:YAP laser source was near diffraction limited with maximum Q-switched pulse peak power of 190 kW. For second harmonic generation (SHG) of NIR, both periodically poled lithium niobate (PPLN) and lithium tri-borate (LBO) were evaluated, with 58% conversion efficiency and 3.1 W of 970 nm power achieved with PPLN. The PPLN 970nm emission was frequency doubled in 20mm long type I LBO, generating 1.1 W at 485nm with a conversion efficiency of 34%. With LBO used for frequency doubling of 2.3 W of 1888 nm Tm:YAP output to 944nm, 860mW was generated, with 37% conversion efficiency. Using a second LBO crystal to generate the 4th harmonic, 545mW of 472nm power was generated, corresponding to 64% conversion efficiency. To generate the 8th harmonic of Tm:YAP laser emission, the 472nm output of the second LBO was frequency doubled in a 7mm long BBO crystal, generating 110 mW at 236nm, corresponding to 21% conversion efficiency.