A diode-end-pumped Tm:YLF laser, passively Q-switched (PQS) with a Cr:ZnS saturable absorber, generated 10 mJ, 29 ns-long pulses at 1.9 μm, corresponding to a peak power of 350kW. A PQS laser operated at a maximum pulse repetition frequency (PRF) of 1 kHz, generating an average power of 10 W. The demonstrated pulse energy and average power represent significant increases over previous results with PQS Tm-doped lasers, and the 10 mJ pulse energy is comparable to that of much more complex actively Q-switched versions of such lasers. Using a cadmium silicon phosphide (CSP) optical parametric oscillator (OPO), the laser output was converted to 3.5-4.2 μm mid-IR emission. The OPO exhibited an optical efficiency of 64%, and generated 6W of mid-IR power.
Highly efficient, diode pumped Tm:YAP lasers generating emission in the 1.85-1.94 μm range are demonstrated and characterized. Laser optical efficiencies of 51% and 45%, and electrical efficiencies of 31% and 25% are achieved under CW and Q-switched operation, respectively. Laser performance was characterized for maximum average powers up to 20W with various cavity configurations, all using an intra-cavity lens to compensate for thermal lensing in the Tm:YAP crystal. Q-switched lasers incorportating a Cr:ZnS saturable absorber (SA), resonant mechanical mirror scanner, or acousto-optic modulator were characterized. To enable higher average output powers, measurements of the thermal lens were conducted for the Tm:YAP crystal as a function of pump power and were compared to values predicted by a finiteelement- analysis (FEA) thermal-optical model of the Tm:YAP crystal. A resonator model is developed to incorporate this calculated thermal lens and its effect on laser performance. This paper will address approaches for improving the performance of Tm:YAP lasers, and means for achieving increased average output powers while maintaining high optical efficiency for both SA and mechanical Q-switching.
We describe and compare the performance of two types of compact, passively Q-switched Yb:YAG 1030nm lasers and their use for 257nm fourth harmonic generation (FHG). In the first implementation, an end-pumped Yb:YAG laser produced a 250μJ pulse train with an average power at 1030nm of 3.6W. Using a 10mm LBO crystal (70% doubling efficiency), followed by a 7mm BBO crystal (45% conversion efficiency), 1.1W at 257nm was generated (overall FHG efficiency of 30%). The second implementation was a side-pumped Q-switched Yb:YAG laser pumped by a 200W diode bar. A 10mm KTP crystal followed by a 6mm BBO crystal resulted a 15% FHG conversion efficiency. The UV emission was in a form of 1-5 Hz PRF, 2ms long burst of 0.2mJ pulses with a 30kHz intra-burst PRF. Within a 1.65ms emission window, an 11.5mJ burst at 257 nm was generated that had a maximum intra-burst power of 7W. This paper will address the merits of each approach for realizing a man-portable laser suitable for ultraviolet Raman explosives detection.
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