All Solid-State High-Efficiency Tunable UV Source for Airborne or Satellite-Based Ozone DIAL Systems

Abstract

We designed, built, and tested two laboratory prototype nanosecond UV sources for airborne or satellite-based ozone differential absorption lidar (DIAL) remote-sensing systems. Our prototypes use a 532-nm second-harmonic pulse from a Q-switched injection-seeded Nd:YAG laser to pump an optical parametric oscillator (OPO) that generates a tunable signal wavelength near 803 nm. The OPO signal is mixed with additional 532 nm light either inside the OPO cavity, or in a subsequent sum-frequency generation (SFG) stage, to generate 10-ns pulses at 320-nm. Our system designs result from an integrated, iterative approach where operating parameters including the pump-beam's spatial profile, the second harmonic generation efficiency, the OPO's cavity geometry, output coupling, crystal lengths, and the length of the SFG crystals, are all determined from numerical modeling. By using this approach, we obtained 320 nm pulse energies approaching 200 mJ with overall optical conversion efficiency-from 1064 to 320 nm-exceeding 20%. To optimize efficiency, we incorporate three important design characteristics: a pump beam having a high-quality flat-topped spatial profile, an image-rotating non-planar ring-cavity OPO capable of generating high-quality large-diameter flat-topped beams, and pulse injection seeding of the OPO to achieve near-zero cavity buildup time to enhance the efficiency of sum-frequency mining. We believe additional optimization of our designs may eventually yield UV pulse energies approaching 300 mJ with optical conversion efficiencies comparable to those of our current systems.