Recent advances in efficient long-life, eye-safe solid state and CO2 lasers for laser radar applications

There is increasing interest in the comparative roles of CO 2 and the more recently developed eye-safe solid-state lasers for long-life efficient laser radar applications. This paper assesses recent technology advances in each area and their roles in laser radar and especially Doppler lidar and DIAL development. The key problems in eye-safe solid-state lasers are discussed relating to the energy transfer mechanisms between the complicated energy level manifolds of the Tm,Ho,Er ion dopants in hosts with decreasing crystal fields such as YAG or YLF. One concerns optimization of energy transfer for efficient lasing through choice of dopant concentration, power density, crystal field and temperature, with the highly practical goal of minimal cooling needs. Another key problem, specific to laser radar and lidar, involves tailoring of energy transfer times to provide efficient energy extraction for short, e.g., Q-switched pulses used in DIAL and Dopper lidar. Special emphasis is given to eye-safe lasers in the 2 μm range because of the high efficiency applications to DIAL and (windshear) Doppler lidar and because they are well suited for Optical Parametric Oscillator frequency conversion into the important ≈ 4 to 5 μm DIAL range. The discussion of CO 2 lasers concerns recent advances in Pt/Sn0 2 oxide catalysts and other noble metal/metal oxide combinations. Emphasis is given to the dramatic effects of small quantities of H 2 0 vapor for increasing the activity and lifetime of Pt/Sn0 2 catalysts and to increased lifetime operation with rare isotope 12 C 18 O 2 lasing mixtures; iL-the 12 C 18 O 2 laser wavelengths in the 9.1 μm range are of special interest for space-based Doppler lidar such as the proposed Laser Atmospheric Wind Sounder.