Comparison of atmospheric laser propagation between the NIR and MWIR

We report results from field experiments that have compared laser propagation in the near infrared (NIR) and mid-wave infrared (MWIR) in a variety of atmospheric conditions. Single frequency laser sources at 1.565 mu m and 3.603 mu m were transmitted through a single common aperture telescope to ensure that each beam was affected by nearly identical turbulence. Tests were performed on a one-way, 1.26 km path over land and on a round-trip, 2 x 1.41 km path that was mostly over water using a broadband retro-reflector. It is expected from theory that scattering and turbulence should have relatively less effect at longer wavelength, however quantitative measurements in real world conditions are important because of the complexity and simplifying assumptions required in the theory. Although communication and laser radar systems that operate in the NIR at similar to 1.5 mu m benefit from well-developed sources and detectors, it is expected that propagation in the MWIR can offer a significant advantage. The objective of this work was to quantify the relative propagation effects under realistic conditions.