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 μm and 3.603 μm 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 ~1.5 μm 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.
The U.S. Naval Research Laboratory (NRL) established a one-way Gigabit Ethernet lasercomm link during the
Seahawk exercise in August, 2007 to transfer data ~8 miles across the inlet of San Diego Bay from Point Loma to
the Imperial Beach base camp. The data transferred over the link was from an NRL developed, wide field of view
(90 degrees), high resolution, mid-wave infrared camera operating at 30 frames per second. Details of the high
speed link will be presented as well as packet error rate data and atmospheric propagation data taken during the two
week long exercise.
We report the first demonstration of mid-IR coherent laser radar operation near 3.6 micrometers . In many low altitude environments, the wavelength region from 3.5 - 4 micrometers has advantages for laser beam propagation because the detrimental effects of scattering and turbulence are less severe than at shorter wavelengths. In addition, under conditions of high humidity, water vapor absorption in the mid-IR is also significantly lower compared to the long-IR region at 9-11 micrometers . The source in this work is a 100 mW, frequency stable cw-optical parametric oscillator (OPO) based on periodically poled lithium niobate. The frequency stability of the source is discussed and laboratory heterodyne experiments measuring small Doppler shifts from vibrating targets are described.
A compact and light weight imaging laser radar system is being developed for an advanced exo-atmospheric missile interceptor platform for the Discriminating Interceptor Technology Program (DITP). The laser radar will be used in combination with a two- color passive IR sensor to provide high angular resolution information for long range tracking and discrimination of multiple targets. A direct-detection approach at 532 nm has been chosen to provide the best overall capability in a system which can be fielded in the near term. The laser radar is designed to operate at 25 W for a limited run time and output short 1.3 ns pulses at 100 Hz. A high speed 10 X 10 pixel receiver capable of efficient single photon detection is also being developed.