Coherent versus incoherent eyesafe lidar detection at 2.09 μm

A 2 μm laser radar has been built to compare coherent and incoherent detection schemes. The 2 μm wavelength is of interest for its high atmospheric transmission and because it is eye safe. This 2 μm system is capable of either a coherent or an incoherent mode, is tunable in a small region around 2 μm, and will be used to look at the statistical nature of the laser radar return pulse for typical targets. The targets of consideration are glint and speckle targets. An analysis of the noise sources inherent in the system has been done and the magnitude of these noise sources has been determined. The probability density functions for both glint and speckle targets for both coherent and incoherent detection arrangements were identified. Knowing the probability density functions for each case, the probability of detection was calculated. Experimental data are compared to the theoretical probability density functions. A description of the laser radar setup along with the theoretical expectations of the system is presented