SPECKLE MITIGATION FOR COHERENT DETECTION EMPLOYING A WIDE BAND SIGNAL

摘要

Multiple independent spectral measurements of light reflected from a target are produced concurrently by illuminating the target with a train of laser pulses wherein the train of pulses produces a line spectrum within the illuminating signal. A characteristic dimension of receiving aperture is established based on illuminating wavelength, a cross-sectional dimension of illuminated region of a target, and the range between a target and the receiving aperture or image plane. The characteristic dimension is the spacing of peaks in a speckle pattern of an image plane. The speckle results from destructive and constructive interference of coherent light waves reflected from the target. The use of multiple receiving telescopes having the characteristic dimension, allows for independent measurements concurrently by each of the receiving telescopes. In addition, the generation of a train of pulses of illuminating radiation, or light, by laser is accomplished by mode-locked operation of the laser for synchronization of sinusoidal components at line frequencies of the pulse train spectrum, and wherein the spacing of the spectral lines is at least a decorrelation frequency. The number of spectral lines transmitted within each pulse equals the number of independent measurements attainable concurrently during reception of the reflected pulse train of light. Alternatively, in lieu of the line spectrum, the frequency may be swept linearly during the duration of a pulse such that the overall bandwidth of the frequency sweeping is equal to the bandwidth encompassed by the line spectrum of a pulse.