Speckle mitigation for coherent detection employing a wide band signal

Abstract

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 the 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 corresponds to the spacing of peaks in a speckle pattern of an image plane. The use of multiple receiving telescopes having the characteristic dimension allows for independent measurements concurrently by each of the receiving telescopes. The train of illuminating pulses is generated 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 preferably equals the number of independent measurements concurrently attainable during reception of the reflected pulse train. Alternatively, the laser frequency may be linearly swept such that the overall bandwidth is equal to the bandwidth encompassed by the line spectrum of the generated pulse.

Dependencies are inferred from the claim text.