Holographic Wavefront Correction for SHADOE LIDAR Receivers, Phase I

Current shared aperture diffractive optical elements (SHADOE) have intrinsic residual wavefront errors on the order of 20 waves which limits the angular resolution of the LIDAR application to a range between 150 and 400 micro-radians. It is possible to reduce these aberrations by constructing a secondary holographic correction plate using the aberrated wave from the SHADOE as one of the two construction waves. The other construction wave is either a collimated wave or an f#2 focused wave. All five overlapping apertures require individually constructed plates. This method of correction requires the use of the final playback wavelength for construction and so is useful for 532 and 355nm but not for 1064 nm. Computed diffractive optics can be used for 1064 nm using measured aberrations at the same wavelength. This proposal deals just with fabrication and test of the 355 nm LIDAR applications for which an entirely optical recording set up is adequate. Correction plates in the 2 inch diameter range are proposed with likely reduction in angular spread to under 50 micro-radians, which will greatly improve the signal to noise numbers in a LIDAR application. More »