Time-delay Fizeau phase-conjugate interferometer

Photon-echo novelty filter: a unique time-differential sensor of optical wave-front distortion caused by airborne turbulence

To continue our earlier research on the photon-echo novelty filter, we lengthen the novelty filter's response time by 3 orders of magnitude from nanoseconds to microseconds. On the microsecond time scale of airborne turbulence we demonstrate the potential of the novelty filter as a unique time-differential phase sensor. We observe no considerable degradation of the filter's sensitivity and accuracy to as high as 50 and 200 micros, respectively. This result demonstrates that the filter can be continuously tuned with regard to its response time over a wide range. We further apply the novelty filter to the probing of phase distortions of a laser beam going through a He jet. We also investigate issues regarding the operation of the novelty filter to deal with random and spatially nonuniform phase distortion. The relation of the photon-echo novelty filter to traditional double-exposure holography and the role of the time-differential sensor in adaptive optics are discussed.