The fundamental characteristics of heterodyne and nonheterodyne imaging laser radars are presented in terms of information content, structual complexity, and sensitivity limits. The sensitivity characteristics of heterodyne and nonheterodyne laser receivers are quantitatively compared. When feedback amplification or lowhyphen;noise multiplication gain is available in the receivers, the direct detection of laser signals can approach or even surpass the sensitivity or coherent detection. The concept of lsquo;lsquo;selfhyphen;homodynersquo;rsquo; is introduced and its potential application to laser radar measurements is addressed.
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