Detection efficiency of coherent optical radar

Using the Huygens-Fresnel principle, the detection efficiency of a coherent optical radar is formulated. This formulation includes the effect of misalignment between the signal field and the local oscillator field. In the far-field case, the detection efficiency of a diffuse target is approximately half that of a glint target when the transmitter and the receiver are of the same size and the misalignment angle is small. The effect of finite detector size on the detection efficiency is also studied. For a uniform local oscillator field mixed with a signal field at the detector surface, the optimum angular detector size is about twice the wavelength divided by the receiver aperture size. This conclusion is valid for both diffuse and glint targets.