Showing papers by "Jeffrey H. Shapiro published in 1986"

Performance Analyses For Peak-Detecting Laser Radars

Abstract: In 2-D pulsed imager and 2-D Doppler imager laser radars, the intermediate frequency return signals are generally filtered, envelope detected, and peak detected in a pre-processor sub-system. Because the input to the peak detector is often thresholded, these systems are subject to dropouts. Because laser radar targets commonly exhibit speckle statistics, these systems are prone to detecting anomalous peaks. This paper presents results for the dropout, anomaly, and accuracy performance of peak detection pre-processors. The impact of the pre-processor on reflectivity determination is also analyzed. The essential features of the theory are verified through peak-detector reflectivity measurements made with the MIT Lincoln Laboratory 2-D pulsed imager laser radar test bed.

Semiclassical theory of light detection in the presence of feedback

Abstract: The usual formulations of the quantum and semiclassical theories of photodetection presume open-loop configurations, i.e., that there are no feedback paths leading from the output of the photodetector to the light beam impinging on that detector. In such configurations, the qualitative and quantitative distinctions between the quantum and semiclassical theories are well understood. In the quantum theory, photocurrent and photocount randomness arises from the quantum noise in the illumination beam, whereas in the semiclassical theory the fundamental source of randomness is associated with the excitations of the atoms forming the detector. Nevertheless, the quantum theory subsumes the semiclassical theory in a natural way.1

Vector-field quantum model of degenerate four-wave mixing

Abstract: A quantum theory of degenerate four-wave mixing is presented in which the atomic medium consists of stationary four-level atoms, each with three degenerate excited states, and the interacting light beams are allowed to be in different states of polarization. This vector-field theory differs from the scalar-field theory of Reid and Walls [Phys. Rev. A 31, 1622 (1985)] in that there are new atomic variables in the Langevin equations which are related to the induced coherence between the upper atomic states. It is found, for the assumed set of atomic levels, that this seemingly different mechanism of four-wave-mixing gain does not circumvent the degrading effect of spontaneous emission on squeezing obtainable via degenerate four-wave mixing. The theory is applied to both forward and backward degenerate four-wave mixing with nearly collinear geometry, and specialized to the case in which the polarization states of the two pump modes are mutually orthogonal. It is found that for both forward and backward configurations, the range of pump intensity for which squeezing can be achieved in the vector-field case is larger than that in the scalar-field case, and the maximum amount of squeezing obtainable at a particular pump detuning is comparable in both cases.