DWIGHT 0. NORTH?, FELLOW, IEEE Summary-The smallest signal discernible through background noise is formulated in terms of the pdse energy, its repetition rate, the receiver design, and the choice of integrating and indicating means.The smallest signal visible on a Type-A scan can be improved upon by the use of electromechanical integrators. Integration before detection is, in theory, ultimately the most effective, but runs into serious practical difficulties. These are avoided when the integration is performed after detection.Optimum predetector selectivity is formulated. The optimum detector (square law) is found, and other detectors compared. A transmitter criterion provides a basis for comparing the effectiveness of transmitters, and shows how, at the expense of range resolution, longer pulses can increase visibility. I. ELEMENTS OF THE PROBLEMK H I N "TARGET" lying within a segment of range Ar reflects a pulsed carrier, producing a t the terminals of a receiving antenna an opencircuit voltage, e(t) = F ( t ) COS (00t + e).(1)With a few exceptions, the pulsing function will be supposed rectangular, duration r , and recurrent, period T , so that in a sample period, -T / 2

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A comprehensive model of the injection laser: Formulation and test of the current dependence of spontaneous and coherent emission A proposed relation between spontaneous and coherent properties of injection lasers is applied to several published results. On experimental and theoretical grounds it is shown that the parameter 1 + X, the ratio of conventional gain coefficient to prorated loss for the strongest cavity mode, can be determined from the spontaneous emission. Over a limited range above unity, 1 + X is the ratio of spontaneous intensity at the operating point to its value at threshold. This supplies a needed experimental connection between spontaneous studies at frequencies higher than the lasing band and the coherent properties. Published data of the current dependence of spontaneous emission are discussed in this framework, and the information needed to intercompare their internal state is pointed out. In general, fundamental differences in laser dynamics should be evidenced by radically different values of the critical parameter P * of the nonlinearity associated with the power dependence of X. All published values of p* are of order 5 mW per cavity mode, as predicted, indicating a similarity in the nonlinearity for quite different types of material. The recent observation that P * is independent of facet area gives strong support to the idea that the source of the nonlinearity is saturable optical absorption in a strongly interacting system.

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