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Cohen, S. C.

Publications and source records attributed to Cohen, S. C..

45 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Source self-mixing in the detection of extended incoherent sources

We consider the self-beating of incoherent light from an extended source at a wideband photomixer. The intermediate frequency mean squared current is found to be proportional to the product of the direct detected source power and the power within the IF bandpass about the optical frequency and within the heterodyne field of view. Thus the ratio of the heterodyne signal to self-beating power is proportional to the ratio of local oscillator power to direct detected power. This ratio is usually large for systems employing efficient local oscillators that generate shot-noise-limited operation. In less efficient systems, such as those employing tunable diode lasers, the effects of self-mixing may be significant.

Cohen, S. C.↗
NASA NTRS1974

Semiclassical S-matrix theory of vibrationally inelastic collisions between two diatomic molecules

We derive a semiclassical S matrix for vibrationally inelastic collisions between two diatomic molecules, assuming a collinear geometry. Our theory incorporates a quantum mechanical superposition principle with classical dynamics and, as such, is an extension of the atom-diatomic molecule theory of Miller. The several approximations to the S matrix differ in the complexity with which the interference between various classical trajectories is treated. We report numerical calculations for H2-D2 and D2-D2 collisions based on two different interaction potentials. The cruder approximations yield transition probabilities which agree with exact quantum mechanical results to within a factor of 2. More sophisticated approximations to the S matrix yield excellent quantitative agreement with the quantum calculations.

Cohen, S. C.↗
NASA NTRS1972

Fourier spectrum of beams chopped by circular apertures.

The circular apertures in the case investigated are uniformly spaced. It is assumed that modulation does not alter beam collimation and that diffraction from aperture edges can be neglected. It is also assumed that the diameter of the apertures is equal to the spacing between the trailing edge and the leading edge of successive apertures. The motion of apertures across the beam is rectilinear. Calculations have been performed for both homogeneous and bivariate normal intensity distributions. The absolute values of the first six Fourier coefficients are plotted as a function of the beam radius normalized to aperture radius.

Cohen, S. C.↗
NASA NTRS1972

Photodiodes for ten micrometer laser communication systems

The performance is discussed of 10-micron mercury-cadmiumtelluride and lead-tin-telluride photodiodes in laser heterodyne communication systems. The dependence of detector quantum efficiency, resistance, frequency response, and signal-to-noise ratio on temperature, bias, and local oscillator power are examined. Included in the discussion is an analysis of the feasibility of high temperature operation, and ability of the detector to dissipate power to a heat sink is explored. Some aspects of direct detection response are considered and figures showing flux levels from a blackbody presented.

Cohen, S. C.↗
NASA NTRS1971

N-type mercury-cadmium-telluride photoconductors in optical heterodyne communication systems.

Discussion of the performance of a photoconductive (Hg,Cd)Te detector/mixer in a carbon dioxide laser heterodyne communication system. The utility of computer simulation of the performance of an optical heterodyne detector/mixer is demonstrated. Certain unusual properties of this device are pointed out that, while having a substantial impact on device performance, have received little previous attention.

Cohen, S. C.↗