Spontaneous Emission in the Frequency Up-Conversion Process in Nonlinear Optics

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Abstract
The spontaneous emission in the frequency up-conversion process in nonlinear optics due to the second-order process consisting of the mismatched spontaneous down-conversion process followed by the phase-matched up-conversion process is studied in detail as a quantum-mechanical scattering problem. The calculated integrated intensity of the spontaneous emission within the spectral and angular widths for the first-order phase-matched up-conversion process is found to be exactly the same as that obtained by Smith and Townes classically. By carefully choosing the parameters involved, it may be possible to eliminate the spontaneous emission from the detected output at the sum frequency of the up-conversion process. It therefore appears that the up-conversion process may indeed be made essentially noise-free and, with further improvements in the conversion efficiency, it is a very promising means of detecting low-level infrared radiation.