Use of diverging and nonmonochromatic pump waves in nonlinear spectroscopy of infrared radiation

An analysis is made of the possibility of using nonlinear optics methods in the visualization of infrared radiation in nonlinear spectroscopy. Various nonlinear infrared spectrometers based on this approach are classified. A detailed theoretical study is made of an "integrating" nonlinear spectrometer in which the integrated intensity of the converted visible radiation is measured. This intensity is proportional to the spectral density of the infrared radiation intensity averaged within the limits of the phase-matching band. An investigation is made of the spectral resolution, light transmission, and other characteristics of a nonlinear spectrometer. The influence of the nonmonochromaticity of the pump radiation and of the spatial divergence of the interacting waves is considered. A similar analysis is also made of the "local" nonlinear spectrometer in which the converted radiation is analyzed by a visible-light spectrometer. The results of the general theory are illustrated by calculations performed for specific nonlinear crystals.