Abstract

A quantitative approach for calculating the noise due to the stochastic nature of multimode laser radiation in nonlinear-optical processes is presented. The model is applicable when it is appropriate to describe the nonlinear interaction with a perturbation expansion in the incoming field, and it is derived under the assumption of independent individual laser-mode intensities and phases. It is possible to separate noise contributions from mode-amplitude and -phase fluctuations, respectively, and also to identify the noise contribution from each laser source. For coherent anti-Stokes Raman scattering (CARS) thermometry, the model shows that with a single-mode pump laser the stochastic phases in the dye laser do not generate noise in the conventional approach and that amplitude fluctuations in the dye laser(s) do not (significantly) generate noise in the dual-broadband approaches. Thus, in the dual-broadband approaches, the spectral noise in the Stokes beam is not a lower limit for the noise in the CARS beam. The model seems to overestimate the noise due to phase fluctuations and to underestimate the noise due to amplitude fluctuations.

© 1988 Optical Society of America

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