Abstract

Bragg diffraction from volume thermal gratings excited by crossed Gaussian laser beams provides a sensitive measurement of one- and two-photon absorption in fluid solution. The minimum detectable one-photon absorptivity (base e) was α_min = 1.0 × 10⁻⁶ cm⁻¹ in a 3.3-nL probed volume, corresponding to the detection of 5 × 10⁻¹⁹ cm². The two-photon cross section of benzene at 532 was determined by this technique to be 1.5 × 10⁻⁵¹ cm⁴ sec; detection of benzene two-photon absorption could be accomplished at concentrations as low as 6.4 × 10⁻⁴M. The method produces a diffracted signal on a zero background, so that detection of nonradiative relaxation of the sample is limited only by shot noise.

© 1985 Optical Society of America

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