Absolute Measurement of Two-Photon Cross Sections

Abstract

A method is presented which yields two-photon cross-section values $\delta$ which are independent of the statistical properties of the light beam. A two-cell arrangement is used in which the fluorescence intensity produced by two-photon absorption of a laser beam is compared to that due to one-photon absorption of the harmonic light generated by the same beam in a quartz slab at the top of a Maker fringe. The measurement does not require a calibration of the detecting channels but relies on the knowledge of the one-photon cross section at the harmonic frequency and of the appropriate component of the nonlinear susceptibility tensor ${\chi }^{\mathrm{}\left(2\right)\mathrm{}}$. Values of $\delta$ ($\lambda =6943\mathrm{}$ Å) are presented for several organic molecules and compared to those obtained by other methods.