Absorption and the dimensionless overlap integral for two-photon excitation

The interaction of an absorption line and a resonant laser is often modeled using a spectral overlap integral. Previous investigators have modified th e traditional overlap integral to obtain a dimensionless overlay integral t hat affords a more practical interpretation. Unique to the derivation of th e modified integral is the treatment of the laser-spectral-irradiance profi le - its area is normalized to equal the spectral full-width at half-maximu m. In this paper, the modified laser spectral irradiance is applied to obta in a dimensionless overlay integral for multi-photon absorption, including the case of two-photon absorption. Close attention is given to the units ap plied to the calculation of absorption rate coefficients, including those f or the laser flux, laser irradiance, interaction cross sections, and distri bution functions. The results are tabulated for two cases - frequency expre ssed in units of wave numbers and frequency expressed in units of Hertz. (C ) 2001 Elsevier Science Ltd. All rights reserved.