Two Photon Spectroscopy of Dipole Forbidden Transitions III. Experimental Determination of Two Photon Absorption Spectra Including Polarization Control

Abstract

Abstract A new experimental technique is described which allows the measurement of two‐photon absorption spectra of luminescent molecules and simultaneously the evaluation of the two‐photon polarization parameter Ω over a wide spectral range. The resolution obtained is comparable to conventional UV absorption and polarization spectra. Examples are shown for different types of unsaturated hydrocarbons. The influence of S 1 → S m excitations and of variations of the profile of the exciting laser pulse are discussed. It is shown that careful control of both the quadratic nature of the two‐photon process and the beam profile is essential to avoid artificial features in wide range two‐photon spectra.