Liquid Three Photon Fluorescence

Abstract

STUDIES of the blue fluorescence generated in solutions of certain organic dyes, for example, cryptocyanine, by the intense emission of a Q-switched ruby laser have demonstrated the two photon nature of the excitation process1,2. A similar fluorescence effect is observed in the pure solvent 1-chloro-naphthalene (CLNP) and attributed to two photon absorption in the tail of the strong band centred near 300 nm1,2. This intensity-dependent absorption is also thought to initiate the strong self-Q-switching effect observed when a cell containing the pure solvent is inserted in the cavity of a ruby laser3. There is no a priori reason to exclude higher order excitation processes if the incident light has the appropriate wavelength and so we have looked for the characteristic fluorescence of CLNP using a mode locked neodymium laser as the intense light source. The operating wavelength of this laser, 1.06 µm, is such that a positive result would indicate excitation by three photon absorption.