Abstract

Of the nonlinear optical techniques, two-photon absorption is certainly one of the more important and useful methods.¹ Two-photon spectroscopy has several advantages over conventional one-photon spectroscopy. In atoms and molecules with a center of symmetry, two-photon spectroscopy can excite states which are not allowed by a one-photon transition. Two-photon spectroscopy can be used to examine bulk properties of a material without interference from surface characteristics. This can be done by the intersection of two laser beams in the material’s Interior. Spectra can be produced that are free of Doppler broadening. Two-photon spectroscopy can easily yield polarization studies of randomly oriented samples. Two photons can be used to probe excited states of much higher energy in atoms and molecules simply because the two photons are not absorbed by the transmitting media (air or window materials), whereas one photon of equal energy is absorbed. Finally, as this study shows, two-photon spectroscopy can utilize a very weak light source (10⁵–10⁶ photons) with nearly unit efficiency and yield useful spectroscopic information.

© 1988 Optical Society of America