Nonlinear optical processes occurring in cold, thin H_2 clouds (assumed densities ~ 10(4) cm(-3) ) located 1-10 pc from O-type stars are considered. For blackbody VUV light from the nearby hot star that is nearly resonant with the Lyman (B -> X) and Werner (C <- X) H_2 absorption lines, elastic scattering is assumed to greatly dominate over inelastic scattering, resulting in the near-resonant VUV flux permeating the entire cloud, with greatly enhanced steady-state flux densities. While one-photon VUV absorptive transitions in the collisionless medium represented by the cloud are highly improbable - essentially because nonconservation of energy would result - the trapped near-resonant VUV light can act to "prime" the cold H_2 molecules so that they can absorb light at visible frequencies - or emit light at infrared frequencies - in simultaneous, energy conserving, two-photon (or Raman) transitions, if visible or IR continuum light is present. In such transitions, the cold H_2 molecules become excited to various singlet-gerade-state quantum levels. We believe that it is from such two-photon absorption processes that the diffuse interstellar bands (DIBs) originate. Two-photon Raman processes are shown to provide enough gain for coherent IR Raman generation (and four-wave parametric oscillation (FWPO)) to occur in the "plane" of the H_2 cloud. This coherent light generation strongly modifies individual intensities of bands in the DIBs spectrum.
American Astronomical Society Meeting Abstracts
- Pub Date:
- December 1996