Propagation of light in low pressure ionised and atomic hydrogen. Application to astrophysics

Abstract

The "Impulsive Stimulated Raman Scattering" (ISRS) performed using ultrashort laser pulses shifts the light frequencies. Tried using ordinary incoherent light, it keeps its qualitative properties except the nonlinearity due to the power of the laser pulses. The relative frequency shifts of the "Coherent Raman Effect on Incoherent Light" (CREIL) which is obtained do not depend on the intensity and, in a first approximation, on the frequency of the light. As CREIL does not blur the images and the spectra, its shifts may be confused with Doppler shifts. ISRS and CREIL are parametric effects which do not excite the matter, transferring energy from hot beams to cold beams; for CREIL, the cold light is thermal radiation which is heated. CREIL requires low pressure gases acting as catalysts. These gases must have Raman transitions in the radiofrequencies range: for instance H2+ or excited atomic hydrogen in a magnetic field. The spectral lines resulting from a simultaneous absorption (or emission) and CREIL have a width at least equal to the frequency shift, so that the lines of a complex spectrum may be weakened and mixed, becoming nearly invisible. In astrophysics, molecular hydrogen is ionised, but so quickly destroyed by collisions that it persists only at pressures low enough to provide CREIL: Thus it is invisible. It contributes to the "cosmological redshift" and to an amplification of the 2.7K radiation. Using CREIL, the interpretation of the spectra of the quasars requires only usual laws of physics, usual matter and usual astronomical objects: a star, an accretion disk, satellites in a plasma of atomic hydrogen.