Propagation of light in low-pressure ionized and atomic hydrogen: application to astrophysics

Impulsive stimulated Raman scattering (ISRS) uses ultrashort laser pulses to shift light frequencies; the frequency shift depends on the power of the laser pulses because this power is very large. The relative frequency shifts of coherent Raman effect on incoherent light (CREIL) described in this paper are independent on the intensity of the ordinary incoherent light that it uses, and, in a first approximation, on the frequency of the light. Since CREIL does not blur images or alter the spectral pattern, CREIL effect may be confused with Doppler frequency shifts. ISRS and CREIL are parametric effects that do not excite matter; they transfer energy from "hot beams" to "cold beams." These transfers correspond to spectral shifts; in CREIL thermal radiation is blue-shifted, that is heated. CREIL requires low-pressure gases acting as catalysts. These gases must have Raman transitions in the radio frequencies range: for example, 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 interstellar space, molecular hydrogen is ionized, but since H₂⁺ is quickly destroyed by collisions it persists only at pressures low enough to provide CREIL; the redshift widens the weak absorption lines of H₂⁺ which becomes undetectable. It contributes to the "cosmological redshift" and amplification of the microwave 2.7 K background radiation. Using only well-established physics and normal astronomical objects, CREIL provides a plausible explanation for the enigmatic spectra of the quasars.