1. The Coherent Raman Effect on Incoherent Light.
The spectrum of the “accreting neutron stars”.

2. No quantification of the energy of the light.
In a parametric light-matter interaction :
The matter is polarized during the light pulses, then it returns to the initial stationary state. Therefore the matter may be considered as a catalyst.
All identical molecules get the same polarization : if there are enough identical molecules, the interaction is coherent, it produces well defined wave surfaces, light beams.
While a single photon is refracted, each molecule of a prism absorbs an infinitesimal part of the energy h :
No quantification of the energy of the light.

3. Examples of parametric interactions
With a single beam : Its energy, therefore its frequency cannot be changed : refraction.
With several beams energy may be transferred. To follow
thermodynamics, the beams having a high Planck's temperature leave energy, are redshifted. It is CREIL or ISRS, frequency doubling ...
( A lot of experiments using laser or microwave sources)
CREIL or ISRS

4. Recall of refraction (Huygens)
Incident waves
Envelope of the wavelets, identical to an incident wave, but late of p /2
Molecule
Wavelets emitted by the molecules
The incident and scattered waves interfere into a single, late wave
Retrograde wave cancelled by the volume emission

5. Splitting by the polarisation
Refraction of a pulse of light by a set of N identical molecules
The degeneracy of the set of molecules is the product of N by the degeneracy of the molecular eigen-level. The eigen-level of the set is split by the polarisation.
Intensity of light
Energies of the eigen-levels of the set of refracting molecules
Eigen-level of polarisation
Absorption
Stimulated emission
Splitting by the polarisation
Initial eigen-level
Time

6. Simultaneous refraction of two beams
Eigen energies of the set of molecules
CREIL
interaction
Ground state
Beams of increasing intensities

7. CREIL allowed Quadrupolar interaction (Resonant Raman)
Simultaneous refraction of two beams :
The states of polarisation have the same parity : An intermediate level is necessary for a dipolar interaction
Eigen energies of the set of molecules
CREIL allowed Quadrupolar interaction (Resonant Raman)
CREIL
interaction
forbidden
Ground state
Beams of increasing intensities

8. CREIL and ISRS obey the same theory, but:
CREIL uses the long, low peak energy of the pulses making the ordinary incoherent light;
ISRS uses ultrashort, high peak energy laser pulses.
Properties of the catalyst :
Chemically identical molecules remain identical during the pulses if the pulses are ultrashort that is “shorter than all relevant time constants” (Lamb, Rev. Mod. Phys. 43, ). The relevant time constant are:
The collisional time
The period of the quadrupoles which allow the interaction.

9. Gases allowing the CREIL :
Must have a resonance in the megahertz range :
All gases with a convenient Zeeman or Stark effect.
Gases having a genuine or accidental hyperfine structure,
in particular heavy atoms and molecules.
In particular :
- atomic hydrogen in the n=2 state : 178 MHz, 59 MHz and 24 MHz with F=1. (For n=1, the 1420 MHz frequency is too high; for n>2 frequencies and CREIL are low).
- some neutral or ionized compounds of H and D .