Understanding CREIL and ISRS Interactions in Light-Matter Dynamics

1. The Coherent Raman Effect on Incoherent Light. The spectrum of the “accreting neutron stars”. Jacques.MORET-BAILLY@u-bourgogne.fr

2. In a parametric light-matterinteraction : 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. 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 Recall of refraction (Huygens)

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 0 • Energies of the eigen-levels of the setof refracting molecules Eigen-level of polarisation Absorption Stimulated emission Initial eigen-level • Time

6. Simultaneous refraction of two beams Eigen energies of the set of molecules CREIL interaction Ground state 0 Beams of increasing intensities 0

7. 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 0 Beams of increasing intensities 0

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, 99 1971). 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 .