Photon-trapping effects

In Fig. 14, we plot the correlation functions (146) and (147) computed from the equations of motion (96) for the case of degenerate transitions (A = 0) and two different values of p p = 0 corresponding to the case of perpendicular dipole moments, and p = 0.99 corresponds to almost parallel dipole moments. We have chosen p < 1 to avoid population trapping, which can appear for p = 1. The correlations show the characteristic photon antibunching effect [59] that g1-11 (x)... 

Katori, H., Ido, T., Isoya, Y., and Kuwata-Gonokami, M. (1999). Magneto-optical trapping and cooling of strontium atoms down to the photon recoil effect. Physical Review Letters, 82, 1116-1119. 

Compared with the momentum of impinging atoms or ions, we may safely neglect the momentum transferred by the absorbed photons and thus we can neglect direct knock-on effects in photochemistry. The strong interaction between photons and the electronic system of the crystal leads to an excitation of the electrons by photon absorption as the primary effect. This excitation causes either the formation of a localized exciton or an (e +h ) defect pair. Non-localized electron defects can be described by planar waves which may be scattered, trapped, etc. Their behavior has been explained with the electron theory of solids [A.H. Wilson (1953)]. Electrons which are trapped by their interaction with impurities or which are self-trapped by interaction with phonons may be localized for a long time (in terms of the reciprocal Debye frequency) before they leave their potential minimum in a hopping type of process activated by thermal fluctuations. 

At low density (< 1012 cm-3) and temperatures > 100 /jK the two-photon lineshape is a double exponential, exp(- p /<5p0) [3], as expected for Doppler-free two-photon excitation by a Gaussian laser beam of a thermal gas [29]. Here v is the laser detuning from resonance and 8v0 is the linewidth due to the finite interaction time of the atom with the laser beam. At low temperature, lines as narrow as 3 kHz (FWHM at 243 nm) have been observed. A detailed discussion of this lineshape in the trap and the appearance of sidebands due to coherence effects for repeated crossing of the laser beam can be found in [30]. 

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