Photon echoes emission

Figure 4. Coherent transients observed in gases and molecular beams. Shown are the photon echo (detected by spontaneous emission), the free induction decay, and Ti for different pressures (iodine gas and beam).

W.P.F. de Ruijter, J.M. Segura, R.J. Cogdell, A.T. Gardiner, S. Oellerich, T.J. Aartsma, Fluorescence-emission spectroscopy of individual LH2 and LH3 complexes Ultrafast Dynamics of Molecules in the Condensed Phase Photon Echoes and Coupled Excitations - A Tribute to Douwe A. Wiersma. Chem. Phys. 341, 320-325 (2007)... 

So the first example of real superradiance was in fact the free induction decay and die decay of the photon echo observed in ruby by Kumit, Abella and Hartmann (1964). When a pulse from a ruby laser was sent onto a ruby crystal, the free induction decay and the echo decay observed were about 50 ns, when compared to the usual Cr " radiative decay time of 4 ms, showing clearly the radiation emission from the macro-dipole. 

Fluorescence line-narrowing and coherent photon-echo techniques (Macfarlane 1992) could give some idea about the homogeneous part of an emission line, but the statistical analysis for the whole sample should still be performed. Supposing only a sensitizer-activator interaction, an average transfer efficiency can be calculated (Dexter 1953). This was studied in some detail by Inokuti and Hirayama (1965). They considered the number of activators located at random in a sphere around a sensitizer in such a way that the activator concentration remains constant when the volume of the sphere and the number... 

Besides various detection mechanisms (e.g. stimulated emission or ionization), there exist moreover numerous possible detection schemes. For example, we may either directly detect the emitted polarization (oc PP, so-called homodyne detection), thus measuring the decay of the electronic coherence via the photon-echo effect, or we may employ a heterodyne detection scheme (oc EP ), thus monitoring the time evolution of the electronic populations In the ground and excited electronic states via resonance Raman and stimulated emission processes. Furthermore, one may use polarization-sensitive detection techniques (transient birefringence and dichroism spectroscopy ), employ frequency-integrated (see, e.g. Ref. 53) or dispersed (see, e.g. Ref. 54) detection of the emission, and use laser fields with definite phase relation. On top of that, there are modern coherent multi-pulse techniques, which combine several of the above mentioned options. For example, phase-locked heterodyne-detected four-pulse photon-echo experiments make it possible to monitor all three time evolutions inherent to the third-order polarization, namely, the electronic coherence decay induced by the pump field, the djmamics of the system occurring after the preparation by the pump, and the electronic coherence decay induced by the probe field. For a theoretical survey of the various spectroscopic detection schemes, see Ref. 10. 

Figure 3 Folded BOXCARS geometry applied in several transient nonlinear optical spectroscopies. In pump-probe spectroscopy, one of the three beams is blocked and the intensity of one of the incoming beams is monitored as a function of the time delay between the remaining two beams (e.g., beam 3 is blocked and beam 2 is monitored as a function of its delay with respect to beam 1, phase-matching condition would be k2 = ki — ki -I- k2>. Beams 4 and 5 are photon echo signals generated from beams 1 and 2. Beams 6 and 7 can be stimulated photon echo or transient grating signals generated from beams 1,2, and 3. In transient grating two of the beams are time coincident. In coherent anti-Stokes Raman spectroscopy, beams 1 and 3 are time coincident and carry the same frequency the difference between this frequency and that of beam 2 (so-called Stokes beam) matches a vibrational frequency of the system and beam 6 will correspond to the anti-Stokes emission.

We have reviewed the EOM-PMA method for the calculation of two-pulse-induced (spontaneous emission, pump-probe, photon echo) and three-pulse-induced (transient grating, photon echo, coherent anti-Stokes-Raman scattering, four-wave-mixing) optical signals. In the EOM-PMA, the interactions of the system with the relevant laser pulses are incorporated into the system Hamiltonian and the driven system dynamics is simulated numerically exactly. 

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