Photon echo optical free induction decay

As the spacing ofthe real part ofthe eigenvalues Ej—Ef) is uncorrelated, one expects severe destructive interference effects for p(t), when more than a single ME is driven by the field. Thus, coherent optical effects such as photon echoes or free induction decay experiments can be conducted only under special excitation conditions as follows ... 

The important point to note here is that the photon echo does not suffer from the triplet state bottleneck in the same sense as hole-burning or optical free induction decay. It is only the repetition rate in the photon-echo experiment that is limited by the triplet state decay rate. Morsink et al. showed that at low temperature ( 2 K) the photon-echo hfetime of dilute PTC-A,4 and PTC-d,4 in p-terphenyl crystals is identical to the fluorescence lifetime. This implies that at this temperature pure dephasing processes are absent. The homogeneous linewidths are therefore 5.9 MHz (PTC-rf,4) and... 

Dephasing can be studied either in the time domain (photon echo PE [171,172], optical free induction decay (OFID) [173, 174] or in the frequency domain (hole burning) [175-177]. With these techniques, the homogeneous broadening can be circumvented and the pure homogeneous width can be measured. 

In case the effective laser linewidth is less than the hyperfine splitting(s) excitation will prepare a two-level system. The effect of spin-flips on the coherence in this system will then manifest itself as a 7 ,-type process. No beats are expected in the decay of the optical free induction. With broadband excitation that spans some of the hyperfine splittings spin-flips will be monitored as 7 2-type processes and quantum beats are expected in the photon-echo intensity vs probe delay. Burland et al. also demonstrated the feasibility of optical nutation in this system from which in principle, as from the OFID, the transition dipole could be calculated. 

In the case of coherent laser light, the pulses are characterized by well-defined phase relationships and slowly varying amplitudes (Haken, 1970). Such quasi-classical light pulses have spectral and temporal distributions that are also strictly related by a Fourier transformation, and are hence usually refered to as Fourier-transform-limited. They are required in the typical experiments of coherent optical spectroscopy, such as optical nutation, free induction decay, or photon echoes (Brewer, 1977). Here, the theoretical treatments generally adopt a semiclassical procedure, using a density matrix or Bloch formalism to describe the molecular system subject to a pulsed or continuous classical optical field, which generates a macroscopic sample polarization. In principle, a fully quantal description is possible if one represents the state of the field by the coherent or quasi-classical state vectors (Glauber, 1965 Freed and Villaeys, 1978). For our purpose, however. 

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