Transient spectral hole burning

The transient spectral hole burning technique has been used to... 

In some kinds of solids, the spectral hole is preserved for time periods longer than the lifetime of any excited state. This phenomenon is called persistent spectral hole burning (PSHB). Otherwise, if the spectral hole can not be preserved for time periods longer than the lifetime of excited state, it is called transient hole (Moemer, 1982). Basic requirements for the PSHB are as follows (Beck, 1998) ... 

If the chromophore has no fluorescence, the FLN method does not work. In this case, we can use the spectral hole burning (HB) method. The HB method has been discussed briefly in Sect. 2.2. Transient holes can be burnt in any impurity... 

Pump-probe absorption experiments on the femtosecond time scale generally fall into two effective types, depending on the duration and spectral width of the pump pulse. If tlie pump spectrum is significantly narrower in width than the electronic absorption line shape, transient hole-burning spectroscopy [101. 102. 103. 104. 105. 106. 107. 108. 109. 110. 111. 112 and 113] can be perfomied. The second type of experiment, dynamic absorption spectroscopy [57, 114. 115. 116. 117. 118. 119. 120. 121 and 122], can be perfomied if the pump and probe pulses are short compared to tlie period of the vibrational modes that are coupled to the electronic transition. 

As evidenced from the above discussion, vibrational line shapes provide information mostly about intermolecular structure. Transient hole burning and more recently echo experiments, on the other hand, can provide information about the dynamics of spectral diffusion. The first echo experiments on the HOD/ D2O system involved two excitation pulses, and the signal was detected either by integrating the intensity [20] or by heterodyning [22]. The experiments were analyzed with the standard model assuming Gaussian frequency fluctuations. The data were consistent with a spectral diffusion TCF that was bi-exponential, involving fast and slow times of about 100 fs and 1 ps, respectively. 

During the last decade, picosecond transient and permanent hole burning spectroscopy have been used to study the interaction between organic glasses or polymers and the electronic state of the nonpolar solute 3,6-dimethyl-l,2,4,5-tetrazine, the spin-conversion relation of the methyl groups, the structural relaxation and the behavior of spectral holes.378-395,445,446... 

Pump-probe absorption experiments on the femtosecond time scale generally fall into two effective types, depending on the duration and spectral width of the pump pulse. If the pump spectrum is significantly narrower in width than the electronic absorption line shape, transient hole-burning spectroscopy [101. 102. 

The observed transient absorption data alone are not able to eliminate Model B2. Additional information comes from hole-burning experiments (Johnson et al., [22]). In these experiments performed at very low temperatures narrow zero phonon holes were observed with a spectral width corresponding to a time constant of approximately 1 ps. From these data one can deduce that the first reaction process starting from the lowest vibrational level of P is the slower, the 1.4 ps process. The faster 0.3 ps component must be (as it is not related with vibrational relaxation, see above) the second process in the reaction scheme. Since the important features of the reaction processes do not change strongly with temperature one may discard Model B2 at room temperature as well. 

The HB effects in A showed transient character (THB). Very broad transient holes ( -145 cm-1) were observed in the low temperature A spectra depending on chopper frequency and burning laser intensity. These results are in agreement with the data presented in l9, 23 on PS II. No sharp hole superimposed on the broad hole was observed due to rather low spectral resolution of our A set up. 

---