Pump probe signal

Lee S-Y 1995 Wave-packet model of dynamic dispersed and integrated pump-probe signals in femtosecond transition state spectroscopy Femtosecond Chemistry ed J Manz and L Wdste (Heidelberg VCH)... 

Figure C3.5.4. Ensemble-averaged loss of energy from vibrationally excited I2 created by photodissociation and subsequent recombination in solid Kr, from 1811. The inset shows calculated transient absorjDtion (pump-probe) signals for inner turning points at 3.5, 3.4 or 3.3 A.

A final study that must be mentioned is a study by Haitmann et al. [249] on the ultrafast spechoscopy of the Na3p2 cluster. They derived an expression for the calculation of a pump-probe signal using a Wigner-type density mahix approach, which requires a time-dependent ensemble to be calculated after the initial excitation. This ensemble was obtained using fewest switches surface hopping, with trajectories inibally sampled from the thermalized vibronic Wigner function vertically excited onto the upper surface. 

Figure 7.6 (a) Pump-probe signal observed at various probe wavelengths, (b) Close view around... 

We have investigated the vibrational relaxation of Na3F by time-resolved photoionization at the threshold. Among the two isomers of Na3F, we have studied the excited electronic states of the C2v one. The pump-probe signal clearly shows damped oscillations, the period of which is fitted to 390 8 fs, close to twice the previously measured bending mode of Na2F,[l] while the relaxation time is 1275 50 fs. 

Fig. 2. Fit (solid line) of the pump-probe signal (empty circle symbols) using Eqs. (1-3) with a crosscorrelation signal of 180 fs FWHM (dot line).

Fig. 2. Left Pump probe signal of 10 CPT in methanol-water mixtures. The pump was at 390 nm and the probe at 550 nm. Water mole fraction top to bottom 0, 0.18, 0.28, 0.40, 0.48, 0.84.

Figure 1 - Left Raw pump-probe signal for MbCO at 538 nm. Full data scans were recorded for 7 ps here only the first 2 ps are shown since the oscillations have decayed appreciably within this time. The inset shows typical data for cytochrome c (detection wavelength 523 nm) showing no apparent oscillations. Right FFT (dashed) and LPSVD (solid) fits to the MbCO data showing the dominant v7 mode at 667 cm 1.

Fig. 5. Spectrogram of periodically oscillating components of pump-probe signals of polyacetylene probed at 750 nm shown in Fig. 4 and calculated using a Gaussian window function with a HWHM At = 96 fs. S and D denote the stretching modes of single and double bonds respectively. Short-lived satellite-bands (S , S and D , D associated with S and D modes, respectively) indicate the modulation induced by the breather state.

Fig. 1 Polarization dependent pump-probe signals (experiment dotted simulation full). 3. RESULTS AND DISCUSSION...

Therefore the lack of an observable bleach can only be explained by the cancellation of all contributions to the pump-probe signal, which is the case for a perfect harmonic state. It can be shown that the anharmonicity of a vibrational exciton is a direct measure of its degree of delocalization [5]. Thus, we conclude that the free exciton state is almost perfectly delocalized at 90 K. As temperature increases, a bleach signal starts to be observed, pointing to a non-complete cancellation of the different contributions of the total pump-probe signal. Apparently, thermally induced disorder (Anderson localization) starts to localize the free exciton. The anharmonicity of the self-trapped state (1650 cm 1), on the other hand, originates from nonlinear interaction between the amide I mode and the phonon system of the crystal. It... 

Figure 8. Frequency-filtered Na2+ pump-probe signal in comparison to the averaged signal of Fig, 4. The filtered signal measures by how much the Na2+ signal is modulated with the laser frequency. Such modulations occur when there is interference between excitation by the probe pulse and the wavepackets formed by the pump laser pulse. This interference effect causes both the A EJ and the 2 1 Ilg state wavepacket motion to be observable in the signal.

Appendix C Four-Point Correlation Function Expression for Fluorescence Spectra Appendix D Phase-Space Doorway-Window Wavepackets for Fluorescence Appendix E Doorway-Window Phase-Space Wavepackets for Pump-Probe Signals References... 

In this section we apply the same formalism to pump-probe spectroscopy, where one measures the absorption of a probe pulse 2(0 by a molecule excited by a pump pulse E (t). The pump-probe signal can be written as... 

The first term in Eq. (4.3) is reminiscent of Eq. (3.2) for the spontaneous emission spectrum. It represents a doorway wavepacket created by the pump in the excited state, which is then detected by its overlap with a window. The only difference is that the role of the gate in determining the window in SLE is now played by the probe Wigner function W2. In addition, the pump-probe signal contains a second term that does not show up in fluorescence. This term represents a wavepacket created in the ground state (a hole ) that evolves in time as well and is finally determined by a different window Wg [24]. In the snapshot limit, defined in the preceding section, we have... 

The description of pump-probe signals presented in the preceding section can be immediately generalized to heterodyne-detected transient grating spectroscopy as well as to other four-wave mixing techniques. Heterodyne detection involves mixing the scattered field with an additional heterodyne field 4(r). The signal in the ks direction can then be written in terms of the polarization Ts(t) as... 

Here the time ordering of the and 2 fields can be arbitrary we only assume that the field 3 comes after and 2 and does not overlap with them. We can then follow the calculations of pump-probe signals in Appendix E and introduce the joint Wigner distribution for the fields and 2 and for the field 3 and 4 ... 

APPENDIX E DOORWAY-WINDOW PHASE-SPACE WAVEPACKETS FOR PUMP-PROBE SIGNALS... 

We shall calculate here the pump-probe signal (4.1) using the doorway window wavepackets representation. The polarization 3 2(/> to third order in the external field is given in Ref. 17 and is shown to be expressed in terms of the four-point correlation function (2.8) ... 

Figure 1. Pump-probe signal for the A(v = 0) Rydberg level of NO in Ar matrices at 4 K. The plotted signal is the fluorescence in the presence of the pump only minus the fluorescence in the presence of pump and probe pulses, as a function of the time delay between them pump 195 nm, probe 784 nm. The upper curve is the cross-correlation of the pump and probe pulses.

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