Optical pumping transient signals

When the pump-probe delay is varied slowly and continuously (i.e., both parameters are varied simultaneously), the high-frequency oscillations due to the optical phase of the wavepacket can be resolved in the transient signal, as shown by Blanchet et al. [27], who monitored the wavepacket motion and... 

The lifetimes of the sublevels of the excited triplet state of the Rh-trisdiimine complexes have been determined using the microwave recovery and adiabatic rapid passage techniques mentioned in Sect. 4.2. At (pumped) liquid helium temperatures it turned out that the triplet state sublevels have distinct lifetimes. As an example, we show in Fig. 8 the optically detected adiabatic transient signal as monitored for the zero-field D -1 resonance, at 2320 MHz, of the photo-excited [Rh(bpy)3] (0104)3 single crystal, at 1.4 K. The microwave frequency scan was at a rate of 2 x 10 Hz/s. Similar transients were obtained by rapid scans through the zero-field microwave transitions for the other compounds of the [Rh(phen)u(bpy)3 n] (0104)3 series. The transients fitted a biexponential function of the form... 

The derivation of equation (17.21) for the width of the magnetic resonance signals observed in an optical pumping experiment is now quite straight-forward. A study of the time-dependent solutions of equation (17.55) (Problems 17.9 and 17.10) leads to equations which we have discussed earlier in connection with the measurement of the longitudinal and transverse relaxation times in transient experiments. ... 

Fig. 7.2 Two-beam experimental setup for femtosecond transient absorption studies using a white light continuum. A commercially available CPA 2101 laser system delivers the pulses. Ultrashort tunable visible pulses are obtained by the NOPA optical parametric converter. A chopper wheel is used to cut every second pump pulse in order to compare the signal with and without the pump. The white light continuum is generated by a sapphire disc. The time delay between the pump and probe pulses is adjusted by the optical delay rail...

The transient absorption (double-resonance) technique allows us to extend this study to excited vibrational levels of nonradiant states and especially of the ground electronic state. The s> level of the lower electronic state (e.g., of the So state) involving v" quanta of an optically active mode o>" is populated by the pumping pulse. Its population is monitored by the delayed probe pulse inducing a transition S> -> 0 > to the vibrationless level of the higher (Sj) state followed by the Si Sq fluorescence. The frequency of the probe pulse (equal to cu = cuoo v /o)") is too low for excitation of molecules from the vibrationless level 0>. On the other hand, the /> 0 > transitions are forbidden. The redistribution rate may thus be deduced from the dependence of the fluorescence signal on the delay between the pump and probe pulses (Maier et ai, 1977). 

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