Transient holographic grating

The transport coefficients have been measured by the transient holographic grating technique of Thermal Diffusion Forced Rayleigh Scattering (TDFRS) that has already been described in more detail in previous works [85-87] and will only be briefly sketched in the following (Fig. 1). 

Fig. 1 Setup for transient holographic grating measurements. The electro-optic modulators (EOMs) are used for 180°-phase shifts of the holographic grating. The piezo mirror serves for phase matching between the diffracted beam and the coherent reference wave generated by the local oscillator. The setup is a modified version of the one described in [87]...

The transient absorption method utilized in the experiments reported here is the transient holographic grating technique(7,10). In the transient grating experiment, a pair of polarized excitation pulses is used to create the anisotropic distribution of excited state transition dipoles. The motions of the polymer backbone are monitored by a probe pulse which enters the sample at some chosen time interval after the excitation pulses and probes the orientational distribution of the transition dipoles at that time. By changing the time delay between the excitation and probe pulses, the orientation autocorrelation function of a transition dipole rigidly associated with a backbone bond can be determined. In the present context, the major advantage of the transient grating measurement in relation to typical fluorescence measurements is the fast time resolution (- 50 psec in these experiments). In transient absorption techniques the time resolution is limited by laser pulse widths and not by the speed of electronic detectors. Fast time resolution is necessary for the experiments reported here because of the sub-nanosecond time scales for local motions in very flexible polymers such as polyisoprene. 

Waldow, et a/. (12) applied the holographic grating method of Hyde, et a/. (8) to dilute polyisoprenes in good and Theta solvents. Polymer molecular weights were 11, 104, and 302 kDa. Transient relaxations had the same lineshape, represented... 

Fourkas J T and Payer M D 1992 The transient grating a holographic window to dynamic processes Acc. Chem. Res. 25 227-33... 

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