Transient grating experimental

The recent advances are bringing about a broadening of the transient grating experimental user community and the range of areas under study, as well as a deepening of the knowledge that can be gained in each area. 

Figure 6. ISRS data from a-perylene crystal at two temperatures, recorded with transient grating experimental arrangement. Oscillations in each sweep due to 80- and 104-cm optic phonons. Data contain sum and difference frequencies that produce beating pattern.

Figure 7. Time-resolved observation of molecular vibrations in CH2Bt2 liquid recorded with a transient grating experimental arrangement using V-polarized pulses. The 5.2-THz oscillations correspond to oscillations of 173-cm bromine bending mode which was excited coherently through ISRS.

Figure 12. ISS data from CSj liquid at 165 K recorded in transient grating experimental configuration with V- and H-polarized excitation pulses. Weakly oscillatory signal indicates that orientational motion is librational in character. Inset fits to data based on models of homogeneous dephasing (broken curve) or inhomogeneous dephased (dashed curve, under data).

Figure 18. The normalized electronic transition frequency correlation function M(t) 1= S(i)] obtained from the experimental three-pulse photon echo peak shifts and transient grating data for IR144 in ethanol (—) total W(t) ( ) ultrafast Gaussian component in M(t) ( ) oscillatory component that arises from intramolecular vibrational motion.

The experimental anisotropy contains information about molecular motion, but is independent of the excited state lifetime. Equation 4 indicates that the orientation autocorrelation function can be obtained directly and unambiguously (within the multiplicative constant r(0)) from the results of a transient grating experiment. 

Photothermal detection has been accomplished in several ways mechanical or electrical thermometer (thermocouple), molecular thermometer, optical interferometry, photoacoustic (PA), thermal lens (TL), or the transient grating (TG) method. Although PA and TL detections are not included in this chapter, some of the experimental results of these methods are referred to in other sections, mostly for comparison purposes with the TG measurement. Characteristic features of these methods are presented in Section 1I.E. 

One of the most important experimental techniques to appear in the last few years has been transient grating spectroscopy and this methodology has numerous important applications. The technique has been used to measure the quantum yield for photodissociation of diphenyl disulfide, and compared to photoacoustic and transient absorption spectoscopic methods. Additional studies have used transient grating spectroscopy to monitor the energetics and dynamics of charge separation of an ion pair into free ions. The approach permits direct measurement of the enthalpy change accompanying formation of the free ions... 

Fig. S. (a) Phase matching in optical wavelength conversion using AT, and K2 to induce the grating and to generate K4 via four-wave mixing process, (b) Experimental setup for infrared-to-visible image conversion using the transient grating induced by infrared (1.06 fim) Nd YAG laser pulses in a dyed nematic liquid crystal film. The reconstructing beam is a CW He-Ne (0.63 / m) laser. The photo insert is a typical observed reconstructed image of the wire mesh object.

In a heterodyne-detected transient-grating (HD-TG) experiment [5,8-11], two infrared laser pulses, typically obtained dividing a single pulsed laser beam, interfere within the sample producing an impulsive spatially periodic variation of the material optical properties. The spatial modulation is characterized by a wave vector which is given by the difference of the two pump wave vectors. The relaxation toward equilibrium of the induced modulation is probed by measuring the Bragg scattered intensity of a second continuous wave laser beam. A sketch of the experimental set-up and details on the laser systems can be found in ref 5 and ref. 10, respectively. 

Taschin, A., Torre, R., Ricci, M., Sampoli, M., Dreyfus,C.,Pick, andR.M. (2001). Translational-rotation coupling in transient grating experiments Theoretical and experimental evidences. EuroPhys. Lett 53 407 13. 

FIGURE 1.13 Experimental results (points) obtained from pump-probe (left) and transient phase grating (right) measurements of MbCO recombination as a function of time, t, following photodissociation. Solid lines were computed from equations (26) and (27), and the best-fit parameter values are listed in Table 1.2. (From Walther, M., Raicu, V., Ogilvie, J. R, Phillips, R., Kluger, R., and Miller, R. J. D. 2005. J. Phys. Chem. B 109 20605-11. With permission.)... 

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