Transient grating decay

Figure 2. Transient grating decays for 9,lO-bis(methylene)-anthracene labeled polyisoprene in dilute hexane solution. Tg and Tx are the diffraction efficiencies of the grating for the probe beam polarized parallel and perpendicular to the excitation beams (see Equations 1 and 2). The two curves are initially different because the excitation beams create an anisotropic orientational distribution of excited state transition dipoles. As backbone motions occur, the transition dipoles randomize and the two curves coalesce. Both curves eventually decay due to the excited state lifetime. The structure of the anthracene-labeled polyisoprene is also displayed, with the position of the transition dipole Indicated by a double arrow. (Reproduced from Ref. 7. Copyright 1986 American Chemical Society.)...

Figure 7.16 Transient grating decay signals recorded (lighter curves) for excitation into the pure electronic origin at = 2 K, A =...

Figure 7.17 Transient grating decay signals (A = 20pm) recorded for excitation into the pure electronic originof04 force =2.1 x 10" mol/mol and varioustemperatures (a) 36 l< (b)24K (c) 10 K and (d) 2K.

Figure 7.20 Same as Figure 7.19a but for a stronger interaction between resonantly coupled pentacene guests. The values of M,1 =5.7 x 10 cm and 1 +i = 1-86 x 10 s have been chosen to obtain the best fit to the transient grating decay curve (d) in Figure 7.16. 

Picosecond-resolved thermochemical information can be extracted from the evolution of a transient grating produced by the crossing of two laser pulses and interrogated with a third short pulse of light. Several groups have applied this method to thermodynamic questions about the decay of excited states and the evolution of excited states into reactive intermediates. 

Figure 19. Comparison of calculated and measured signals using the M(t) shown in Fig. 18. (a) Three-pulse echo peak shift, (b) transient grating, and (c) transient absorption. A pulse duration of 16 fs (20 fs for transient grating) and a detuning of 230 cm-1 are used in the calculated signals. The peak near T = 0 in the transient grating and transient absorption signals, usually referted to as the coherent artifact, arises from the ultrafast decay (sum of intramolecular vibrational contribution and -100 fs ultrafast solvation dynamics) in M(t).

Homoedelle BJ, Edington MD, Diffey WM, Beck WF. Stimulated photon echo and transient grating studies of protein-matrix solvation dynamics and interexciton radiationless decay in a-phycocyanin and allphycocyanin. J Phys Chem 1998 102 3044-3052. 

The vibronic spectra of Do — Di — D2 electronic states recoded by da Silva Filho et al. [45] revealed resolved vibrational structures of the Do and D2 electronic states and a broad and structureless band for the Di state. A slow ( 3-20 ps) and fast k, 200 fs) relaxation components are estimated for the Dq D2 transition in a (femto)picosecond transient grating spectroscopy measurements [16]. The fast component is attributed to the Do D2 transition and a nonradiative relaxation time of 212 fs is also estimated from the cavity ringdown (CRD) spectroscopy data [42]. Electronic structure results of Hall et al. [107] suggest that the nonradiative Do D2 relaxation occurs via two consecutive sloped type CIs [66,108]. We developed a global model PESs for the Do — Di— D2 electronic states and devised a vibronic coupling model to study the nuclear dynamics underlying the complex vibronic spectrum and ultrafast excited state decay of N +[20]. 

FlG. 14.1. The decay rate of the transient grating signal versus 92 (9 is the angle between the pump pulses) for anthracene crystals at 10 and 20 K (23). The magnitude of the slope is proportional to the diffusion constant of the excitations in the crystal. With increasing temperature, the diffusion constant decreases. The average diffusion constant obtained from these data is about 10 times larger than the value expected for incoherent exciton motion (25). 

Fig. 14.1 The decay rate of the transient grating signal versus 92 422...

Figure 15 shows examples of decays of transient grating signal (the intensity of the diffraction pattern) observed for an n-Ti02 (100) electrode by excitation at 360 nm and probing at 670 nm [33]. The decays are related with the rate of electron-hole recombination near the n-Ti02 surface. 

Fig. 3. (a) The temporal dependence of the dillraclion of a CW He-Ne laser from a transient grating induced by two nano.second Nd YAG second harmonic laser pulses in a nematic film (PCB 40 m thick io-meotropically aligned) (after [17]). Time scale is 20 ns/div. Similar ultrasonic wave generation was also observed in a smectic liquid crystal film 117bj. (b) The dynamics of the thermal grating formation and decay in a nematic film as monitored by a CW He-Ne probe laser diffraction. The grating wave vector K - K2 is perpendicular to the director axis, (c) Same as in (b), but for K K2 along the director axis. 

In 1971, Eichler, et al of the I. Physikalisches Institut der Technischen Universitat Berlin, reported the first detection of a transient grating. They used a ruby laser to produce a thermal refractive index grating in dye-containing methanol. In 1972, they reported additional measurements, including the time decay of the grating due to thermal diffusion, on a time scale of 1 ms. 

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