Time-resolved polarization

Cross A J, Waldeck D H and Fleming G R 1983 Time resolved polarization spectroscopy level kinetics and rotational diffusion J. Chem. Phys. 78 6455-67... 

In principle, pulsed excitation measurements can provide direct observation of time-resolved polarization decays and permit the single-exponential or multiexponential nature of the decay curves to be measured. In practice, however, accurate quantification of a multiexponential curve often requires that the emission decay be measured down to low intensity values, where obtaining a satisfactory signal -to-noise ratio can be a time-consuming process. In addition, the accuracy of rotational rate measurements close to a nanosecond or less are severely limited by tbe pulse width of the flash lamps. As a result, pulsed-excitation polarization measurements are not commonly used for short rotational periods or for careful measurements of rotational anisotropy. 

Buehler, C., Dong, C. Y., So, P. T. C., French, T. and Gratton, E. (2000). Time-resolved polarization imaging by pump-probe (stimulated emission) fluorescence microscopy. Biophys. J. 79, 536-49. 

Bastiaens, P. I. H., van Hoek, A., Benen, J. A., Brochon, J. C. and Visser, A. J. W. G. (1992). Conformational dynamics and intersubunit energy transfer in wild-type and mutant lipoamide dehydrogenase from Azotobacter vinelandii. A multidimensional time-resolved polarized fluorescence study. Biophys. J. 63, 839-53. 

Sakamoto A, Nakamura O, Tasumi M (2008) Picosecond time-resolved polarized infrared spectroscopic study of photoexcited states and their dynamics in oriented poly(p-phenylene-vinylene). J Phys Chem B 112 16437... 

The 3.5- and 8-ntn nanoparticles show well-resolved peaks at 362 and 473 nm, respectively, as well as other features at higher energies. The 4.5-nm particles show a well-resolved peak at 400 nm and a shoulder at 450 nm. It is tempting to assume that in each case, the lowest energy absorption corresponds to the lowest allowed transition (the A exciton) in bulk M0S2. Polarization spectroscopy can be used to determine if this is the case. The lowest allowed transitions in bulk material, the A and B excitons, are polarized perpendicular to the crystallographic c axis. If the lowest allowed transition correlates to the A exciton, then it would be expected to also be a planar (xy polarized) oscillator. However, tire results of polarization studies reveal that the actual situation is more complicated. A combination of time-resolved polarized emission and one-color time-resolved polarized absorption (transient bleach) studies facillitate assignment of the polarizations of the observed nanoparticle transitions. The 3.5-nm particles are emissive and the polarization of the several of the lowest transitions may be determined... 

Doppler-Free Time-Resolved Polarization Spectroscopy of Large Molecules Measurement of Excited State Rotational Constants, J. S. Baskin, P. M. Felker, and A. H. Zewail, J. Chem. Phys. 84, 4708 (1986). 

Solutions were flowed through a suprasil flat cell (0.1 mm thickness) at rates between 0.1 - S.O mL/min in order to minimize any interference from signals produced by secondary photolysis of products. Time-resolved polarization evolution profiles for the formation and relaxation of the polarized radicals were measured at a constant magnetic field and monitored by both a Hitachi 40 MHz digital oscilloscope and a Stanford Research Systems gated integrator/boxcar averager at 5 ns resolution, and both coupled to a 486 PC desk-top microcomputer for analysis. 

Figure 4. a, CIDEP spectrum observed during the photolysis of a flowing GAV solution (flow rate at 5 mlVmin). b, The time-resolved polarization profiles monitored at selected magnetic fields 1, ketyl radicals and 2, phenacyl radicals. 

Lange, W. and Mlynek, J. (1978). Quantum beats in transmission by time-resolved polarization spectroscopy, Phys. Rev. Lett., 40, 1373-1375. 

The pump pulse in time-resolved pump-probe absorption spectroscopy is often linearly polarized, so photoexcitation generally creates an anisotropic distribution of excited molecules. In essence, the polarized light photoselects those molecules whose transition moments are nominally aligned with respect to the pump polarization vector (12,13). If the anisotropy generated by the pump pulse is probed on a time scale that is fast compared to the rotational motion of the probed transition, the measured anisotropy can be used to determine the angle between the pumped and probed transitions. Therefore, time-resolved polarized absorption spectroscopy can be used to acquire information related to molecular structure and structural dynamics. 

Time-resolved polarized IR absorbance spectra of photolyzed MbCO are shown in Fig. 7. The A-state spectra reveal two overlapping features, denoted A and A3 after Ormos et al. (17), with Ai blue-shifted relative to A3. The ratio of the polarized absorbance, AA /AA11, is nearly constant... 

To experimentally probe the CO trajectory after dissociation, ultrafast time-resolved polarized mid-IR spectra of photolyzed h-MbCO in G/W were recorded (34), the results of which are plotted in Fig. 8A. This study was performed in G/W primarily because the flatness of the solvent absorbance spectrum near 2100 cm-1 minimizes temporal distortion of the transmitted femtosecond IR probe pulse, thereby maximizing the effective time resolution of the measurement. Two features are already apparent at 0.2 ps, the earliest time shown, and these features rapidly develop into the docked states denoted Bi and B2. The development of the docked CO spectrum is further quantified by the time dependence of the polarization anisotropy, as defined in Equation (2). The B and B2 polarization anisotropies, plotted in Fig. 8B, evolve exponentially with time constants of 0.20 0.05 ps and 0.52 0.10 ps, respectively, and converge to the same anisotropy of approximately 0.2. According to Fig. 8C, ligand translocation is accompanied by a 1.6 0.3 ps growth of the integrated isotropic B-state absorbance. 

Time-resolved optical experiments rely on a short pulse of polarized light from a laser, synchrotron, or flash lamp to photoselect chromophores which have their transition dipoles oriented in the same direction as the polarization of the exciting light. This non-random orientational distribution of excited state transition dipoles will randomize in time due to motions of the polymer chains to which the chromophores are attached. The precise manner in which the oriented distribution randomizes depends upon the detailed character of the molecular motions taking place and is described by the orientation autocorrelation function. This randomization of the orientational distribution can be observed either through time-resolved polarized fluorescence (as in fluorescence anisotropy decay experiments) or through time-resolved polarized absorption. 

Leenders. R., Van Floek, A., Van lersel. M., Veeger, C. and Visser, A. J. W. G, 1993, Flavin dynamics in oxidized C/ostridium beijerinckii flavodoxin as assessed by time-resolved polarized fluorescence. European Journal of Biochemistry 218, 977-984. Lehrer S.S, 1971, Solute perturbation of protein fluorescence. The quenching of the tryptophyl fluorescence of model compounds and of lysozyme by iodide ion. Biochemistry 10, 3254-3263. 

Bain, A.J. (2002). Time resolved polarized fluorescence studies of ordered molecular systems. In An Introduction to Laser Spectroscopy, Andrews, D.L. and Demidov, A., eds. Chapter 6, pp. 171-210. Kluwer Scientific London. 

Quantum beats can be observed not only in emission but also in the transmitted intensity of a laser beam passing through a coherently prepared absorbing sample. This has first been demonstrated by Lange et al. [872, 873]. The method is based on time-resolved polarization spectroscopy (Sect. 2.4) and uses the pump-and-probe technique discussed in Sect. 6.4. A polarized pump pulse orientates atoms in a cell placed between two crossed polarizers (Fig. 7.12) and generates a coherent superposition of levels involved in the pump transition. This results in an oscillatory time dependence of the transition dipole moment with an oscillation period AF = 1/Av... 

The applied method is an extension of a previously described technique [I] of time-resolved polarization spectroscopy into the femtosecond range. It relies on the creation of a coherent superposition of adjacent states or substates by an optical pulse, which is short compared to the reciprocal of the frequency splitting of the respective states. Such an atomic coherence causes an optical anisotropy in the sample, oscillating exactly with the splitting frequency of the coherently excited states. 

In siammary, the preliminary results presented in this contribution already demonstrate that time resolving polarization spectroscopy offers a number of favourable and new features for direct observation of fast evolving events on a femtosecond time scale and detection of oscillations up to the THz-range. The described technique can be applied to free atoms, liquids and solids to measure coherent transients in groimd and excited states. Since the observed beats result from an atomic interference effect, narrow structures which may be hidden by inhomogeneous broadening mechanisms can still be resolved. 

Fig. 12.1 la,b. Quantum-beat spectroscopy of atomic or molecular ground states measured by time-resolved polarization spectroscopy (a) experimental arrangement and (b) Zee-man quantum beat signal of the Na 3 Si/2 ground state recorded by a transient digitizer with a time resolution of 100 ns. (Single pump pulse, time scale 1 rs/div, magnetic field 1.63 X 10-4 T) [12.40]... 

TIME RESOLVED POLARIZATION STUDIES USING SYNCHROTRON RADIATION... 

These features allow both lifetime and time resolved polarization measurements to be extended into the subnanosecond region and the high repetition frequency greatly facilitates rapid accumulation of data. Time resolved polarization measurements are also made easier by the intrinsic polarization of the light source. 

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