Lock-pulse selective spectroscopy

Fig. 9.1.4 [Rom2] Pulse and gradient scheme for lock-pulse selective spectroscopy. The slice selection is based on selective spin locking.

St -> Sn Spectra.—A description has been given of a method for recording ultrafast absorption spectra using a passively mode-locked ruby laser with a ruby amplifier, a pulsed flashlamp probe source, and streak-camera detection for ps time resolution. Results for the dye 3,3 -diethylthiatricarbocyanine in methanol were reported.2870 These results can be compared with those obtained by an alternative method 29711 which permits nm spectral resolution and ps time resolution over the entire visible region, and which was first used on the Sx -> Sn absorption of 3,3 -diethyloxadicarbocyanine iodide, and which has recently been used to record the Si - Sn absorption spectra of bis-(4-dimethylaminodithio-benzil) nickel(n), and of SnIV, Pd11, and Cu" porphyrins.298 The use of time-resolved Si - Sn, Ti - Tn absorption and emission spectroscopy to assist in the selection of laser dyes has been illustrated with respect to anthracene and its derivatives.299 Si - Sn Spectra of coronene, 1 2-benzanthracene, l 12-benz-perylene, 1,2,3,4-dibenzanthracene, and benzo[6]chrysene in poly(methyl methacrylate) and toluene have been reported, the method of detection being modulation spectrophotometry, for which it is claimed that species of lifetime down to... 

The high time resolution that is achievable with pulsed or mode-locked lasers (Chap. 11) opens the possibility for studying the dynamics of collision processes and relaxation phenomena. The interesting questions of how and how fast the excitation energy that is selectively pumped into a polyatomic molecule by absorption of laser photons, is redistributed among the various degrees of freedom by intermolecular or intramolecular energy transfer can be addressed by femtosecond laser spectroscopy. 

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