Light pulse information

Information-bearing light pulses travel through the glass of fiberoptic cables, a revolution in longdistance communication. 

More direct information on the energetics of the photopolymerization process is afforded by DSC measurement with UV-initiation of the reaction. Under single pulse excitation the integral heat evolved per light pulse is a measure for the product nAH and from the ratio of the signal amplitudes at t = 0 and t -+ co, respectively,... 

Addressing molecular switches remains a problem as well. The use of diffraction-limited focused light pulses provides a useful start, but subdiffraction optical techniques need to be improved and implemented to transfer information into and out of these molecular arrays. At present near-field optical techniques are relatively slow, so that although they provide better spatial resolution, the speed of information access is somewhat limited. 

The plane-polarized light pulses characteristic of mode-locked lasers also provide an ideal excitation source for time-dependent fluorescence depolarization studies although conventional excitation sources can be used. If the rotational relaxation time of the excited molecule is comparable to its fluorescence decay time, then the vertical (I ) and horizontal (Ix) components of the fluorescence decay observed through suitable polarizers following excitation by polarized li t pulses, may be analysed to provide information concerning the size and motion of die molecule and Sect. 5. However, if only the true fluorescence decay characteristics are of interest it is necessary to compensate for these emission anisotropy effects Perhaps the simplest technique is to analyse only that component of fluorescence emitted at 54.7° to the direction of pdarization of the excitation source, the so-called magic-angle ... 

These methods have been applied to studying various natural light-induced biomolecular processes such as photosynthesis and vision. With modem pulsed-laser techniques one can use light pulses as short as a few femtoseconds, or less, and this gives information about the very earliest stages of important photochemical reactions. 

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