Time-domain spectroscopy data processing

Prior to Fourier transformation the time domain data may be modified by multiplication by a function q(t), a process commonly called digital filtering. By suitable choice of q(t), digital filtering may be used in NMR spectroscopy to enhance sensitivity, to improve spectral resolution, or to avoid truncation effects. Conceptually, there is very little difference between filtering of ID and 2D NMR spectra, so the treatment here may later be extended readily to the two-dimensional case. 

All these studies with femtosecond pulses on the primary photochemical processes of rhodopsin were done by means of transient absorption (pump probe) spectroscopy [10]. However, absorption spectroscopy may not be the best way to probe the excited-state dynamics of rhodopsin, because other spectral features, such as ground-state depletion and product absorption, are possibly superimposed on the excited-state spectral features (absorption and stimulated emission) in the obtained data. Each spectral feature may even vary in the femtosecond time domain, which provides further difficulty in analyzing the data. In contrast, fluorescence spectroscopy focuses only on the excited-state processes, so that the excited-state dynamics can be observed more directly. 

Other processing techniques for analysis of F.t.-i.r. data have been developed in order to obtain the maximum of information from the spectra. The advances made in time-resolved techniques, which sample only a portion of the interferogram, permit obtaining of spectra in the microsecond domain this will lead to additional applications of F.t.-i.r. spectroscopy such as the study of dynamic and kinetic processes. 

---