Step-scan Interferometry

E.N. Lewis, RJ. Treado, R.C. Reeder, G.M. Story, A.E. Dowrey, C. Marcott and I.W. Levin, Fourier transform step-scan imaging interferometry high-definition chemical imaging in the infrared spectral region. Anal. Ghent., 67, 3377-3381 (1995). 

Lewis, E.N. Treado, P.J. Reeder, R.C. Story, G.M. Dowrey, A.E. Marcott, C. 8c Levin, I.W., Fourier Transform Step-Scan Imaging Interferometry High-Definition Chemical Imaging in the Infrared Spectral Region Anal. Chem. 1995, 67, 3377-3381. 

Figure 1.3 Modes of the mirror scanning in interferometry (a) continuous-scan mode and (b) step-scan mode.

While an intensity profile at the detector as a function of retardation may be acquired in a step-scan mode, two major drawbacks affect this method of interferogram acquisition. First, the mirror(s) requires stabilization times with mirror inertia and time constants of the control loop determining this parameter in achieving a given optical retardation. Second, additional hardware and control mechanisms need to be incorporated into the spectrometer, thus increasing instrument cost and complexity. In certain cases, however, the utility of a step-scan instrument justifies this additional expense. Historically, the step-scan approach was favored with slow detectors. With the advent of fast detectors and electronics, step-scan interferometry became... 

Experimentation with step-scan interferometry in electrochemistry began in the early 1990s (cf Ref. [23]), and interest has grown steadily ]24, 29-31, 51-54]. Step-scan FTIR spectroscopy provides a means to investigate time- and frequency-dependent processes. Measurements are hmited to reversible systems. However, a great deal of insight can be gained into the molecular transformations that accompany the external perturbation [181-183]. 

The example in Fig. 7.10 demonstrates an application of step-scan interferometry in electrochemistry. Electrode potential modulation was employed, with the... 

In 1991, Osawa and coworkers [101] employed the acronym SEIRAS to describe the Kretschmann coupling ATR technique, and have published a number of papers reporting the exploitation of the phenomenon along with step-scan interferometry (see Sect. 3.5.4.1.4) to study fast surface processes. As with... 

Time-resolved Spectroscopy Finally in this section, the advent of step-scan interferometers has opened up exciting opportunities to study fast, reversible surface processes. Details on step-scan interferometry may be foxmd elsewhere [144] briefly in conventional mode (see in previous text), the mirror moves essentially continuously, with intensity measurements taken at regular intervals (Fig. 12). In step-scan mode, the mirror is paused at each position (retardation), allowing the exploitation of the time-resolved spectroscopy option ofthe spectrometer. Once the mirror has settled at a particular position, a reference point can be taken, after which a reaction can be triggered, that is via a light pulse or potential step, and the intensity measured at regular intervals (Fig. 13). 

A rather new approach to time-resolved spectroscopy that uses modem optoelec-tronic-controlled step-scan methods of Fourier transform interferometry has been suggested [53]. When using step-scan interferometry, the initiation of a reversible event must occur at each mirror position. The time evolution at each mirror position subsequent to initiation is then measured at discrete time intervals. Data processing involves sorting by time in order to produce an interferogram for each sampling time. These interferograms are subsequently Fourier transformed to yield a set of time-resolved spectra. To quote the authors ... 

---