Dc interferogram

The procedure used to acquire the data was as follows. First a dc interferogram is measured with the 200-MHz transient recorder in the step-scan mode without sample excitation. The measured interferogram is used to calculate the phase spectrum, 0v, and the single-beam background spectrum, Sr v). The time-resolved measurement at a given OPD is then started by a laser flash at each step. The 200-MHz transient recorder measures the time-domain signal from 100 ns to 20 ps and the 200-kHz recorder monitors from 5 ps until the end of the reaction. At every step, several photocycles are accumulated to improve the SNR. Because of the fact that... 

Figure 2. Signal at the detector from a monochromatic source. This interferogram shows the sinusoidal variation of the signal about a DC offset as a function of the retardation. 

Thus the interferogram of a monochromatic source has the form depicted in Fig. 2a. The signal goes through the constant-dc value (0.5 7 (v)) at all points where <5 = n A (where n is an integer). 

Figure 7.45. Potential-difference unpolarized ATR-SEIRA spectra of 4-mercaptopyridine (PySH) SAM on 20-nm-thick (80-nm-size particles) Au evaporated electrode in 0.1 M HCIO4. Reference potential was -0.1 V (SCE). Arrows show changes of peaks for positive shift of electrode potential from -0.3 to -1-0.4 V. Spectra were recorded using Bio-Rad FTS 60A/896 FTIR spectrometer equipped with dc-coupled MCTdetector and bandpass optical filter transmitting between 4000 and 1000 cm". Spectrometer was operated in rapid-scanning mode and spectra were collected sequentially during potential sweep at 5 mV s". Sixty-four interferograms were coadded to record each spectrum, which required about 10 s. Reprinted, by permission, from K. Ataka, Y. Hara, and M. Osawa, J. Electroanal. Cham. 473, 34 (1999), p. 37, Fig. 3. Copyright 1999 Elsevier Science S.A.

It can be seen that / (5) is composed of a constant (dc) component equal to 0.5/(vo) and a modulated (ac) component equal to 0.5/(vq) cos 2tivo5. Only the ac component is important in spectrometric measurements, and it is this modulated component that is generally referred to as the interferogram, /(8). The interfero-gram from a monochromatic source measured with an ideal interferometer is given by the equation... 

For a monochromatic source of frequency, v, the interferogram is a cosine function of the frequency and x and the path difference. By extension, the interferogram of a polychromatic source appears as the cumulative sum of many individual cosine interference patterns. The interferogram consists of two parts a constant (DC) component and a modulated (AC) component. The I (x) or AC component is called the interferogram and is given by... 

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