Ac interferogram

Another purpose of the measurement of the pseudosample is that it provides a phase correction needed for Fourier transform of the AC interferogram. The selfcorrection conventionally used in Fourier transformation for one-sign absorption... 

The high-frequency signal, which is caused by the sample s dichroism, is demodulated by the LIA. Nafie [6] called the signal the ac interferogram, Vac(b)-Once the interferograms Vac (8) and Vdc(6) have been transformed to yield the spectra Bac( and Bdc(y), respectively, these spectra are ratioed to give... 

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... 

In summary, the amplitude of the interferogram as observed after detection and amplification is proportional not only to the intensity of the source but also to the beamsplitter efficiency, detector response, and amplifier characteristics. Of these factors, only 7(vo) varies from one measurement to the next for a given system configuration, while all the other factors remain constant. Therefore, Eq. 2.4 may be modified by a single wavenumber-dependent correction factor, 7/(vo), so that the ac signal, 5(8) (in volts), from the amplifier is... 

Figure 7 The Michelson interferometer. The beamsplitter splits light from the broadband source S into two components that travel separate paths to mirrors Ml and M2. The recombined beams incident on the detector D move progressively further and further out of phase as the moving mirror is scanned. The interferogram is a plot of the AC component of the detector signal vs the path difference.

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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