Chirped interferogram

Figure 3.11. (a) Chirped interferogram (b) phase-corrected spectrum of the source calculated from this interferogram (c) almost completely unchirped interferogram reconstructed from this spectrum. (Reproduced from [7], by permission of the Society for Applied Spectroscopy copyright 1974.)... 

Fig. 42. Interferogram I s) obtained with and without chirping and corresponding spectrum 1(0) with two bands centered at vi and va. In the case of chirping, the intensity of the grand maximum of the interferogram is shifted away from s = 0 to different path differences si = [n(vi) — l]i and S2 = [n v2) — l]

To calibrate the dispersion of the interferometer and the spacing of frequencies on the linear array, a nonresonant sample (sapphire) was used. It was found that the OPA signal and the anti-Stokes are almost transform limited and nearly identical, and the interferometer had negligible dispersion. Therefore, only the angular dispersion of the wavelengths on the array needed to be characterized. To calibrate the chirp introduced by the 85 cm BK7 bar, the interferogram was sampled from a sample of acetone. Acetone has a narrowly... 

In this case there is no point at which all the wavelengths are exactly in phase and the interferogram is said to be chirped. For most interferograms, the amount of chirping is small, but in a few unusual cases, 0 can vary rapidly (see Section 3.2). Figure 2.12 shows an interferogram that exhibits a small amount of chirping. 

Figure 2.12. Typical interferogram of a blackbody-type source in the region of the centerburst measured by a rapid-scanning interferometer. The slight asymmetry indicates a very small amount of chirping.

The ideal material for a beamsplitter would have a refractive index greater than 5. For example, if n = 5.0 and 0 = 45°, Rp = 0.56 and Rg = 0.32, so that = 0.98 and V[p = 0.87. Even if materials could be found with such high refractive indices could be found, their refractive index would have to be constant across the entire spectral range if all wavelengths are to be in phase at the same point. (The effect of dispersion on the interferogram has been called chirping see Section 2.5.)... 

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