Rapid-Scan Interferometers

Diffey W M and Beck W F 1997 Rapid-scanning interferometer for ultrafast pump-probe spectroscopy with phase-sensitive detection Rev. Sci. Instrum. 3296-300... 

Rapid scanning interferometers can be used to measure spectra of peaks eluting from a gas chromatograph without prior trapping of the sample (Ref 58)... 

More recently, Weiller (39) has extended this work by performing a detailed rapid-scan FTIR study of M(CO)e (M = Cr or W) in liquid Xe and liquid Kr. A pulsed UV laser source, synchronized to the moving mirror of the FTIR interferometer, was used to photolyze the hexacarbonyls. MCCOsKr was characterized in liquid Kr, Cr(CO)gXe in liquid Xe, and W(CO)sXe in liquid Xe and liquid Kr doped with 5% Xe. M(CO)gKr has... 

Large aperture, high resolution spectrometry can be achieved using interferometers. A scanning system used in conjunction with Fourier transform spectroscopy (see Section 3.4) would facilitate the rapid measurement of complex spectra. As computer facilities are essential, the technique lends itself to automated analysis. 

Another major Hmitation arose from the need to employ a step-scan interferometer. This necessity arose from the relatively slow read-out rates of these first-generation FPAs, which were of the order of only a few hundred Hertz. The read-out rate (or frame rate) of a FPA detector determines the type of interferometer that must be used for FT-IR imaging, as the FPA cannot be triggered (for data transfer) any faster than its maximum read-out (frame rate) speed. As the first-generation FPAs were only capable of frame rates in the hundreds of Hz, and rapid-scanning interferometers required a faster frame rate, the use of step-scan... 

Another example of an fax-infrared Fourier spectrometer is the Bruker IFS 114 (cf. Fig. 50). In contrast to the Poly tec FIR 30, the Coderg FS 4000 and the Beckman FS 720, this spectrometer is a rapid-scan instrument. But the consequences of rapid and slow scanning will be discussed later. Here we shall concentrate on the optical layout. From Figs. 49 and 50, it is evident, that the interferometers are constructed as a modular system and that, by inserting some windows, the compartments of the several modules can be evacuated separately. This is of particular interest for the sample chamber. There, it is an advantage to be able to exchange samples without breaking the vacuum of the whole instrument and to have to reevacuate only the sample chamber. The different modules of the... 

The last quantity to be discussed in this section is maximum path of the movable mirrors. In the slow-scan instruments, usually a lead-screw is employed to drive the mirror with the synchronous motor. And a maximum scan length of the movable mirror of 5—10 cm is achieved without any problems. In the case of rapid-scan instruments however, the customer has to pay for a larger maximum scan length. From a comparison of this quantity for various instruments in Table 3 e.g. No. 4a—d and No. 5a, b) with the prices of the instruments in Table 2, we learn that with increasing prices also the maximum mirror path is increased which determines maximum resolution of the instruments as limited by the mechanics of the interferometer. We recall from our considerations in Sections 2.3, 3.2, 4.6 and 5.1 that, in Fourier spectroscopy, the resolution width is... 

A Michelson interferometer with the facility for step and integrate, and rapid scan operation has been used for Fourier transform PAS. The merits of the two methods were considered. The versatility of this technique for the measurement of the infrared spectra of powdered samples has been demonstrated. Some possible reasons for the distortion of such measurements have been discussed. " FT-PAS has enabled discrimination between K N03 and K NOj and has shown the technique to be suitable for quantitative analysis of solid mixtures. ... 

Hirschmugl CJ (1994) Low frequency adsorbate substrate dynamics for CO/Cu studied with infrared synchrotron radiation. PhD Dissertation, Yale University, New Haven, CT Hirschmugl CJ, Williams GP (1995) Signal-to-noise improvements with a new far-IR rapid-scan Michelson interferometer. Rev Sci Inst 66 1487-1488... 

The main advantage of rapid scanning instruments is the ability to increase the signal-to-noise ratio (SNR) by signal averaging, which leads to an increase of signal-to-noise proportional to the square root of the time. It follows that in a rapid-scan interferometer the SNR is related to the number of scans by the following relationship ... 

Both dispersive monochrometers and Fourier Transform IR (FT-IR) spectrometers can be used in recording SEIRA spectra, but FT-IR spectrometers are more convenient owing to Fellgefs, Jacquino s, and Connees s advantages [128]. The time-resolution of FT-IR spectroscopy is determined by the scan rate of the interferometer. Tens to hundreds of milliseconds time-resolution can easily be achieved by the use of modern rapid-scan FT-IR spectrometers at spectral resolutions of 4 or 8 cm . ... 

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