PA-IR spectrograph

The two main differences between a PA-IR spectrograph and a conventional mid-IR dispersive spectrometer are the use of a large planar array detector rather than... 

Figure 13.1 shows the typical layout of a grating-based PA-IR spectrograph. In contrast with the set-up of Heilweil et al. [5], an inexpensive continuous-wave broadband IR source is used, thus decreasing the cost and complexity of the... 

The frame rate of the FPA directly determines the time resolution of a PA-IR spectrograph, while its size can Hmit the achievable bandwidth/resolution and the field of view. Maximum frame rates vary between lOOps and 17 ms per spectrum, depending on FPA type and size. Such time resolutions are similar or significantly better than those possible with continuous-scanning FT-IR spectrometers. It should be pointed out that the Hmiting factor is often not the detection of the IR radiation, but rather the time necessary for the read-out and data transfer. Perfectly optimized electronics could eventually enable a 70 ps time resolution. 

Figu re 13.4 Evolution of the peak-to-peak noise level In 100% noise spectra as a function of acquisition time using an MCT PA-IR spectrograph (with an without pixel binning) and an FT-IR spectrometer. Reproduced with permission from Ref [7]. 

Snively et al. used a PA-IR spectrograph equipped with a 64 x 64 MCT rollingmode FPA to push the time resolution of PA-IR spectroscopy to less than 100 ts per spectrum [27]. The small size and the acquisition mode of this FPA, both contributed to enable such time resolution. First, a smaller FPA allows faster frame rates than a larger one (3.2 ms per image in this specific case), at the expense of bandwidth and/or resolution. Second, the 100% duty cycle of a rolling-mode FPA was put to profit. In a snapshot-mode FPA, all pixels measure the signal intensity simultaneously for -100 ts, but the electronic read-out time can be as... 

Figure 13.9 Comparison of the DIRLD in-phase spectra of isotactic polypropylene recorded in 20s with a PA-IR spectrograph and in 34min using a step-scan FT-IR spectrometer. The FT-IR spectrum has been Inverted for clarity. The dynamic quadrature spectrum and the static PA-IR spectrum of the bulk sample are also shown. Reproduced with permission from Ref [31].

PeUerin et al. assessed the feasibility of IRES measurements with a PA-IR spectrograph equipped with a liquid nitrogen-cooled MCT FPA [37]. They measured the spectrum of different polymer thin films heated to temperatures between 60 and 120 °C. Spectra with a good SNRs were obtained in the fingerprint region for... 

In Figures 13.2b and 13.12a, the spatial resolution along the height of the slit was shown to be on the order of 150 gm per pixel, using a typical PA-IR spectrograph. 

Figure 13.13 Spectral image of a cross-sectioned photographic film recorded using a prism-based PA IR spectrograph coupled to an infrared microscope. Reproduced with permission from Ref [8].

Although still in its early stage of development, PA-IR spectroscopy represents a promising approach to mid-lR spectroscopy. The combination of focal plane array detectors with a spectrograph can ... 

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