Instrumentation for Far‐Infrared Spectroscopy

Abstract

The various components of far‐infrared spectrometers are discussed in this article. For measurements above 100 cm −1 , a standard silicon carbide (Globar) source may be used. For longer wavelengths, a high‐pressure mercury lamp is required. When higher radiance is required, synchrotrons emit much higher far‐infrared photon fluxes than either the Globar or the mercury lamp. Pneumatic (Golay) detectors were popular as far‐infrared detectors, as long as the modulation frequency was low. Despite their relatively low sensitivity, pyroelectric bolometers such as the deuterated triglycine sulfate (DTGS) detector are more commonly used because of their better high‐frequency response, which is necessary for Fourier transform infrared (FT‐IR) spectrometry. When very high sensitivity is required, liquid‐helium cooled bolometers are used. Most far‐infrared spectra are measured using an interferometer. In the early days of FT‐IR spectrometry, most interferometers were of the slow continuous‐scan or simple step‐scan variety; lamellar grating interferometers were used for very long‐wavelength measurements. Today, most far‐infrared FT‐IR spectrometers incorporate rapid‐scan interferometers of the same type used for mid‐infrared measurements. A number of special‐purpose instruments are also described, including the Genzel interferometer. All these instruments must be equipped with beamsplitters that are configured for far‐infrared operation. Poly(ethylene terephthalate), also known as Mylar or Melinex, is the most common material used to fabricate far‐infrared beamsplitters but other materials have better efficiency. These include solid silicon or silicon that has been vapor‐deposited onto Mylar.

Noninvasive Electromagnetic Wave Sensing of Glucose

“…Thus, IR spectroscopy has been widely applied in analytical chemistry for characterizing samples in various states such as gases, liquids and solids. Based on different excitation sources, it can be classified into near-infrared (NIR) spectroscopy [ 43 ], mid-infrared (MIR) spectroscopy [ 44 ], and far-infrared (FIR) spectroscopy [ 45 ]. In Section 3.1 , we will discuss NIR and MIR, and separately discuss THz in Section 3.6 , which overlaps with the FIR region.…”

Search prefilters for mid‐infrared absorbance spectra of clear coat automotive paint smears using stacked and linear classifiers

“…The need to carefully and judiciously preprocess the data is necessary for the development of the search prefilters. In this study, spectral line shapes between instruments were matched using convolution and deconvolution functions developed with Nicolet's OMNIC software system. An instrumental line function representative of the two Thermo Nicolet instruments and developed by OMNIC was applied to the Bio‐Rad spectra to ensure that all measurements made by the Bio‐Rad instrument were comparable to spectra collected on the two Thermo Nicolet instruments.…”

Noninvasive Electromagnetic Wave Sensing of Glucose

“…Thus, IR spectroscopy has been widely applied in analytical chemistry for characterizing samples in various states such as gases, liquids and solids. Based on different excitation sources, it can be classified into near infrared (NIR) spectroscopy [41], mid infrared (MIR) spectroscopy [42] and far infrared (FIR) spectroscopy [43]. Herein, we will discuss more on the first two considering the specific application for noninvasive glucose measurement.…”