## 3 IR Synchrotron Radiation Sources and FTIR Spectroscopy Techniques  
The first X-ray experiments with synchrotron radiation were performed in the 1960s, while the first developments of the synchrotron radiation in the IR region were obtained in the 1970s, and the first facility for the use of infrared synchrotron radiation (IR-SR) was established at Daresbury at the beginning of the 1980s [2]. Later, many other beamlines dedicated to infrared SR were established, and SR-\(\upmu\)FTIR applications nowadays span from solid-state physics, gas-phase studies, surface science, earth and planetary science, archaeology to life sciences, biomedicine, biophysics, nano spectroscopy, and imaging [5,6]. Bending magnets are generally adopted for developing an IR-SR source that exploits the emission from the dipole magnets that curve the electron beam into a closed trajectory. Since SR in the infrared wavelength range is characterized by a large size and intrinsic divergence of the beam, it is necessary to use suitably sized optics for transferring and focusing the infrared beam from the large exit port of the storage ring to the entrance of the associated spectrometer. The first optical component of an infrared beamline is a flat mirror that is adopted for deviating the emitted photon out of the bending magnet region to another flat or focusing mirror. The first mirror is named the extraction mirror, which constitutes a very important element of the beamline. Particular care is required for its positioning and shaping. In Reference [6], details on the optical setups used for infrared beam propagation control are reported. The principal advantage in using an IR-SR for spectroscopy is related to its very high brilliance. This physical parameter is defined as the number of photons per unit of time(s) per 0.1% of bandwidth and the results of at least two orders of magnitude greater than a thermal source. In Figure 3, the comparison between the calculated IR-SR brilliance of a 3 GeV SR source and a Globar thermal source is reported. The high brilliance is extremely useful for obtaining high-quality spectra from heterogeneous and complex samples. In addition, IR-SR is strongly polarized, pulsed, and characterized by a broadband emission. It is important to note that some laser sources have similar characteristics as far as concerns brightness, but the IR-SR source is the only one with a broadband emission covering the entire infrared wavelength range (from far-IR (i.e., 250-300 \(\upmu\)m) to near-IR (i.e., 0.7-1 \(\upmu\)m)) [28]. As said before, FTIR experiments require the use of a spectrometer system. Commercial Fourier transform infrared microspectrometers can be used with IR-SR sources, and the operation modalities are the same as for thermal sources. Array detectors, known as focal plane arrays (FPAs), are generally used, since they offer the advantage of reducing the acquisition time [29]. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Peak (cm\({}^{-1}\))** & \multicolumn{4}{c}{**Assignment**} \\ \cline{2-4}  & **DNA/RNA** & **Protein** & **Lipid** & **Carbohydrate** \\ \hline
1291 & & Amide III (–N–H \(\delta\), C–N \(\upnu\)) & \\ \hline
1227 & PO\({}_{2}\)\({}^{-}\) as. \(\upnu\) & C–O–P \(\upnu\) & \\ \hline
1207 & C–H ring \(\delta\) & & \\ \hline
1171 & Sugar-phosphate & & \\  & backbone vbr. & & \\ \hline
1166 & & CO–O–C s. as. \(\upnu\) & \\ \hline
1143 & Ribose C–O \(\upnu\) & & \\ \hline
1124 & C–O \(\upnu\) & & \\ \hline
1100 & P–O–C s. \(\upnu\) & & \\ \hline
1086 & PO\({}_{2}\)\({}^{-}\) s. \(\upnu\) & C–O–P \(\upnu\) & \\ \hline
1058 & C–O \(\upnu\) & & \\ \hline
965 & PO\({}_{4}\)\({}^{-}\) s. \(\upnu\) & C–O \(\upnu\), C–C \(\upnu\) (a. a.) & \\ \hline \hline \end{tabular}
\end{table}