## 5 Applications of Mid-IR Supercontinuum Generation  
Thanks to a broad Mid-IR range coverage, high coherence, and good beam quality, Mid-IR supercontinuum sources are potential candidates for a variety of applications in domains such as spectroscopy, sensing, biology, metrology, and spectral imaging [43, 47]. As an example of this, the IR signature of propanol and acetone has been detected by fibers evanescent wave spectroscopy (FEWS) using a chalcogenide MOF [47]. In this experiment, it was demonstrated that an exposed-core chalcogenide MOF, as shown in Figure 7, can be more sensitive to the environment than classical single-index fibers, such as those used in ref. [23]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Fiber Composition** & **Spectral Coverage** & **Pump Wavelength (Pulse Duration)** & **Output Average Power** & **References** \\ \hline As\({}_{2}\)S\({}_{3}\) & 2.1–32 \(\upmu\)m & 2.5 \(\upmu\)m (100 fs) & - & [36] \\ As\({}_{2}\)S\({}_{3}\) & 1–26 \(\upmu\)m & 1.55 \(\upmu\)m (400 fs) & - & [38] \\ AsSe\({}_{2}\)-As\({}_{2}\)S\({}_{5}\) & 1.2–5.37 \(\upmu\)m & 3.3 \(\upmu\)m (200 fs) & 214 mW (input) & [46] \\ As\({}_{38}\)Se\({}_{2}\) & 1.9–7.1 \(\upmu\)m & Cascading from 1.55 to 4.5 \(\upmu\)m (3 ns) & 6.5 mW & [45] \\ Ge\({}_{10}\)As\({}_{22}\)Se\({}_{68}\) & 1–11.5 \(\upmu\)m & 4 \(\upmu\)m (252 fs) & 35.4 mW & [22] \\ Ge\({}_{10}\)As\({}_{22}\)Se\({}_{68}\) & 1–8 \(\upmu\)m & 4 \(\upmu\)m (252 fs) & 57.3 mW & [22] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Mid-IR supercontinuum generation obtained in chalcogenide MOFs. Figure 6: (a) Cross section of the AsSe\({}_{2}\)–As\({}_{2}\)S\({}_{5}\) hybrid MOF. (b) Output spectrum of the mid-infrared ( Mid-IR) supercontinuum obtained by pumping at 3389 nm. Adapted with permission from ref [46], copyright The Optical Society, 2014. Mid-IR spectral imaging, combined with data mining algorithms, has been utilized as an aid for diagnosing some types of cancers [48; 49; 50; 51]. The acquisition speed and penetration depth of traditional Mid-IR spectral imaging is subject to low brightness and lack of flexibility for the delivery and detection of light [52]. Therefore, intense laser sources with high signal-to-noise ratios become an ideal choice for rapid acquisition through the Mid-IR range. Quantum cascade lasers (QCL) were once used in Mid-IR spectral imaging systems to reduce the acquisition time, but the limited frequency coverage of QCLs cannot satisfy the diagnostic requirements and maintain, at the same time, the simplicity of the system at a reasonable cost. Thus, supercontinuum sources were selected for broadband Mid-IR spectral imaging. For example, ZBLAN-fluoride-fiber-based supercontinuum sources, with a 2-4.5 um spectral range, were selected to be integrated into Mid-IR spectral imaging systems demonstrated in the past few years [53; 54; 55]. In 2012, [PERSON] et al. presented, for the first time, a high-resolution contact-free infrared microscope. By using a 1900-nm fiber laser to pump 10 m of ZBLAN fiber, the generated supercontinuum spanned from 1.4 to 4.0 um. The system was tested by a mixture of oil and water and resolutions of 35 um and 25 um for the water absorption image and oil absorption image were obtained, respectively, as shown in Figure 8[53]. In 2017, [PERSON] et al. reported a mid-infrared spectral imaging system for the rapid assessment of cells for cytological diagnosis, consisting of a ZBLAN-fiber-based supercontinuum source, a fast acousto-optic tunable filter (AOTF), and a high-resolution thermal camera. The AOTF enables the system to record a 100-wavelengths image cube and 300 k pixels in 2 s, so that it can be used to test the cells of a living person. By comparison, the system proved to have a higher spectral resolution than a Fourier transform infrared (FTIR) system. Restricted by the filter inside the thermal camera and the range of the supercontinuum source, collection of samples of colon cells could be imaged, nevertheless, in the 2.87-3.7 um spectral range [54].