The progress in development of a dual-comb spectrometer for detection of traces of explosives at stand-off distances is reported. The spectral range of the spectrometer was extended to 1205-1305 cm-1, the stand-off distance was shortened to 0.5 m to access more potential use-cases, and the speckle contrast was decreased to 0.3%. Tests of the dual-comb spectrometer on RDX and PETN deposited on glass surfaces with a surface concentration of ~10 g/cm2 deposited using a sieving method will be presented and compared with the measurements carried out using a laboratory grade FTIR instrument.
A straightforward multi-scale infrared (IR) spectroscopic characterization of anisotropic polymer nanofibers for material research and biomedical applications is presented. Polarization dependent IR spectroscopies with spatial resolutions from a few mm down to a few 10 nm (by atomic force microscopy-based infrared spectroscopy, AFM-IR) and time resolutions from the min to µs range (by infrared dual-comb polarimetry, IR-DCP) are used. Compared to AFM-IR, which measures the absorption via the photothermal expansion, and IR ellipsometry, which measures amplitudes of sand p-polarized radiation and their phase differences, IR-DCP measures separately s-and p-polarized amplitudes and phases
A proof-of-concept of a scanning stand-off dual-comb spectrometer for explosives detection and identification at 3 m distance is demonstrated. Detection of two types of explosives: RDX and PETN on various surfaces was carried out in reflection-absorption and backscattering modes. A scanning area of 18 cm X 18 cm (400 pixels) was covered in ~2.5 sec. Identification method was based on Pearson’s correlation coefficients between the recorded reflection-absorption (backscatter reflection) spectra and transmission (reflection) FTIR of substances, with baseline subtraction using the asymmetric least square smoothing algorithm. Detection limits of the laboratory system of < 2 ug/cm2 were achieved.
In this paper, we present a thorough comparison of mid-infrared techniques, focusing on the two dominant solutions: QCL and FTIRs. Consequently, we will cover the technical challenges the DCS technique has to overcome to be superior to the FTIR technique. Pushing the DCS technique, we manage to get µs time resolution for up to 131 ms acquisition time as well as < 1 ms time-resolution for reactions which take > 10s. Furthermore, we have improved the spectral coverage of QCL DCS covering more than 100 cm-1 . Overall, the combination of high-speed, spectral bandwidth and high-brightness of this highly coherent source puts DCS at an advantage compared to FTIRs for a plethora of applications, such as liquid analysis (e.g. protein analysis, dioxin measurement, stopped flow), fiber applications and high-resolution spectroscopy. As such, we will give a comprehensive review of applications which are targeted today using QCL DCS. This covers bio-, environmental/gas, combustion as well as water analysis.
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