Infrared spectroscopy is an ideal tool for characterizing textiles for identification or classification purposes. In this application note, we showcase how the ARCoptix FTIR can be used for such purpose both in the near‑infrared (NIR) and mid-infrared (MIR) without using contact sampling methods, typically ATR. The results presented here are mostly qualitative and intend to display the features observable with our instruments without further analysis, as this would fall out of the scope of this document.
Experimental setup - NIR setup
- ARCLIGHT-NIR: NIR light source with QTH bulb
- FTNIR-L1-025-2TE: FTIR spectrometer with 2TEC 0.9-2.5µm InGaAs detector
- FIB-NIR-600-100: Low-OH multimode silica fiber with a 600µm core diameter
- OEM-PART-LFC-CAF2: SMA fiber coupler with CaF2 lens
- PART-DRS-NIR: Diffuse reflectance standard for NIR
NIR setup (reference measurement) using the ARCLIGHT-NIR and an optical fiber collimator for free-space acquisition
- FTMIR-CMP-120-4TE: FTIR spectrometer with 4TEC 2-12µm detector,common-path output
- OEM-PART-DRP: Parabolic reflector for diffuse reflectance measurement
- PART-DRS-MIR: Diffuse reflectance standard for MIR
MIR Textile characterization using a common path configuration
Experimental results
The experimental parameters in both setup were identical in order to have a fair comparison between these two methods. The instrument resolution was set to 4cm-1, with Norton-Beer weak apodization function. The baseline was acquired with 64 averages, which corresponds to ~12s of acquisition time. The white reference for the NIR is made of Teflon, while the MIR reflectance standard is made of gold. The sample spectra are then measured using 32 averages, ~6s per scan.
Three different samples were measured:
- Pure cotton
- Purely synthetical fiber
- Mixed fabric with 55% of cotton and 45% of polyester.
Absorbance measured using the NIR setup (top) and MIR setup (bottom)
Experimental results
Both sets of traces indicate good quality measurements, with distinguishable features in both spectral range. In this experiment, the data between 833cm-1 and 1000cm-1 (MIR setup) was discarded as the signal-to-noise ratio was insufficient in that range. This is mostly due to the spectral balance of the emitter used (SiC globar burning at ~1550K), which outputs less power in that region. Owing to a brighter source and increased detector sensitivity, the results of the NIR setup were "easier" to obtain, as the clothing could be illuminated from a distance, while aligning the collecting optics towards the hit point. The MIR setup requires a more precise setting of the sample as it operates in a "focused" mode, which requires to place the piece of textile to be characterized at the optimal working distance. Despite the more challenging aspect of measuring diffuse reflectance in the MIR, the ARCoptix FTMIR provided similar quality results compared to a more traditional NIR setup, offering an extended spectral range for this kind of characterization. .
