Wide-field mid-infrared hyperspectral imaging of adhesives using a bolometer camera

Abstract

By combining a bolometer detector with an imaging-type interferometer, an inexpensive, easy-to-handle wide-field mid-infrared hyperspectral imaging apparatus was produced. We measured the distributions of four types of thin adhesive layers on an aluminium plate and analysed the results using correlation coefficients to visualise the distribution of various adhesives that cannot be discerned by the naked eye or conventional methods such as visible/near-infrared spectroscopic/fluorescent photography. The measurement wavelength range, obtained spectrum’s wavenumber resolution, and measurement time was 8–14 μm, about 9 cm−1, and about 30 s, respectively. Using conventional methods, adhesives could not be distinguished from the others. By using this method, we found that adhesives could be precisely distinguished by setting an appropriate threshold value for the correlation coefficient. Thus, our approach can accurately measure the spatial distribution of different types of adhesive that cannot be discriminated by conventional methods.

Infrared Spectroscopic Imaging Advances as an Analytical Technology for Biomedical Sciences

“…31 The increased speed can be used to scan much larger areas such as large polymer samples, pharmaceutical tablets, or forensic scenes and pieces of evidence. 156–160 An example of the DF potential in visualizing crystallization patterns of a polyethylene glycol (PEG) polymer over a large spatial region is shown in Figure 7. As can be seen (left panel), a ratio of just two frequencies (1415:1410 cm −1 ) was enough to visualize the spherulite structure present in the PEG sample in just 9 min.…”

“…The scanning speed increase of a QCL microscope in a wide field configuration can reach a factor of 1000 per essential frequency as compared to an FT-IR system, while for a QCL point system, a factor of 180 was recently reported . The increased speed can be used to scan much larger areas such as large polymer samples, pharmaceutical tablets, or forensic scenes and pieces of evidence. − An example of the DF potential in visualizing crystallization patterns of a polyethylene glycol (PEG) polymer over a large spatial region is shown in Figure . As can be seen (left panel), a ratio of just two frequencies (1415:1410 cm –1 ) was enough to visualize the spherulite structure present in the PEG sample in just 9 min.…”

Preliminary measurements of oil paint on paper using a mid-infrared hyperspectral imaging system with a bolometer camera and image interferometer.

“…Statistical analysis of the spectral groups can visualize differences in materials in the sample invisible to the naked eye. HSI is used in various elds [1][2][3][4][5][6][7][8][9][10][11] ; for example, Sugawara et al have studied applications such as inspecting document materials in forensic science and measuring paintings in cultural heritage science [12][13][14][15][16][17][18][19][20][21] . HSI techniques include visible (0.4-0.7 µm), near-infrared, mid-infrared, and far-infrared HSI, depending on the wavelength of light used.…”

Spectral imaging at high definition and high speed in the mid-infrared

“…When realized in the mid-infrared (MIR) spectral region, spectral imaging allows direct spatial differentiation of chemical composition, providing an indispensable tool for many applications in chemical, medical, and bio-related fields. MIR spectral imaging has been used to great effect in label-free histopathological imaging (1,2), standoff detection of materials (3)(4)(5)(6), gas analysis (7), and environmental surveying (8). However, a broader utilization of the technique for applications that require both highspeed and high-definition imaging capabilities has remained challenging.…”