Calibration Procedure for Attenuation Coefficient Measurements in Highly Opaque Media Using Infrared Focal Plane Array (IRFPA) Spectroscopy

Abstract

The purpose of this article is to present a new calibration procedure for spectroscopic measurements using an infrared focal plane array (IRFPA) spectrometer on highly opaque middle-wave infrared (MWIR) media. The procedure is based on the properties of the IRFPA camera and especially the integration time (IT), which is the main parameter that can be adjusted to control the sensitivity of the measurements. The goal of the paper is to experimentally validate this dependence with the direct reference intensity light coming out of the IR monochromator in order to predict the spectrum shape and intensity level in a range out of the camera saturation. This method allows determining spectrum used as background for transmittance calculation. It has been applied in the case of measurement of water transmittance, which is a highly opaque medium and whose measurement requires high ITs. The main result is the ability to take an IR spectroscopic imaging measurement through 300 µm of water and the determination of its transmittance with sufficient sensitivity due to the proposed calibration procedure. This procedure allows the possibility of transitory studies in heterogeneous aqueous media.

3D infrared thermospectroscopic imaging

“…Here, on the basis of the fastest spectroscopy systems proposed by Süss et al 23 , the system offered by Süss et al allows 76,923 scan/s with a monosensor, which is on average already 1000 times faster than conventional systems. Thus, a classic small-format IR camera can acquire 1 image of 320 × 256, i.e., 81,920 pixels, in 100 μs, as presented in 8 . The wavelength scanning of the monochromator in the 1.5 to 5.5 μm range is performed at a speed of 0.5 wavelength/s, or within approximately 3 min, to create the full spectrum.…”

“…Following the methodology described in previous papers 8,24 , the acquired signal S from the contributions of two distinct signals is given by:…”

“…For years, Raman, infrared, near-infrared (NIR) 2 and infrared spectroscopy 3 imaging techniques have been used for the purpose of analysis of chemical compounds in solids, liquids or gases, either in reflection or transmission mode. Although NIR spectroscopy or monosensor infrared spectroscopy leads to chemical analysis in liquids or gases [4][5][6] , few studies exploited the potential of the imaging techniques in the MWIR region [7][8][9] for solid materials. The current imaging techniques are predominantly based on spatial scanning with a monosensor, and the application domains are mainly found in biology and chemistry.…”

Thin Coatings of Cerium Oxide Nanoparticles with Anti-Reflective Properties

“…Transmission in the mid-IR range was measured on a specific system, namely fast infrared imaging spectroscopy (FIIST [33,34]), which permits us to image the optical transmission in the range of 2-6 µm.…”

“…with R is the reflectance at the different interfaces where subscripts A, C, and S stand for air, coating, and substrate respectively, α = 4πk 3 /λ is the extinction coefficient in the substrate with k 3 as the imaginary part of the refractive index of the substrate of thickness L. R ACS and R SAC are calculated following the procedure of Equation (1); in the case of a bare substrate, replace R ACS and R SCA with R AS . We measured the transmission T of a two-sided polished substrate coated with a micro-structured pattern using a spectro-imaging set-up (described in Section 4.4 and in [33,34]). Owing to the imaging capability of the device, it is possible to select the measurement place in a heterogeneous sample such as ours, see Figure 6A with a spatial resolution of about 25 µm in this specific case, but which depends on the magnification.…”