The mid-IR hyperspectral imager consists of a Michelson interferometer and a Stirling-cooled Focal Plane Array (FPA) Strained Layer Superlattice (SLS) detector. The flat mirror interferometer is actively aligned, and the system is sealed and cooled. The maximum spectral resolution is 1 cm⁻¹, with measurements typically performed at 4 cm⁻¹, in external reflection IR mode, within the spectral range of 4000–800 cm⁻¹. The total size of the FPA detector is 320 × 256 pixels, with each pixel measuring 30 × 30 µm². The field of view (FOV) of a single pixel is approximately 0.52 mrad, corresponding to a lateral resolution better than 1 mm (0.7–0.8 mm) at a working distance of 1 m. For preview mode, which operates like a thermal imaging camera, the full detector size is utilized. For standard measurements, the active detector area is limited to 176 × 176 pixels, covering a measurement area of approximately 11 × 11 cm² at a 1 m working distance. The Noise Equivalent Temperature Difference (NETD) for measurements with 16 co-additions and a 3 × 3 pixel averaging, within the spectral range of 1050 cm⁻¹ to 1150 cm⁻¹, is approximately 90 mK. For reflection mode measurements, the sample is illuminated by an infrared radiation source consisting of a Globar (SiC) light source and a parabolic condenser mirror with a diameter of approximately 30 cm. The Globar is mounted on a motorized actuator that adjusts the working distance of the source from 1 m to infinity in a defocused position. During the data analysis period after each measurement, the actuator automatically moves to defocus the source, or the source can be temporarily turned off to minimize radiation exposure to the sample. The temperature—and thus the radiation spectrum and intensity of the source—can be adjusted by varying the input electrical power. The intensity can also be attenuated with a manually adjustable aperture. The source temperature is measured and monitored by a pyrometer installed at the center of the condenser. The maximum source temperature is 1000 °C. The acquisition time for a complete hyperspectral data cube is 8 minutes (with an integration time of 70 μs and 16 co-additions). Of this, approximately 7 minutes are required to scan the full size of the FPA in 8 blocks of 22 lines (22×176 pixels), and the remaining minute is needed for data saving and FFT processing. The automatic source control enables defocusing during this period. The temperature increase on the painting surface, with a source temperature of 800 °C and an 8-minute acquisition period, is < 6 °C, as measured by an exposure meter (Elsec 775). Reflectance spectra are calculated as the ratio between the sample's reflection and the reflection recorded from a reference target (used as background) that is selected according to the reflectance and emission properties of the investaigated surface. The support by E-RIHS (MUR FOE ERIHS IT and PON Ricerca e Innovazione 2014-2020, CCI: 2014IT16M2OP005) is acknowledged.

Image
Image/RGB
Image/Gray scale
Image/False color
Dataset/2D
Dataset/3D
Dataset/Data package (images, spectra, other)

Noncontact (no physical contact)
Nondestructive (no permanent damage or alteration)
Noninvasive (no physical alteration)

Bruker

upgraded version of the model HI90

macro
10 x 10 cm 2