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Spectral imaging has many applications, from methane detection using satellites to disease detection on crops. However, spectral cameras remain a costly solution ranging from 10 thousand to 100 thousand euros for the hardware alone. Here, we present a low-cost multispectral camera (LC-MSC) with 64 LEDs in eight different colors and a monochrome camera with a hardware cost of 340 euros. Our prototype reproduces spectra accurately when compared to a reference spectrometer to within the spectral width of the LEDs used and the ±1 σ variation over the surface of ceramic reference tiles. The mean absolute difference in reflectance is an overestimate of 0.03 for the LC-MSC as compared to a spectrometer, due to the spectral shape of the tiles. In environmental light levels of 0.5 W m−2 (bright artificial indoor lighting) our approach shows an increase in noise, but still faithfully reproduces discrete reflectance spectra over 400 nm–1000 nm. Our approach is limited in its application by LED bandwidth and availability of specific LED wavelengths. However, unlike with conventional spectral cameras, the pixel pitch of the camera itself is not limited, providing higher image resolution than typical high-end multi- and hyperspectral cameras. For sample conditions where LED illumination bands provide suitable spectral information, our LC-MSC is an interesting low-cost alternative approach to spectral imaging. [ABSTRACT FROM AUTHOR]

We report on a two-color mid-infrared pump-probe spectroscopic study of the dynamics of the OH stretch vibrations of HDO molecules dissolved in a concentrated (10 M) solution of NaOD in D[sub 2]O. We observe that spectral holes can be created in the broad OH stretch absorption band that change neither position nor width on a picosecond time scale. This behavior differs strongly from that of pure HDO:D[sub 2]O where rapid spectral diffusion (τ[sub c]≈ 600 fs) occurs. The long-living inhomogeneity indicates that a concentrated aqueous NaOX (X=H,D) solution has a very static hydrogen-bond network. The results also show that the absorption band of the OH stretch vibration consists of two separate classes of OH groups with very different vibrational lifetimes. For component I, the lifetime of the OH stretch vibration is ∼600 fs and increases with OH frequency, which can be explained from the accompanying decrease in the strength of the hydrogen-bond interaction. This component represents HDO molecules of which the OH group is bonded to a D[sub 2]O molecule via a DO-H···OD[sub 2] hydrogen bond. For component II, the lifetime is ∼160 fs, and does not show a significant frequency dependence. This component represents HDO molecules that are hydrogen bonded to a D[sub 2]O molecule or an OD[sup -] ion. The short, frequency-independent vibrational lifetime of component II can be explained from the participation of the HDO molecule and its hydrogen-bonded partner in deuteron and/or proton-transfer processes. [ABSTRACT FROM AUTHOR]