Photovoltaics Photovoltaic devices can be characterized by global hyperspectral imaging by
electroluminescence (EL) and
photoluminescence (PL) mapping. This technique allows the characterization of different aspects of
photovoltaic cells :
open circuit voltage, transport mechanisms,
external quantum efficiency,
saturation currents, composition map, uniformity components, crystallographic domains, stress shifts and lifetime measurement for material quality. It has in fact already been employed for the characterization of
Cu(In,Ga)Se2 (CIGS) and
GaAs For example, it has been used for the early diagnosis of retina anomalies (e.g.:
age-related macular degeneration (AMD), retinal vessel oxygen saturation ), in the
biomedical field in addition to
neurology and dermatology for the identification and location of certain proteins (e.g.:
hemoglobin) or pigments (e.g.:
melanin). In life science, this technique is used for darkfield and epifluorescence microscopy. Several studies showed hyperspectral imaging results of gold
nanoparticles (AuNPs) targeting
CD44+ cancer cells and
quantum dots (QDs) for the investigation of molecular dynamics in the
central nervous system (CNS). Moreover, hyperspectral imaging optimized in the near-infrared is a well-suited tool to study single carbon nanotube photoluminescence in living
cells and tissues. In a Scientific Reports paper, Roxbury et al. presents simultaneous imaging of 17 nanotube
chiralities, including 12 distinct
fluorescent species within living cells. The measurements were performed
ex vivo and
in vivo.
Semiconductors After the invention of the
transistor in 1947, the research on semiconductor materials took a big step forward. One technique that emerged from this consists of combining
Raman spectroscopy with hyperspectral imaging which permits characterization of samples due to Raman diffusion specificity. For example, it is possible to detect
stress, strain and
impurities in
silicon (Si) samples based on frequency, intensity, shape and width variation in the Si
phonon band (~520 cm−1). Generally, it is possible to assess material's
crystalline quality, local stress/strain,
dopant and impurity levels and surface temperature.
Nanomaterials Nanomaterials have recently raised a huge interest in the field of material science because of their colossal collection of industrial, biomedical and electronic applications. Global hyperspectral imaging combined with
photoluminescence,
electroluminescence or
Raman spectroscopy offers a way to analyze those emerging materials. It can provide mapping of samples containing
quantum dots,
nanowires,
nanoparticles, nanotracers, etc. Global hyperspectral imaging can also be used to study the diameter and
chirality distribution and radial breathing modes (RBM) of
carbon nanotubes. It can deliver maps of the uniformity, defects and disorder while providing information on the number and relative orientation of layers, strain, and electronic excitations. It can hence be employed for the characterization of
2D materials such as
graphene and
molybdenum disulfide (MoS2).
Industrial Hyperspectral imaging allows extracting information on the composition and the distribution of specific compounds. Those properties make hyperspectral imaging a well-suited technique for the
mining industry. Taking advantage of the specific spectral signature of minerals Photonic Knowledge's Core Mapper™ offers instant mineral identification. This technology delivers
monochromatic images and fast
mineralogy mapping. The wide-field modality renders possible the identification of mineral signatures but also the classification of
plants (e.g.:
weeds,
precision agriculture) and
food (e.g.:
meat freshness,
fruit defects) and can be used for various outdoor applications. Being able to quickly and efficiently detect explosive liquid
precursors represents an important asset to identify potential threats. An hyperspectral camera in the SWIR region allows such detection by acquiring rapidly spectrally resolved images. The monochromatic full-frame images obtained permit fast identification of
chemical compounds. Detection of
sulfur by
laser-induced breakdown spectroscopy (LIBS) can also be easily achieved with holographic Bragg grating used as filtering elements.
Instrument Calibration and Characterization The
calibration of measuring instruments (e.g. :
photodetector,
spectrometer) is essential if researchers want to be able to compare their results with those of different research groups and if we want to maintain high standards. Spectral calibration is often needed and requires a well-known source that can cover a wide part of the electromagnetic spectrum.
Tunable laser sources possess all of the above requirements and are hence particularly appropriate for this type of calibration. Before the
Gemini Planet Imager (GPI) was sent to Gemini South, it was necessary to calibrate its
coronagraph. For this matter, a nearly achromatic and collimated source that could cover 0.95-2.4 μm was needed. Photon etc.'s efficient tunable laser source was chosen to test the coronagraph. The tunable source was able to provide an output across the whole GPI wavelength domain.
Thin-film filters are necessary elements in optical instrumentation.
Band-pass,
notch and edge filters now possess challenging specifications that are sometimes strenuous to characterize. Indeed, an
optical density (OD) higher than 6 is difficult to identify. This is why a group of researchers from Aix Marseille Université developed a spectrally resolved characterization technique based on a supercontinuum source and a laser line tunable filter. The method is described in detail in the Liukaityte et al. paper from Optics Letter and allowed to study thin-film filters with optical densities from 0 to 12 in a wavelength range between 400 nm and 1000 nm. ==References==