New instrumental approaches for performing vibrational Raman,
near-infrared and mid-infrared spectroscopic imaging microscopy
are described. The instruments integrate imaging quality filters
such as acousto-optic tunable filters (AOTFs), with visible
charge-coupled device (CCD) and infrared focal-plane array
detectors. These systems are used in conjunction with
infinity-corrected, refractive microscopes for operation in
the visible and near-infrared spectral regions and with
Cassegrainian reflective optics for operation in the mid-infrared
spectral interval. Chemically specific images at moderate spectral
resolution (2 nm) and high spatial resolution (1 μm) can be
collected rapidly and noninvasively. Image data are presented
containing 128 × 128 pixels, although significantly larger
format images can be collected in approximately the same time.
The instruments can be readily configured for both absorption
and reflectance spectroscopies. We present Raman emission images
of polystyrene microspheres and a lipid/amino acid mixture
and near-infrared images of onion epidermis and a hydrated
phospholipid dispersion. Images generated from mid-infrared
spectral data are presented for a KBr disk containing
nonhomogeneous domains of lipid and for 50-μm slices of
monkey cerebellum. These are the first results illustrating
the use of infrared focal-plane array detectors as chemically
specific spectroscopic imaging devices and demonstrating their
application in biomolecular areas. Extensions and future
applications of the various vibrational spectroscopic imaging
techniques are discussed.
High operating temperature pBn barrier mid-wavelength infrared photodetectors and focal plane array based on InAs/InAsSb strained layer superlattices