Biomedical Engineering Reference
In-Depth Information
Fig. 8.3
Schematic of a home-built angle-resolved optical spectroscopy at Fudan University. The
light source is a Xenon lamp which covers a wavelength range from 250 to 800 nm. Diaphragms are
used to control the beam size. A beamsplitter is used to split light beams (50R/50T). Two coaxial
motorized rotary stages are used to control the incident and detecting angles. The rotating angles
of the upper (
dark gray disk
)andlower(
light gray disk
) stages can be adjusted independently.
Samples are placed on the center of the upper stage. An optical fiber is put on the detection arm
which is fixed on the lower stage. A high-resolution spectrometer is connected to the fiber. Two
Glan-Tailor polarizers can be added in if measurements with polarized light are needed
In this angle-resolved spectrometer, the incident angle
can be adjusted by
rotating the detection arm fixed on the lower stage. Different spectra such as
specular reflection (incidence at
and detection at
), scattering (incidence at
and detection at other angles), backscattering (incidence and detection at the same
), and transmission can be obtained. Two polarizers can be added in if polarized
spectra are to be measured. In measurements of absolute reflectance, a reference
standard, e.g., diffuse white, should be used in order to remove the influence of the
characteristic wavelength dependence of light sources.
Structurally colored parts of biological samples, e.g., scales of insects and
barbules of bird feathers, are usually very small. A single part may even display
different structural colors. Under the circumstances, microscopic spectral detections
are necessary. A typical microspectrometer that can detect spectra of microscopic
regions is schematically shown in Fig.
8.4
.
Total reflection, transmission, and absorption spectra can provide important
information for structural colors, which can be measured with integrating spheres, as
shown in Fig.
8.5
. An integrating sphere is a hollow spherical cavity with a diffuse
high reflectivity coating on its inner surface, and also with small holes for light
entrance and exit. Samples are placed in close proximity to the exit port. Incident
light can be introduced, e.g., through an optical fiber. It will bounce around the inner
surface and finally impinge the detector.
