Once a laser illuminates on a specimen, photons of the laser beam will be absorbed by the sample and pumped to virtual states; it then reemits photons with same or slightly higher/lower frequencies and jump back to ground state. If the frequency is same, it is a Rayleigh scattering process. If the frequency is lower, it is called stock shift; otherwise it is an anti-stock shift. The frequency changes is related to the molecular vibration, rotation, bending. Therefore, similar as IR spectroscopy, Raman can also be adopted as a powerful tool to study the molecular structures.
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Refractive index measurement by Abbe Refractometer
Abbe refractometer measures a material’s refractive index through determining the critical angle αc under total internal reflection conditions.
Continue reading “Refractive index measurement by Abbe Refractometer”Numerical aperture and resolution
The numerical aperture of a microscope objective is the measure of its ability to gather light and to resolve fine specimen detail while working at a fixed object (or specimen) distance. Resolution of an optical microscope is defined as the smallest distance between two points on a specimen that can still be distinguished as two separate entities.
Continue reading “Numerical aperture and resolution”Yellowness index measurement
Yellowness Index (YI) is a number calculated from spectrophotometric data to characterize the change in color of specimen from clear or white to yellow.
Continue reading “Yellowness index measurement”Study of sub-surface features by laser confocal microscopy
A laser confocal microscope has the ability to isolate a single plane of focus from thick samples or overlapping objects. Therefore it is a powerful tool to image the surface or bulk (in transparent media) features of a specimen.
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