Quantitative studies on the polarization optical properties of living cells. I. Microphotometric birefringence detection system.

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Abstract
A method of polarization optical analysis is described in which phase retardation attributable to birefringence of a minute area in a microscopic object is determined. The optical system consists of a polarizing microscope with "rectified" strain-free lenses, a photoelectric detector to determine the intensity of the light passing through a minute window located at the image plane of the specimen, and a stage that moves the specimen at appropriate velocities for scanning. The error resulting from any flare of light emerging from outside of the area to be measured is minimized by limiting the illuminated area. The specimen can be observed during the measurement of light intensity by illuminating the whole microscope field at a wavelength different from that of the light used for the measurement. The retardation of the specimen is determined by comparing the specimen and background intensities as functions of the azimuth of a Brace-Köherl compensator. Alternatively, retardation is obtained directly from the light intensity at a fixed compensator angle, using the theory of polarization optics. The basal noise level for the present apparatus is approximately 0.03 nm when measuring birefringence of a 4-micron2 area in 0.1 s, using a X 40, NA 0.65 objective. The noise decreases in inverse proportion to the square root of the area times the duration of measurement.