Sensitive Instrument for the Study of Circular Polarization of Luminescence

A sensitive instrument is described for the measurement of the extent of circular polarization of light emitted by chiral molecules. In this instrument the intensity of the circularly polarized component of the luminescence light is selectively modulated by an electro-optic or photoelastic light modulator, while the unpolarized component of the luminescence is unaffected. The modulated light beam is detected by a photomultiplier and the ac component of the electric signal produced is amplified by a phase-sensitive amplifier tuned to the modulation frequency. The light used for the excitation of the sample and the luminescence light are monochromated. An accessory is described which produces controlled mixtures of unpolarized and circularly polarized light and thus permits calibration of the output of the instrument in terms of the degree of circular polarization of the light under examination. Signal to noise ratios of 20 have been readily obtained with luminescence which is circularly polarized to an extent of 10−3 to 10−4.

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