Linear optical birefringence and dichroism measurement in liquids and colloidal dispersions

An apparatus is described for measuring the linear birefringence and linear dichroism induced in liquids or dispersions by an applied magnetic field. The apparatus uses a vibrating beam phase modulator and conventional optical and electro-optical components. It is capable of measuring Delta n' (the real part of the complex birefringence Delta n) down to about 10-12 and Delta n (the imaginary part of Delta n) down to about 10-10. Results are given for liquids of very small Cotton-Mouton constant, hitherto unmeasurable, and very dilute colloidal dispersions. Dust removal from sample liquids is shown to be of major importance for weakly birefringent or dichroic samples.