In a study of the Sénarmont compensator method of flow birefringence measurement, the effects of polychromatism and of error in the quarter-wave plate are investigated by a theoretical treatment of the behavior of the cross of isocline. It is found that with monochromatic light an error in the quarter-wave plate introduces asymmetry into the scissors-type motion of the cross of isocline. The arms of the cross do not close completely. Rather, one arm disappears while the other continues its motion toward the 45° position in the annulus. It is shown by example that, with the proper quarter-wave plate, polychromatic light from a filter can give a result which is almost the same as that given by monochromatic light and a quarter-wave plate without error. A mismatch of the quarter-wave plate and polychromatic light gives essentially the same error in the measurement of birefringence as the error caused by a comparable mismatch between the quarter-wave plate and monochromatic light.
© 1964 Optical Society of America
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