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.
C. A. HOLLINGSWORTH, W. E. KAISER, and W. T. GRANQUIST, "Theory of Measurement of Flow Birefringence by Use of the Sénarmont Compensator. II. Effect of Quarter–Wave Plate Error and Polychromatism," J. Opt. Soc. Am. 54, 633-637 (1964)