Abstract

A major limiting factor in polarized light microscopes is stray light caused by rotation of the state of polarization at oblique lens surfaces. The pupil function for such a system is a dark cross, and the point spread function resembles a four-leaf clover rather than an Airy disk.¹ Reducing the numerical aperture of the condenser and/or objective avoids high obliquity surfaces but also reduces resolution. Polarization rectifiers, which introduce compensating amounts of rotation, have been difficult to produce. Recently, it has been found that operating the microscope with high compensator settings (bias retardation) and video image enhancement effectively corrects the polarization anomaly, permitting operation at full aperture with high contrast.² This work explores the theoretical basis of the anomaly correction and investigates the fundamental limits of the method. Mathematical models developed for the pupil and point spread functions elucidate the means by which bias retardation and video enhancement restore nearly diffraction-limited performance. Images obtained from the microscope confirm the theoretical predictions. At high (quarter wave) bias retardations, the pupil function is nearly uniform, and the point spread function approaches an Airy disk, but both remain slightly asymmetric, and the phase error in the pupil displays a residual astigmatism.

© 1985 Optical Society of America