Transmitted and Reflected Circularly Polarized Light Microscopy: Origins, Developments and Applications with a White Light Source
THE MICROSCOPE
2013, Volume 61:1, pp. 3–13
DOI
https://doi.org/10.59082/TTON2285
AUTHORS
Franz W. Nentwich
ABSTRACT
Circularly polarized and circularly analyzed light for microscopy with a white light source remains underutilized, even though circular polariscopes using this same kind of illumination date back to the early 1800s. Possible reasons for this delay in application to microscopes are as follows: an emphasis on microscopes with linear polarizers and analyzers, spurious interference colors associated with early chromatic quarter-wave plates, significant applications that did not develop until the late 1800s, and problems with the earliest quarter-wave rhombs. Fresnel rhombs in the earliest polariscopes deflected the beam laterally, restricted the field of view, and caused large retardation errors for obliquely incident rays. By contrast, the Mooney rhomb, which was not invented until 1952, would, with dielectric films on its faces, produce much smaller retardation errors, and in an inverted microscope such a rhomb would doubly serve to deflect the beam to a convenient viewing angle. In an upright microscope, an inline prism known as a modified AD-1 device could provide highly broadband circularly polarized light if combined with an achromatic quarter-wave plate in the accessory slot. Both transmitted and reflected circularly polarized light is possible with these optical elements, providing many applications for photomicrography and image analysis.