Nonachromaticity and reversals of topological phase as a function of wavelength
Achromaticity of the topological phase arising from polarization transformations of light  has been the bas is of several applications . Achromatic retarders based on Paucharatnam’s work are routinely used in Astronomical polarimetry. Using the standard example of the “QHQ retarder”, where Q and H are quarterwave and halfwave retarders, the topological origin of achromaticity was explained in ref.  where it was also shown that at wavelengths far removed from the design wavelength λ0 of the retarder it can show the opposite behaviour i.e. sharp changes and reversals of phase. The new result I wish to report here is that such sharp changes and reversals can in fact. be made to occur at wavelengths arbitrarily close to λ0. This would happen if the retardation of Q and H were equal to (2n+1/2)π and (4n+1)π respectively, where n is an integer which could be made large.
References and links
- 1.S. Pancharatuam, “Genera lized theory of interference and its applications”, Proc. Indian. Acad. Sci. A 44, 247 (1956).Google Scholar