Simple technique for determining the wave plate's fast axis and retardance

FRANCISCO E. VEIRAS; MARÍA T. GAREA; LILIANA I. PEREZ

Porto

Congreso; 8th Ibero American Optics Meeting/11th Latin American Meeting on Optics, Lasers, and Applications.; 2013

SPOF

Linear retarders, such as wave plates, introduce a phase shift between two privileged components of linear polarized light. Commercial wave plates or other linear retarders, as well as ad-hoc built prototypes, may have an incomplete specifications data sheet for a particular application. For example, their behavior might not be specified for a different wavelength, and/or the fast and slow axis marks may be missing. Basic operation of linear retarders on most classic techniques relies on the knowledge of these characteristics. They are of great interest for ellipsometry and for accurate polarization control. It is known that the retardance introduced between two orthogonal components of the electric field varies when a wave plate is rotated against a monochromatic light source. Such variations depend on the azimuth angle and allow the introduction of phase shifts between the branches of a polarization interferometer, which may consist only of a uniaxial crystal slab and two polarizer sheets. As a result, the fringe pattern collected is phase modulated according to the retardance introduced. The fringe movement allows the identification of both the fast and the slow axis, and the determination of the retardance introduced. In this work we show how it is possible to characterize a retarder under study at a given wavelength by means of a laser source, a uniaxial crystal, polarizer sheets and a CCD.