MULTIPLE REFLECTIONS IN AN OPTICAL RETARDER INVESTIGATED BY SPECTROSCOPIC TRANSMISSION ELLIPSOMETRY

The response ofthe ellipsometric parameters as a function of wavelength has been derived for an optical retarder. Experimental results in the wavelength region 400-1000 nm are given, these are in agreement with the derived formalism. The theory of multiple reflections in an isotropic medium and the optics of retarders have been described in the previous literature. Holmes [1] described multiple reflection in a quarter wave plate, an anisotropic medium. The theory is illustrated with model calculations, where the thickness of the retarder is the variable. Automatized spectroscopic transmission ellipsometry however gives the opportunity to perform measurements which show the multiple reflection in a retarder as a function of wavelength. The complex relative amplitude transmission coefficient of a wave plate can be defined as r =tan y/exp(iA) , (1) where tan ~ and A are the relative amplitude transmission coefficient and the relative phase shift at trans-mission respectively. For a single transmission A is given by A = (~o-~e) =2ted (no-ne) /2, (2) where ~ is the phase shift and n the refraction index, the subscripts o and e refer to the ordinary and extra ordinary beam, d is the thickness of the transmission element and 2 the applied wavelength. The absorption along the two axes of the retarder is assumed to be equal, therefore q/should be re/4. However as describe