Browse Prior Art Database

Linear Retarder

IP.com Disclosure Number: IPCOM000085335D
Original Publication Date: 1976-Mar-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Kenyon, DM: AUTHOR [+3]

Abstract

A linear retarder is described with approximately one-quarter wavelength phase retardation over the wavelength range 250 to 900 nm which may be used in an ellipsometer. Present retarders are made of silica which introduces phase and azimuth errors due to strain.

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Linear Retarder

A linear retarder is described with approximately one-quarter wavelength phase retardation over the wavelength range 250 to 900 nm which may be used in an ellipsometer. Present retarders are made of silica which introduces phase and azimuth errors due to strain.

Fig. 1 shows a general arrangement of reflectors M, for an odd number of reflections. Reflectors M are rigidly mounted in a tube fitted with windows at each end. The windows may be removed and replaced in precisely the same orientation with their strain axes parallel to an axis of the retarder. The resulting enclosure is filled with liquid having a high-refractive index. An expansion chamber is connected to the tube to avoid strain in the windows due to thermal expansion of the liquid. Fig. 2 shows an alternative general arrangement of reflectors M for an even number of reflections.

In Fig. 1 total internal reflections occur at liquid-solid interface, so birefringence is eliminated. The liquid must have a high-refractive index, e.g., tetraethythiosilane (C(2)H(5)S)(4) Si, or water saturated with alkali or alkaline earth halides LiF, NaI, CaCl(2). In the range 400 to 900 nm liquids such as CS(2) or 2-methylbenzophenone are suitable.

The solid reflector M must be of low refractive index, e.g., magnesium fluoride and may be used as a layer evaporated onto a polished silica substrate. An achromatizing layer, e.g., SiO(2) having a refractive index intermediate between the liquid and reflecting...