Design of an achromatic 1/4 wavelength retarder

In many optical experimental systems, an achromatic 1/4 wavelength retarder is needed to satisfy experiment condition. This can be fulfilled using a rhomb prism which has a nearly constant refractive index in the working wavelength range. To make the easy use of the prism in the optical system and to avoid the problem of central beam deviation, one type of the prism having three total internal reflection faces can be designed to have the total retarding angle equal to 90 degrees. Though the angle can be relatively easily calculated in principle, the size and optical opening window of the prism depend on the practical and optimum geometric design. In this paper, we give a few examples of geometric design by taking different size parameters into consideration. We have made the prisms and put them into the application of measuring the magneto- optical Kerr ellipticity with success. Detailed calculation and error reduction in the design are also given.