Polarization rotator, Fresnel rhomb

Thus, the polarization of both the incident and scattered light must be controlled. A typical argon laser produces linearly polarized light. The incident polarization can be adjusted to be either vertical or horizontal with respect to the scattering plane with a double Fresnel rhomb polarization rotator. The scattered light can be analyzed with a Glan-Thomp-son prism polarizer. 

The experimental apparatus is depicted in Fig. 3 and is described in detail elsewhere [14]. It consists of a molecular beam scattering chamber, pulsed frequency-doubled dye laser, double fresnel rhomb polarization rotator, fibre bundles to coUect fluorescence from excited states, and time-gated photon counting and boxcar averaging equipment. 

Cotton also investigated the use of ellipticity measurements for CD studies. The combination of a linear polarizer and a Fresnel rhomb was used by Cotton to produce polarized light which could vary in its orientation from circular to elliptical. A second linear polarizer was then used to monitor changes in the orientation of the major axis of the ellipse which occurs as a result of the CD. In addition, the apparatus could also be used to measure optical rotation (circular birefringence). The experimental simplicity of this approach relative to his other system allowed more sensitive measurements to be made. This experimental simplicity also served as an impetus for other researchers in the field, and the ellipticity approach dominated the available technology from the time of Cotton s first efforts to the 1960 s, when electronically modulated systems were developed. 

The rotation of the linear polarizer 45°, to the appropriate Fresnel rhomb axis, induces the generation of left or right polarized light. 

Optical retarder plates, of appropriate thicknesses, made of birefrin-gent material, normally crystalline quartz or mica, can be used to rotate the plane of polarization for linearly polarized light or to produce circularly polarized light. To rotate linearly polarized light by an arbitrary angle, a double Fresnel rhomb is very useful (Fig.6.46). 

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