Half wave plate achromatic

Retardation plates are frequently used in polarimetry instruments. Quarter-wave and half wave plates are most often used and may be fabricated in either wavelength-dependent or achromatic forms. 

Achromatic half-wave plates can be easily made from the combination of two quarter-wave Fresnel rhombs shown in Figure 9.3b. This geometry has the nice feature of removing the translation of the light beam that is associated with a single rhomb. 

FIGURE 45.9 Schematic of a confocal LIP detection system with source, optics, and detector shown. The optics include mirrors (M), laser line filter (LF), half-wave plate (X/2), polarizer (pol), dichroic beamsplitter (DB), microscope objective (MO), pinhole (ph), filter, and achromat lenses (achr). The source shown is an argon ion laser, and the detector is an avalanche photodiode (APD). While the electrophoresis channel shown here is in a capillary (CE), the system could be readily applied to a microchip. (Reprinted from Johnson, M.E. and Landers, J.P., Electrophoresis, 25, 3515, 2004. With permission.)... 

Figure 8.2 depicts the normalized light transmittance TV) of the 90° TN cell at three primary wavelengths R = 650, G = 550, and B = 450 nm. Since the human eye is most sensitive at green, we normally optimize the cell design at i = 550 nm. From Equation (8.4), the first 71 = 1 occurs at dAn 480 nm. The color dispersion (i.e. the wavelength dependency of the light transmittance) at = 0 is not too sensitive to dAnIX beyond the first minimum. Therefore, the TN cell can be treated as an achromatic half-wave plate. The response time depends on the cell gap and... 

Polarization imaging capability. A warm half-wave plate which is achromatic from 1-2.5 (jcm is mounted in a rotating assembly above the camera window and is used in combination with a fixed cold smalyzer inside the dewar for polarization imaging programs. Images taken with the wave plate at four positions will be combined to determine linear polarization. 

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