Waveplate

A waveplate or retarder is an <a href="/facts/Optics/p0vq4S1T">optical</a> device that alters the <a href="/facts/Polarization_(waves)/fP33m0eD">polarization</a> state of a <a href="/facts/Light/jeofpMn4">light</a> wave travelling through it. Two common types of waveplates are the half-wave plate, which rotates the polarization direction of <a href="/facts/Linear_polarization/y4nJQKS1">linearly polarized</a> light, and the quarter-wave plate, which converts between different elliptical polarizations (such as the special case of converting from linearly polarized light to <a href="/facts/Circular_polarization/fYQvT0mI">circularly polarized</a> light and vice versa.)
Waveplates are constructed out of a <a href="/facts/Birefringence/J4lLuR3a">birefringent</a> material (such as <a href="/facts/Quartz/4n86tE2G">quartz</a> or <a href="/facts/Mica/ag4cdnsb">mica</a>, or even plastic), for which the <a href="/facts/Index_of_refraction/yjkzvgeE">index of refraction</a> is different for light linearly polarized along one or the other of two certain perpendicular crystal axes. The behavior of a waveplate (that is, whether it is a half-wave plate, a quarter-wave plate, etc.) depends on the thickness of the crystal, the <a href="/facts/Wavelength/kcJU0ymz">wavelength</a> of light, and the variation of the index of refraction. By appropriate choice of the relationship between these parameters, it is possible to introduce a controlled phase shift between the two polarization components of a light wave, thereby altering its polarization. With an engineered combination of two birefringent materials, an achromatic waveplate can be manufactured such that the spectral response of its phase retardance can be nearly flat.
A common use of waveplates—particularly the sensitive-tint (full-wave) and quarter-wave plates—is in <a href="/facts/Optical_mineralogy/yxkIAoRw">optical mineralogy</a>. Addition of plates between the <a href="/facts/Polarizer/kPDwyboP">polarizers</a> of a <a href="/facts/Petrographic_microscope/A0LTduGv">petrographic microscope</a> makes the optical identification of <a href="/facts/Mineral/LkUFbNmv">minerals</a> in <a href="/facts/Thin_section/FygaCHxS">thin sections</a> of <a href="/facts/Rock_(geology)/FXCJkmop">rocks</a> easier, in particular by allowing deduction of the shape and orientation of the <a href="/facts/Optical_indicatrix/xbmP4Yfy">optical indicatrices</a> within the visible crystal sections. This alignment can allow discrimination between minerals which otherwise appear very similar in plane polarized and cross polarized light.

Waveplate open-in-new

Waveplate