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Gout and pseudogout crystals viewed under a microscope with a red compensator, which slows red light in one orientation (labeled "polarized light axis"). [18] Urate crystals ( left image) in gout appear yellow when their long axis is parallel to the slow transmission axis of the red compensator and appear blue when perpendicular.
The direction of the electric field determines the polarization of light, and crystals will respond in different ways if this angle is changed. These kinds of crystals have one or two optical axes. If absorption of light varies with the angle relative to the optical axis in a crystal then pleochroism results. [4]
The two asymmetric crystal forms, dextrorotatory and levorotatory, of tartaric acid. Sucrose solution concentration measuring experiment, demonstrating optical rotation. The rotation of the orientation of linearly polarized light was first observed in 1811 in quartz by French physicist François Arago. [7]
Polarized light microscopy can mean any of a number of optical microscopy techniques involving polarized light. Simple techniques include illumination of the sample with polarized light. Directly transmitted light can, optionally, be blocked with a polariser oriented at 90 degrees to the illumination. More complex microscopy techniques which ...
Extinction is a term used in optical mineralogy and petrology, which describes when cross-polarized light dims, as viewed through a thin section of a mineral in a petrographic microscope. Isotropic minerals, opaque (metallic) minerals, and amorphous materials (glass) do not allow light transmission under cross-polarized light (i.e. constant ...
Under the microscope the spherulites are of circular outline and are composed of thin divergent fibers that are crystalline as verified with polarized light. Between crossed Nicols, a black cross appears in the spherulite; its axes are usually perpendicular to one another and parallel to the crosshairs; as the microscope stage is rotated the cross remains steady; between the black arms there ...
Tension lines in a plastic protractor seen under cross-polarized light The experimental procedure relies on the property of birefringence , as exhibited by certain transparent materials. Birefringence is a phenomenon in which a ray of light passing through a given material experiences two refractive indices .
As polarised light passes through a birefringent sample, the phase difference between the fast and slow directions varies with the thickness, and wavelength of light used. The optical path difference (o.p.d.) is defined as o . p . d . = Δ n ⋅ t {\displaystyle {o.p.d.}=\Delta \,n\cdot t} , where t is the thickness of the sample.