Wednesday, 19 April 2017

Sugar sweet colors

The beautiful colors we observe under the polarizing microscope have to do with the "optical activity" of - in this case - fructose.

Light is an electromagnetic wave phenomenon, in which the direction of vibration is perpendicular to the direction of propagation. An electric and a magnetic vector vibrate thereby at right angles relative to each other. In a 'normal' light, such as daylight, all directions of vibration are present at the same time. Polarized light, is light wherein only one direction of vibration in the beam is present.
Polarized light is made by ‘filtering’ a light beam with a polarizing filter whereby only one single direction of vibration remains. Typically, a polarization filter is made up of two glass or plastic plates having a polarizing plastic film in between. Easily said, this film can be compared with louvered blinds. The light can only pass through it in one direction.

The polarized light microscope is designed to observe and photograph specimens that are visible primarily due to their optically anisotropic character. Image contrast arises from the interaction of plane-polarized light with a birefringent (or doubly-refracting) specimen, to produce two individual wave components that are each polarized in mutually perpendicular planes. The velocities of these components, which are termed the ordinary and the extraordinary wave fronts, are different and vary with the propagation direction and the corresponding refractive index through the specimen. This results in different wavelengths of the components. After exiting the specimen, the light components are out of phase, but are recombined with constructive and destructive interference when they pass through the analyzer, resulting in different colors. This effect can be used, for example, for the determination of minerals.

Anisotropy: A material is referred to as anisotropic when its characteristics are not the same in every direction. This concept may relate to different material properties, such as, for example, the refractive index of crystals. When the material properties do not depend on the direction, the material is referred to as isotropic.

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