Explain polarization by double refraction.
b) Define uniaxial crystal and biaxial crystal.
c) Define Optic axis.
Answers
Answer:
a) When the unpolarized light ray falls on certain crystals like calcite, quartz etc. then it is found that 2 refracted rays are produced. This phenomena is called double refraction.
eg:- Out of 2 refracted ray.
b) Biaxial Crystal
• This crystal is described by two optical axis and three principal refractive indices.
• Examples of biaxial Crystals are mica, lead oxide, topaz etc.
• These crystals are also known as birefringent crystals.
• When light beam passed through this crystal, it splits into two parts. Both the fractions are e-rays. These waves or rays have different directions and speeds.
• Examples: Crystalline structures e.g. orthorhombic or monoclinic or triclinic etc.
Uniaxial Crystal
• This crystal is described by one optical axis and two principal refractive indices.
• Examples of uniaxial Crystals are calcite, KDP, quartz, rutile etc.
• When light beam passes through such crystal, it splits into o-ray and e-ray >>. Here o-ray passes through it without any deviation where as e-ray deviates at air to crystal interface.
• There are two forms of uniaxial crystals viz. positive uniaxial crystal and negative uniaxial crystal.
c) An optical axis is a line along which there is some degree of rotational symmetry in an optical system such as a camera lens or microscope. The optical axis is an imaginary line that defines the path along which light propagates through the system, up to first approximation.
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