Ay105: lab 2, polarization!dmawet/teaching/... · Light is a transverse electromagnetic wave •...
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Transcript of Ay105: lab 2, polarization!dmawet/teaching/... · Light is a transverse electromagnetic wave •...
Ay105: lab 2, polarization!
Light is a transverse electromagnetic wave
• Solution to the Maxwell equations • Propagation in the z direction • Direction of electric field = direction of polarization
Linearly polarized light
• E0x = 0 => vertically polarized light
Natural light = unpolarized light
Natural light =
incoherent superposition of equally probable polarization states
Natural light (unpolarized) Linear polarizer
Absorb 1 polarization direction let the other one through
(<50% transmission for Natural light)
• I = I0 cos2 θ
• Trigonometric identities, square, sum
• Equation of an ellipse
ε = π/2 (quarter wave) => circular polarization
• Equation of a circle
Birefringence is the optical property of a material having a refractive index that depends on the polarization and propagation direction of light. These optically anisotropic materials are said to be birefringent (or birefractive). The birefringence is often quantified as the maximum difference between refractive indices exhibited by the material. Crystals with asymmetric crystal structures are often birefringent, as are plastics under mechanical stress.
Halfwave vs Quarterwave plate
Stokes vector and Mueller matrices
Stokes vector intuitive view
Stokes vector e-field relationship
• Traditional Stokes vectors and Mueller matrices cannot describe interference effects. The phase information does matter => Jones calculus
• Drawback: Jones calculus cannot describe depolarization, or partial polarization phenomenon, assumes light is 100% polarized
Polarization in astronomy: identify asymmetries
Stars, brown dwarfs, planets SuperNovae
Off to the lab!