Polarization 1 1 1
XY – Plane: Plane of polarisation
S =(E x B)/μo
Unpolarized light Polaroid: Transmits along the pass axis and absorbs along the perpendicular axis
Malus law
Unpolarized light
Degree of polarisation If the incident light is a mixture of unpolarised light of intensity Iu and polarised light of intensity Ip, then the transmitted light is given by:
Polarisation by scattering
Rayleigh scattering Blue sky Red Sunset / Sunrise
Convention
Plane of polarisation is same as plane of incidence Plane of polarisation is perpendicular to the plane of incidence
Polarisation by reflection
unpolarised polarised Brewster angle unpolarised polarised linearly polarised partially polarised Glass
Brewster angle
Brewster’s law = Brewster angle
Polarisation by reflection
Calcite Polarisation by double refraction Quartz - Two refracted beams emerge instead of one - Two images instead of one Optic Axis: Uniaxial crystals exhibit cylindrical symmetry. There is a unique direction in a uniaxial crystal called the optic axis. Values of physical parameters along optic axis are different from the values perpendicular to it. Calcite Quartz
Plane contains optic axis and the direction of propagation Ordinary ray Extraordinary ray Principal Plane: Optic axis Plane contains optic axis and the direction of propagation Calcite
Ordinary ray σ - polarised Polariser/ Analyser Calcite
Extraordinary ray π - polarised Calcite
Polarisation by double refraction Isotropic Medium : Velocity Spherical Uniaxial and Biaxial Crystals Uniaxial : Calcite, Quartz Biaxial: Mica Anisotropic Medium : Velocity ellipsoid
- Polarisation - Polarisation Plane of polarisation is same as This definition is considered in absence of Principal Plane Plane of polarisation is same as plane of incidence (principal plane) - Polarisation Plane of polarisation is perpendicular to the plane of incidence (principal plane) Plane of incidence : plane contains incident ray, reflected/refracted ray, surface normal Plane of polarisation : plane contains electric field vector and direction of propagation Principal plane : Plane contains optic axis and the direction of propagation
Plane of polarisation is same as principal plane e-ray : Plane of polarisation is same as principal plane e-ray in general does not obey the laws of refraction except in case of special cut of crystal (optic axis) o-ray : Plane of polarisation is perpendicular to the principal plane o-ray always obeys the laws of refraction Always e-ray carries -polarisation and o-ray carries -polarisation
Calcite - Negative (ne - no)<0 no = 1.6584 ne = 1.4864 Linear polarisation by double refraction Positive and Negative uniaxial crystals Quartz - Positive (ne - no)>0 no = 1.5443 ne = 1.5534 ne > no ve < vo For sodium D lines Calcite - Negative (ne - no)<0 ne < no ve > vo no = 1.6584 ne = 1.4864 Velocity or Refractive index is the same along the OPTIC AXIS for o-ray and e-ray.
Velocity ellipsoid Quartz Positive crystal ne > no ve < vo Wave surface is the locus of all points reached by the ray at a given instant Velocity ellipsoid Positive crystal Quartz ne > no ve < vo Sphere Spheroid
Positive crystal Quartz ne > no ve < vo Sphere Spheroid
Positive crystal Quartz ne > no ve < vo Sphere Spheroid
Calcite Negative crystal ne < no ve > vo Spheroid Sphere
Calcite Negative crystal ne < no ve > vo Spheroid Sphere
Calcite Negative crystal ne < no ve > vo Spheroid Sphere
Biaxial
Huygens’ construction
Calcite ne < no ve > vo
Special cuts of uniaxial crystal Optic axis normal to the surface of incidence No double refraction
Optic axis parallel to the surface of incidence No double refraction
Oblique Incidence Optic axis parallel to the surface of incidence, normal to the plane of incidence
Nicol prism Calcite no = 1.6584 ne = 1.4864 Canada balsam n = 1.55
Rochon prism
Wollaston prism
Plane polarised Circularly polarised Elliptical and circular polarisation Plane polarised Etc. Circularly polarised
Production of elliptically polarised light
Retarders Quarter wave, Half wave and Full wave
GLASS
Quartz
Half wave plate Quartz
Babinet Compensator is a Variable retarder C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Interference of polarised light Fresnel-Arago laws Two coherent rays polarised at right angles do not interfere 2. Two parallel coherent polarised rays will interfere in the same way as will ordinary light
Optically active medium Rotation of the plane of vibration & Rotatary dispersion Dextrorotatary or right handed medium Levorotatary or left handed medium Specific rotation = 21.72 Deg/mm for Sodium lines
Sugar, Glucose and Fructose Specific rotation Sugar (Sucrose or Cane sugar) o 66.47 Glucose-D ( Dextrose or Grape sugar) o 52.7 Fructose (Levulose or Fruit sugar) o - 92
Rotation in liquids Specific rotation is defined as the observed rotation of light of wavelength 589 nm (the d line of a sodium lamp) passing through 10 cm of a 1 g ml-1 solution of a sample. One can find out the density of substance in solution Specific rotation, [ρ] = 10 θ / ld θ = angle of rotation l = Length of the liquid column in cm d = density in gm/cm3
Fresnel’s explanation of rotation
Induced Optical Effects Isotropic medium can be made optically anisotropic applying Stress : Photoelastic Effect Magnetic field : Faraday Effect Electric field : Kerr effect
Faraday effect d B 0.00001-0.01 min /Gauss-cm =Verdet cosntant
Kerr effect An isotropic medium becomes birefringent by an application of electric field. It behaves like an uniaxial crystal with optic axis in the direction of applied field. K = Kerr Constant