K L University By G.SUNITA DEPARTMENT OF PHYSICS

Polarisation Lecture 4

KLU Significance of optical Axis Polarization…

Velocities of O-ray and e-ray: Polarization…

Negative Crystal: Polarization… E-ray wavefront travels faster than O-ray wave front Velocity of E-ray > Velocity of O-ray Crystals Like Calcite and Tourmaline

Positive Crystal: Polarization… O-ray wavefront travels faster than E-ray wave front Velocity of O-ray > Velocity of E-ray Crystals Like Ice and Quartz

Polarization… Wave Plate: A waveplate or retarder is an optical device that alters the polarization state of a light wave travelling through it. Wave plate Quarter wave plate Half wave plate

Polarization… Quarter Wave Plate: It produces the phase difference “п/2” or path difference “λ/4” Calcite crystal cut with optic axis parallel to the surface.

Polarization… Quarter Wave Plate: It produces the phase difference “п/2” or path difference “λ/4”

Polarization… It produces the phase difference “п” or path difference “λ/2”  HWP produces a phase difference п between O-ray and e-ray.  Emergent beam from a HWP is plane polarized light. Half Wave Plate:

Circularly and Elliptically Polarized Light: Polarization…

12 Polarization… Circularly and Elliptically Polarized Light:

Polarization… Effect of Nicol’s Prism on different polarized lights

Polarization… No change in Intensity UPL Partially PL I max (2) I min (2) ≠ 0

Polarization… PPL I max (2) I min (2) = 0 CPL No change in Intensity

Polarization… EPL I max (2) I min (2) ≠ 0

17 Polarization… InputNicol Prismoutput UN POLARISED LIGHT Rotated by 360 o No change in Intensity PARTIALLY POLARISED LIGHT Rotated by 360 o Intensity Max (2) Intensity Min(2) not equal to zero PLANE POLARISED LIGHT Rotated by 360 o Intensity Max (2) Intensity Min(2) equal to zero CIRCULLARLY POLARISED LIGHT Rotated by 360 o No change in Intensity ELLIPTICALLY POLARISED LIGHT Rotated by 360 o Intensity Max (2) Intensity Min(2) not equal to zero

18 Polarization… Effect of Quarter Wave Plate on Different Polarized Lights

19 Polarization… UPL CPLPPL

20 Polarization… EPLPPL Partially PL

Polarization… PPL 0 O, 180 O CPL 45 O, 135 O, 225 O, 315 O EPL At any Angle’s Except the above

Polarization… InputQuarter wave plateoutput UN POLARISED LIGHTQuarter wave plateUN POLARISED LIGHT CIRCULLARLY POLARISED LIGHT Quarter wave platePLANE POLARISED LIGHT ELLIPTICALLY POLARISED LIGHT Quarter wave platePLANE POLARISED LIGHT PARTIALLY POLARISED LIGHT Quarter wave plate PARTIALLY POLARISED LIGHT PLANE POLARISED LIGHT Quarter wave plate (rotated from 0 o to 360 o ) PPL (0 o, 180 o ) CPL (45 o, 135 o, 225 o, 315 o ) EPL (Any angle)

Polarization…

26 Polarization…

28 Polarization… Production of Polarized Light by different methods:

29 Polarization…

30 Polarization… XY N N1 P O Q R Polarization by Reflection I = p r = p r. N1 R...

Polarization… Polarization by Reflection Brewster’s law- That the tangent angle of polarization (p) is numerically equal to the refractive index(µ) of the medium.

Polarization… a) horizontally b) vertically horizontal vertical direction of polarization of reflected light

Polarization… wearing sunglasses will help reducing glare (reflection) from flat surfaces (highway/water) withoutwith sunglasses

Polarization… Pile of plates Polarizing angle for glass: 57.5 Inclined at 32.5 Transmitted light is partially polarized

Polarization… Purely plane polarized

Polarization…

Geometry of Calcite Crystal : K nown as Iceland spar. I t is colourless crystal. I t is transparent to ultraviolet and visible light. I t belongs to rhombohedral class of hexagonal system. C alcium carbonate (CaCO3). T he six faces are parallelograms each having angles 101 o 55 ’ a nd 78 o 5.

38 Calcite Crystal : CaCO3 Blunt Corner Optic axis Principle section Uniaxial crystals Biaxial crystals KLU

Optic axis : 39 An imaginary line passing through one of the blunt corners and making equal angles with all the three faces is called optic axis. Optic axis is not an imaginary line but it is a direction. Any line parallel to optic axis also acts as optic axis. Polarization…

41 Double Refraction : (Birefringence) Experiment Polarization… Anisotropic substance : physical prop. are different

Polarization…

O E

44 Double Refraction : (Birefringence) Polarization…

45 Double Refraction : (Birefringence) Polarization… Refractive indices: In case of calcite: When both rays are travel with same velocity along optic axis.

Significance of optical Axis

Polarization… 1.Principle 2.Construction 3.Action 4.Limitations 5.Uses Calcite canada balsam O ray E ray

Principle : Optical Device. Double Refraction Transmit extra-ordinary ray and cut off ordinary ray Construction: Length is 3 times as its width End Faces grounded – 68 and 112 instead of 71 and 109 Cut into two pieces – grounded – polished – cemented (With Canada balsam). Polarization…

µₒ = µ e = µ canada balsam = 1.55

Polarization… Action: Light entered the faces Canada balsam acts as Rarer medium for O-ray Denser medium for E-ray E-ray: Straight line Plane polarized O-ray: Total internal reflection > critical angle

Polarization… Limitations: 1.Much smaller than the ∠ SMB with face AB – O-ray strikes less than Ө c Both O-ray and E-rays transmitted Angle of incidence : 14 ◦ 2.Angle grater than ∠ SMB with face AB -- E-ray will refract suffer total reflection --- No light To obtain plane polarized light, the incident beam should be confined with an angle of 14 on either side of SM

Polarization… Uses: Polarizer Analyzer

Polarization… 1. A Ray of light is incident on the surface of glass plate µ=1.56 at the polarizing angle. Calculate the angle of refraction. 2. Calculate the Brewster angle for the following liquids Ethyl alcohol, µ=1.361 Carbon tetrachloride µ= The velocity of light in water is 2.2*10 8 m/s. What is the polarizing angle of incidence foe water surface? (c=3.8*10 8 m/s)

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Polarization… Types of polarized lights Detection and production of PPL Production of CPL &EPL Nicol’s prism