ENGINEERING PHYSICS By G SUNITA DEPARTMENT OF PHYSICS
ENGINEERING PHYSICS By G. SUNITA DEPARTMENT OF PHYSICS K L University
Polarisation Lecture 4
Polarization… Significance of optical Axis Nare. N @ KLU 3
Polarization… Velocities of O-ray and eray:
Polarization… Negative Crystal: E-ray wavefront travels faster than O-ray wave front Velocity of E-ray > Velocity of O-ray Crystals Like Calcite and Tourmaline http: //www. microscopyu. com/print/articles/polarized/birefringence-print. html
Polarization… Positive Crystal: O-ray wavefront travels faster than E-ray wave front Velocity of O-ray > Velocity of E-ray Crystals Like Ice and Quartz http: //www. microscopyu. com/print/articles/polarized/birefringence-print. html
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. http: //www. learnerstv. com/animation. php? ani=90&cat=physics http: //www. edumedia-share. com/media. php? id=970
Polarization… Quarter Wave Plate: It produces the phase difference “п/2” or path difference “λ/4” http: //www. learnerstv. com/animation. php? ani=90&cat=physics http: //www. edumedia-share. com/media. php? id=970
Polarization… Half Wave Plate: It produces the phase difference “п” or path difference “λ/2” Ø HWP produces a phase difference п between Oray and e-ray. Ø Emergent beam from a HWP is plane polarized light. http: //demonstrations. wolfram. com/Polarization. Of. An. Optical. Wave. Through. Polarizers. And. Wave. Pla /
Polarization… Circularly and Elliptically Polarized Light:
Polarization… Circularly and Elliptically Polarized Light: 12
Polarization… Effect of Nicol’s Prism on different polarized lights
Polarization… UPL Partially PL No change in Intensity Imax(2) Imin(2) ≠ 0
Polarization… PPL CPL Imax(2) Imin(2) = 0 No change in Intensity
Polarization… EPL Imax(2) Imin(2) ≠ 0
Polarization… Input UN POLARISED LIGHT Nicol Prism output No change in Intensity 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 Rotated by 360 o Intensity Max (2) Intensity Min(2) not equal to zero PARTIALLY POLARISED LIGHT ELLIPTICALLY POLARISED LIGHT 17
Polarization… Effect of Quarter Wave Plate on Different Polarized Lights 18
Polarization… UPL CPL PPL 19
Polarization… EPL Partially PL 20
Polarization… PPL 0 O, 180 O 45 O, 135 O , 225 O, 315 O EPL At any Angle’s CPL Except the above
Polarization… Input Quarter wave plate output UN POLARISED LIGHT Quarter wave plate UN POLARISED LIGHT CIRCULLARLY POLARISED LIGHT Quarter wave plate PLANE POLARISED LIGHT ELLIPTICALLY POLARISED LIGHT Quarter wave plate PLANE POLARISED LIGHT PARTIALLY 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) PLANE POLARISED LIGHT
Polarization…
Polarization…
Polarization… Problems: 1. Plane polarized light is incident on a piece of quarter cut parallel to the axis. Find the least thickness for which the ordinary and eordinary combine to form plane polarized light. Given
Polarization… 26
Polarization…
Polarization… Production of Polarized Light by different methods: 28
Polarization… 29
Polarization… Polarization by Reflection P . . . X . . . N I= p O r . . . . r= N 1 p R . . . Q Y . . http: //www. launc. tased. edu. au/online/sciences/physics/Polari. htm 30
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… vertical direction of polarization of reflected light • a) horizontally • b) vertically horizontal
Polarization… wearing sunglasses will help reducing glare (reflection) from flat surfaces (highway/water) without with sunglasses
Polarization… Transmitted light is partially polarized Pile of plates Polarizing angle for glass: 57. 5 Inclined at 32. 5
Polarization… Polarization by Transmission: Purely plane polarized
Polarization… DOUBLE REFRACTION
Polarization… Geometry of Calcite Crystal : • • • Known as Iceland spar. It is colourless crystal. It is transparent to ultraviolet and visible light. It belongs to rhombohedral class of hexagonal system. Calcium carbonate (Ca. CO 3). The six faces are parallelograms each having angles 101 o 55’ and 78 o 5.
Polarization… Calcite Crystal : üBlunt Corner üOptic axis üPrinciple section üUniaxial crystals üBiaxial crystals Ca. CO 3 Nare. N @ KLU 38
Polarization… Optic axis : • 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. 39
Polarization… Principle Section: A Plane which contains the optic axis and is perpendicular to two opposite faces is called a principle section. ü Crystal having one optic axis are called uniaxial crystal. Eg: quartz and calcite. ü Crystal having two optics axis are called biaxial crystal. Eg: mica.
Polarization… Double Refraction : (Birefringence) Anisotropic substance : physical prop. are different Experiment 41
Polarization…
O E http: //www. science. smith. edu/geosciences/min_jb/Optics-3. pdf
Polarization… Double Refraction : (Birefringence) 44
Polarization… Double Refraction : (Birefringence) Refractive indices: In case of calcite: When both rays are travel with same velocity along optic axis. 45
Significance of optical Axis
Polarization… Calcite E ray canada balsam O ray 1. Principle 2. Construction 3. Action 4. Limitations 5. Uses
Polarization… Principle : Optical Device. Double Refraction Transmit extra-ordinary ray and cut off Construction: ordinary ray • 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 = 1. 658 µcanada balsam = 1. 55 µe = 1. 486
Polarization… Action: Light entered the faces Canada balsam acts as Rarer medium for O-ray Denser medium for E-ray O-ray: Total internal reflection > critical angle E-ray: Straight line Plane polarized
Polarization… Limitations: 1. Much smaller than the ∠ SMB with face AB – O-ray strikes less than Өc 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=1. 461 3. The velocity of light in water is 2. 2*108 m/s. What is the polarizing angle of incidence foe water surface? (c=3. 8*108 m/s)
http: //demonstrations. wolfram. com/Polarization. Of. An. Optical. Wave. Through. Polarizers. And Wave. Plates/
Polarization… • • Types of polarized lights Detection and production of PPL Production of CPL &EPL Nicol’s prism
- Slides: 57