Lect24 - Physics 212 Le cture24 Pol 30 20 10 0 Confused Avg...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Physics 212 Le cture24: Polarization 50 40 30 20 10 0 Confused Avg = 2.8 Confident Physics 212 Le cture24, S 1 lide Music Who is the Artist? A) B) C) D) E) Leadbelly Robert Johnson Son House Mississippi John Hurt Elmore James BB I do re e be mm r his“re discove in the ry” 60’s. 60’s. C lassic de blue lta s The eof thewe k: Maste of theBlue m e rs s The All Blue arenot thesam s e BB King & Mississippi John Hurt Physics 212 Le cture24, S 2 lide Physics 212 Le cture24: Polarization 50 40 30 20 10 0 Confused Avg = 2.8 Confident Physics 212 Le cture24, S 3 lide S far wehaveconside d planewave that look likethis: o re s Fromnow on just draw E and re e be that B is still the : mm r re Physics 212 Le cture24, S 4 lide Line Polarization ar Physics 212 Le cture24, S 5 lide Theinte The nsity of a wave doe not de nd on its s pe doe polarization: I = ε 0c E 2 2 = ε 0 c Ex2 + E y 2 = ε 0 c Ex2 + E y = ε 0 cE02 sin 2 (kz − ωt − φ ) (sin 2 θ + cos 2 θ ) 12 S I= o 1 Just likebe fore Physics 212 Le cture24, S 6 lide 1 ε 0cE02 2 Polarize rs Them cular structureof a polarize cause thecom nt of r s pone The ole t heE f ie pe ndicular to theTransm ld rpe ission Axis to beabsorbe d. Anim ation Physics 212 Le cture24, S 7 lide Physics 212 Le cture24, S 8 lide Pre flight 2 Two Polarize rs BB 70 60 50 40 30 20 10 0 These cond polarize is orthogonal to thefirst r no light will com through. e cos(90o) = 0 Physics 212 Le cture24, S 9 lide Pre flight 3 Two Polarize rs BB 80 60 40 20 0 Any non-horizontal polarize afte thefirst polarize will produce r r r polarize light AT THAT ANGLE d Part of that light will m it through thehorizontal polarize ake r Physics 212 Le cture24, S 10 lide 10 The is no re re ason that φ has to bethesam for Ex and Ey: e Making φ x diffe nt from φ y cause circular or e re s lliptical polarization: Making diffe cause Example: π φx − φ y = 90o = 2 θ = 45o = π 4 At t=0 Ex = Ey = E0 2 E0 2 cos(kz − ωt ) sin(kz − ωt ) RC P Physics 212 Le cture24, S 11 lide 11 Q: How do wechange t here lativephase be e Ex and Ey? twe n A: Bire fringe nce By picking theright thickne wecan change ss t hickne there lativephaseby e xactly 90o. This change line t o s line ar circular polarization circular and is calle a d quarte waveplate r quarte Physics 212 Le cture24, S 12 lide 12 Right hand Right rule rule This m s This odification doe not not changetheinte nsity change e r: ithe I = ε 0c E 2 2 = ε 0 c Ex2 + E y Right Handed Circular Polarization (at t = 0) E02 = ε 0c sin 2 (kz − ωt ) + cos 2 (kz − ωt ) 2 1 1 2 S I = ε 0 cE0 o 2 Just likebe fore Physics 212 Le cture24, S 13 lide 13 Right or Le ??? ft Right circularly polarize d Do right hand rule Finge along slow dire rs ction C into fast dire ross ction I f thum points in dire b ction of propagation: RC P Physics 212 Le cture24, S 14 lide 14 C ircular Light on Line Polarize ar r Q: What happe whe circularly ns n polarize light is put through a d polarize along they (or x) axis ? r polarize BB A) I = 0 B) I = ½ I 0 C) I = I I = ε 0c E 2 0 = ε 0 c Ex2 + Xy E2 E02 = ε 0c cos 2 (kz − ωt ) 2 11 = ⋅ ε 0 cE02 22 Half of be fore 12 Physics 212 Le cture24, S 15 lide 15 A B Pre flight 6 BB 50 C A: ase Ex is absorbe d C B: ase (Ex,Ey) phasechange d 40 30 20 I A = I 0 cos 2 (45o ) I A = 1 I0 2 I B = I0 10 0 Physics 212 Le cture24, S 16 lide 16 I nte nsity: 2 I = ε 0 c Ex2 + E y E AS PH QW Plate CH AN GE Both Ex and Ey arestill the , so re inte nsity is thesam e Physics 212 Le cture24, S 17 lide 17 2 I = ε 0 c Ex2 + E y B OR S AB Polarize r CO MP ON EN T Ex is m issing, so inte nsity is lowe r Physics 212 Le cture24, S 18 lide 18 A B Pre flight 8 BB 40 30 RC P 1/4 λ Z 20 10 0 Physics 212 Le cture24, S 19 lide 19 A B Pre flight 10 BB 50 40 30 ½λ Z Z 20 10 0 Physics 212 Le cture24, S 20 lide 20 Exe cutiveS m um ary: Polarize & QW Plate rs s: Polarized Light Circularly or Un-polarized Light Bire fringe nce RCP Ex = E0 cos(kx) 2 Ey = E0 sin( kx ) 2 Physics 212 Le cture24, S 21 lide 21 De os: m What e can weput in the to changethepolarization? lse re Physics 212 Le cture24, S 22 lide 22 C alculation Light is incide on two line polarize and a quarte waveplate(QWP) as shown. nt ar rs r What is the intensity I3 in terms of I1? y x 45o fast slow 60o I1 I2 I3 z • Conceptual Analysis ar rs: ld pone rpe • Line Polarize absorbs E fie com nt pe ndicular to TA r s: hifts phaseof E fie com nts in fast-slow dire ld pone ctions • Quarte WavePlate S • Strategic Analysis te ine nsity re duction afte e obje r ach ct • De rm stateof polarization and inte nsity re ductions to ge final re t duction. • Multiply individual inte Physics 212 Le cture24, S 23 lide 23 C alculation Light is incide on two line polarize and a quarte waveplate(QWP) as shown. nt ar rs r y x 45o fast E1 slow RC P Ex Ey 60o I1 λ /4 I2 BB BB I3 z • What is the polarization of the light after the QWP? y y x (A) LCP (B) RCP (C) (D) x (E) unpolarized Light incident on QWP is linearly polarized at 45o t o fast axis LC or RCP? Easie way: Right P st Hand Rule : Light will be circularly polarized after QWP C finge of RH back to front url rs Thum points in dir of propagation b if right hand polarize d. RC P Physics 212 Le cture24, S 24 lide 24 C alculation Light is incide on two line polarize and a quarte waveplate(QWP) as shown. nt ar rs r y x 45o fast E1 slow RC P Ex Ey 60o I1 λ /4 I2 BB I3 z • What is the intensity I2 of the light after the QWP? (A) I2 = I 1 BEFORE: Ex = Ey = E1 sin(kz − ωt ) 2 E1 sin(kz − ωt ) 2 (B) I 2 = ½ I 1 (C) I 2 = ¼ I 1 AFTER: Ex = Ey = E1 cos(kz − ωt ) 2 E1 sin(kz − ωt ) 2 No absorption: Just a phasechange! I = ε 0c E 2 x +E 2 y S ebe & afte ! am fore r Physics 212 Le cture24, S 25 lide 25 C alculation Light is incide on two line polarize and a quarte waveplate(QWP) as shown. nt ar rs r y x 45o fast E1 slow RC P Ex Ey 60o I1 E3 λ /4 I2= I1 BB I3 z • What is the polarization of the light after the 60o polarizer? y (A) LCP (B) RCP (C) 60o x (D) 60o y x (E) unpolarized Absorption: only passe com nts of E paralle to TA (θ = 60 ) s pone l Ey 60 E 3 E3 = Ex sin θ + E y cos θ E1 ( cos(kz − ωt ) sin θ + sin(kz − ωt ) cos θ ) 2 E3 = E1 ( sin(kz − ωt + θ ) ) 2 E3 = Ex Physics 212 Le cture24, S 26 lide 26 C alculation Light is incide on two line polarize and a quarte waveplate(QWP) as shown. nt ar rs r y x 45o fast E1 slow RC P Ex Ey 60o I1 E3 λ /4 I2= I1 BB 3 II3 = ½ I 1 z • What is the intensity I3 of the light after the 60o polarizer? (A) I 3 = I 1 E E3 = 1 2 (B) I 3 = ½ I 1 (C I 3 = ¼ I 1 ) I3 = 1 I1 2 I ∝ E2 Ey 60 E 3 NOTE: This doe not de nd on θ !! s pe Ex Physics 212 Le cture24, S 27 lide 27 Follow Up 1 Re placethe60o polarize with anothe QWP as shown. r r y x 45o fast E slow Ex RC P Ey slow E3 Ey Ex z I1 fast λ /4 I2= I1 I3 BB • What is the polarization of the light after the last QWP? y y x (A) LCP (B) RCP (C) (D) x (E) unpolarized Easiest way: Efast is λ /4 ahe of Eslow ad Brings Ex and Ey back in phase!! Physics 212 Le cture24, S 28 lide 28 Follow Up 2 Re placethe60o polarize with anothe QWP as shown. r r y x 45o fast E slow Ex RC P Ey slow E3 Ey Ex z I1 fast λ /4 I2= I1 I3= I1 BB • What is the intensity I3 of the light after the last QWP? (A) I1 BEFORE: Ex = E1 cos(kz − ωt ) 2 I before (B) ½ I 1 (C) ¼ I 1 AFTER: Ex = I after E12 = 2 Ey = No absorption: Just a phasechange! I nte nsity = < E2 > E12 = 2 E1 cos(kz − ωt ) 2 E1 cos(kz − ωt ) 2 E E y = 1 sin(kz − ωt ) 2 Physics 212 Le cture24, S 29 lide 29 Follow Up 3 C onside light incide on two line polarize as shown. S r nt ar rs upposeI 2 = 1/8 I 0 y x E1 60o I0 I1 I 1 = ½I 0 E2 I2 = 1/8 I0 z BB • What is the possible polarization of the INPUT light? (A) LCP y (B) 45 o x (C) unpolarized (D) all of above (E) none of above r r: nsity I 1 • Afte first polarize LP along y-axis with inte r cond polarize LP at 60o wrt y-axis r: • Afte se nsity: I 2 = I 1cos2(60o) = ¼ I 1 • I nte • I 2 = 1/8 I 0 I 1 = ½ I 0 Que stion is: What kind of light lose ½ of its inte s nsity afte r passing through ve rtical polarize r? Answe Eve r: rything e pt LP at θ othe than 45o xce r Physics 212 Le cture24, S 30 lide 30 ...
View Full Document

This note was uploaded on 03/05/2011 for the course PHYS 212 taught by Professor Kim during the Spring '08 term at University of Illinois, Urbana Champaign.

Ask a homework question - tutors are online