Download presentation

Presentation is loading. Please wait.

Published byJorge Rosborough Modified over 2 years ago

1
Agenda Monday –Diffraction – Problems –How small? –How many? Tuesday –Diffraction – Laboratory, Quiz on Interference Wed –Review Fri –Bonus Quiz

2
Basic Diffraction Formula x = m (constructive) x = (m+1/2) (constructive) –m integer Open question –What is x?

3
Multiple Slits x = m (constructive) x = (m+1/2) (constructive) –m integer Open question – x = dsin

4
Equation vs. Experiment Coherent, monochromatic Light wavelength Slits (Turned perp.) Rectangular Screen m 3 2 1 0 -2 -3 dsin( ) = m d

5
Examine Situation for Given Laser Means: fixed Coherent, monochromatic Light wavelength Slits (Turned perp.) Screen m 3 2 1 0 -2 -3 dsin( ) = m d

6
Range of possible d values? Given: fixed Coherent, monochromatic Light wavelength Slits (Turned perp.) Screen m 3 2 1 0 -2 -3 dsin( ) = m d

7
Range of possible d values? Given: fixed dsin( ) = m d = m / sin( ) Anything related to range of d? Try big & small….

8
Range of possible d values? Given: fixed dsin( ) = m d = m / sin( ) How big can d be? Pretty big, m can range to infinity…. If d is big, what happens to angle? sin( ) = m /d…. Large slit spacing, all diffraction squeezed together Interference exists – just all overlaps – beam behavior

9
Large Distance (Assume large width…) Coherent, monochromatic Light wavelength Slits (Turned perp.) Screen d dsin( ) = m Slit one Slit Two

10
Range of possible d values? Given: fixed dsin( ) = m d = m / sin( ) How small can d be? Pretty small, m can be zero How about for anything but m = 0 Smallest m =1 d = /sin( ) d small when sin( ) big, sin( ) <= 1 smallest d for m=1 diffraction: d = Replace: sin( )=m sin( ) = m implies if d =, three diffraction spots if d <, no diffraction (m=0?)

11
Range of possible d values? Given: fixed Coherent, monochromatic Light wavelength Slits (Turned perp.) Screen m 1 0 dsin( ) = m d ~

12
What Happens? Diffraction from spacing & width –Overlaying patterns, superposition 3 slits, all same spacing –Very similar to two slits Tons of slits, all same spacing –Refined interference. Focused maxima Move screen farther away from slits –Bigger angle/distance on screen Move light source, leave rest same –Nothing

13
Resolution When can you identify 2 objects? Coherent, monochromatic Light wavelength Slits (Turned perp.) Screen m 1 0 dsin( ) = m d ~ w ~ Not Here…

14
Resolution When can you identify 2 objects? Begin with diffraction Diffraction of light through a circular aperture 1 st ring (spot) sin( ) = 1.22 /D Same setup idea as before

15
Resolution When can you identify 2 objects? Begin with diffraction Diffraction of light around a circular block 1 st ring (spot) sin( ) = 1.22 /D Same setup idea as before Things that might cause diffraction rings… Pits/dust on glasses Iris of your eye Telescope Lens Raindrops

16
Pretty Picture Moon Raindrop What you see

17
Headlights Resolved (barely) Unresolved

18
Issue How close must a car be before you can tell it is NOT a motorcycle. (assume both headlights work) sin( ) = 1.22 /D 1.5 m Small Angle sin( ) ~ tan( ) ~ [radians]

19
Issue How close must a car be before you can tell it is NOT a motorcycle. (assume both headlights work) = 1.22 /D = y/L What is D? 1.5 m = y Small Angle sin( ) ~ tan( ) ~ [radians] L

20
Issue How close must a car be before you can tell it is NOT a motorcycle. (assume both headlights work) = 1.22 /D = y/L pupil: D ~ 5 mm What is ? 1.5 m = y Small Angle sin( ) ~ tan( ) ~ [radians] L

21
Issue How close must a car be before you can tell it is NOT a motorcycle. (assume both headlights work) = 1.22 /D = y/L pupil: D ~ 5 mm GREEN ~ 500 nm Calculation Time 1.5 m = y Small Angle sin( ) ~ tan( ) ~ [radians] L

22
Issue How close must a car be before you can tell it is NOT a motorcycle. (assume both headlights work) = 1.22 /D = y/L y/L = 1.22 /D L/y = D/(1.22 ) 1.5 m = y Small Angle sin( ) ~ tan( ) ~ [radians] L = 500 nm D = 5 mm

23
Issue How close must a car be before you can tell it is NOT a motorcycle. (assume both headlights work) = 1.22 /D L/y = D/(1.22 ) L = Dy/(1.22 ) = 12km ~ 7 miles Little far, but not crazy far aberrations blur image more here 1.5 m = y Small Angle sin( ) ~ tan( ) ~ [radians] L = 500 nm D = 5 mm

24
Agenda Monday –Diffraction – Problems Tuesday –Diffraction – Laboratory, Quiz on Interference Wed –Review Fri –Bonus Quiz

Similar presentations

OK

PHY 1371Dr. Jie Zou1 Chapter 38 Diffraction and Polarization (Cont.)

PHY 1371Dr. Jie Zou1 Chapter 38 Diffraction and Polarization (Cont.)

© 2017 SlidePlayer.com Inc.

All rights reserved.

Ads by Google