Part IV Physical Optics Part IV 1 Interference

Part IV. Physical Optics Part IV. 1 • Interference Part IV. 2 • Diffraction Part IV. 3 • Polarization, Scattering, Absorption NSCI 122 Part IV. 1 1

Part IV. 1 • • • Interference Double Slit Diffraction Grating Thin Films Interferometers Holograms NSCI 122 Part IV. 1 2

Interference Amplitude Brightness determined by the intensity of the light wave. Intensity depends on the square of the amplitude. NSCI 122 Part IV. 1 3

Interference Principle of Superposition When waves overlap at a point, add the waves together to find the resulting “superposed” wave. completely in phase constructive interference crest + crest trough + trough big amplitude for superposed wave NSCI 122 Part IV. 1 4

Interference Principle of Superposition When waves overlap at a point, add the waves together to find the resulting “superposed” wave. completely out of phase destructive interference crest + trough small amplitude for superposed wave or no amplitude for superposed wave if waves have equal amplitude NSCI 122 Part IV. 1 5

Interference Constructive Interference 1 2 wavelength 1 2 path difference = m where m = 0, 1, 2… NSCI 122 Part IV. 1 6

Interference Destructive Interference /2 2 1 3 /2 2 1 path difference = (m + ½) where m = 0, 1, 2… NSCI 122 Part IV. 1 7

Interference - Double Slit NSCI 122 Part IV. 1 8

Interference - Double Slit centers of dark fringes centers of bright fringes bright fringe centers and dark fringe centers are equally spaced, a. k. a. “equal-width fringes” NSCI 122 Part IV. 1 9

Interference - Double Slit spacing between fringe centers decreases spacing between fringe centers increases NSCI 122 Part IV. 1 10

Demonstration Video: Double Slit Interference Pattern Watch the demonstration in the lecture video. NSCI 122 Part IV. 1 11

Interference - Double Slit both bright & dark fringe centers have same separation distance NSCI 122 Part IV. 1 12

Interference - Double Slit path difference = 0 1 2 path diff. = 1 path diff. = m path diff. = (m + 1 ) 2 where m is an integer NSCI 122 Part IV. 1 13

Demonstration: Double Slit Interference Using Ripple Tank Applet Watch the applet being used in the lecture video. Demonstration Video: Double Slit Interference using Overhead Projector Watch the demonstration in the lecture video. NSCI 122 Part IV. 1 14

Interference - Diffraction Grating 2 slits 5 slits https: //en. wikipedia. org/wiki/Diffraction_formalism Demonstration Videos: Multiple Slits and Grating Watch the demonstration in the lecture video. NSCI 122 Part IV. 1 15

Interference - Diffraction Grating m = +1 Where are the bright spots? Grating Equation d sin = m m=0 Grating Constant = 1 / d m = -1 path difference = d sin NSCI 122 Part IV. 1 16

Demonstration Videos: Emission Spectra of Excited Gases Watch the demonstrations in the lecture video. NSCI 122 Part IV. 1 17

Interference - Thin Films Light reflects from two surfaces 1 2 ® two beams meet and interfere film Examples: • colors of soap bubble • colors in oil patches on parking lots • antireflection coatings on lenses • ‘Newton’s Rings’ NSCI 122 Part IV. 1 18

Interference - Thin Films https: //en. wikipedia. org/wiki/Thin-film_interference NSCI 122 Part IV. 1 19

Interference - Thin Films Example: Newton’s Rings https: //en. wikipedia. org/wiki/Newton%27 s_rings NSCI 122 Part IV. 1 20

Interference - Interferometers Michelson Interferometer https: //en. wikipedia. org/wiki/Michelson_ interferometer Demonstration Video: Michelson Interferometer Watch the demonstration in the lecture video. NSCI 122 Part IV. 1 21

Interference - Holograms Demonstration Video: Transmission Holograms Watch the demonstration in the lecture video. NSCI 122 Part IV. 1 22