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Chapter 5: Wave Optics How to explain the effects due to interference, diffraction, and polarization of light? How do lasers work? Wave Optics Effects due to interference, diffraction, and polarization can not be explained by geometric optics.
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How to explain the effects due to interference, diffraction, and polarization of light?
How do lasers work?
In phase waves
lead to constructive
Out of phase waves
lead to destructive
Path difference P = (r2 – r1)
Path difference = 1 wavelength
Path difference = 1/2 wavelength
Condition for constructive interference:
n = 0, 1, 2, …
The phase difference of rays reflected from the top and bottom surfaces depends on the thickness and refractive index of the film, the angle at which the light strikes the film surface and the wavelength of the light.
The substrate (glass, quartz, etc.) is coated with a thin layer of material so that reflections from the outer surface of the film and the outer surface of the substrate cancel each other by destructive interference.
Diffraction pattern from a
Diffraction of light from a CD
A diffraction phenomenon
A grating has 5000 lines/cm. A second order maximum is observed at 300. What is the wavelength of light?
Absorption: Atom can absorb a photon and become excited.
Spontaneous emission: Atom in excited state will spontaneously emit a
photon and occupy a lower energy state.
Stimulated emission: Atom in excited state is stimulated by a photon
to emit another photon and occupy a lower energy state. Emitted photon has the same wavelength, phase, and direction as the stimulating photon.
achieved by “pumping”
1. Pumping: Excites atoms to highest level.
2. Fast radiative decay to reservoir creates
population inversion between reservoir and
3. Seed photon stimulates emission and
light is amplified!
Interference pattern is recorded on film.
Need high resolution (slow) film, long
exposure and vibration free set up.
Interference pattern acts
as a diffraction grating
so different orders of
maxima and minima
reconstruct the image.