k1-nature of light
TRANSCRIPT
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OPTIKA
Dr. Ahmad Marzuki
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Referensi: Introduction to Optics, F. & L. Pedrotti.
Topik yang dikover: Geometrical optics: < dimension of aperture/object
Wave (i.e. physical) optics:> dimension of aperture/object
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Mengenal Cahaya
Optics
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Mengenal Cahaya
Particle
Isaac Newton (1642-1727)
Optics
Wave
Huygens (1629-1695)
Treatise on Light (1678)
Wave-Particle Duality
De Broglie (1924)
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Young, Fraunhofer and Fresnel
(1800s)
Light as waves!
Interference Thomas Youngs (1773-1829) double slit experiment
see http://members.tripod.com/~vsg/interf.htm
Diffraction Fraunhofer (far-field diffraction)
Augustin Fresnel (1788-1827) (near-field diffraction &polarization)
Electromagnetic waves Maxwell (1831-1879)
http://members.tripod.com/~vsg/interf.htmhttp://members.tripod.com/~vsg/interf.htm -
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Max Plancks Blackbody Radiation
(1900)
Light as particles
Blackbodyabsorbs all wavelengths and
conversely emits all wavelengths
The observed spectral distribution of
radiation from a perfect blackbody did not
fit classical theory (Rayleigh-Jeans law)
ultraviolet catastrophe
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0 20
2x10
7
4x107
6x107
8x107
1x108
T = 5000 K
T = 6000 K
T = 3000 KSpectralRadian
ceExitance
(W/m2 -
mm)
Wavelength (m)
M = T
Cosmic black body background
radiation, T = 3K.
Rayleigh-Jeans law
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Plancks hypothesis (1900)
To explain this spectra, Planck assumedlight emitted/absorbed in discrete units ofenergy (quanta),
E = n hf
Thus the light emitted by the blackbody is,
1
12)(5
2
kThc
e
hcM
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Photoelectric Effect (1905)
Light as particles
Einsteins (1879-1955) explanation light as particles = photons
Kinetic energy = h-
Electrons
Light of frequency
Material with work function
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Luis de Broglies hypothesis (1924)
Wave and particle picture
Postulated that all particles have associated
with them a wavelength,
p
h
For any particle with rest mass mo, treatedrelativistically,
42222 cmcpE o
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Photons and de Broglie
For photons mo= 0
E = pc
Since also E = hf
f
c
chf
h
cE
h
p
h
But the relation c = is just what we expect for
a harmonic wave
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Wave-particle duality
All phenomena can be explained using
either the wave or particle picture
Usually, one or the other is most
convenient
In OPTICS we will use the wave picturepredominantly
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Propagation of light: Huygens
Principle (Hecht 4.4.2)
E.g. a point source (stone dropped inwater)
Light is emitted in all directionsseries of
crestsand troughs
Rayslines
perpendicular to
wave fronts
Wave front- Surface of
constant phase
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Terminology
Spherical waveswave fronts are
spherical
Plane waveswave fronts are planes
Rayslines perpendicular to wave fronts
in the direction of propagation
x
Planes parallel to y-z plane
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Huygens principle
Every point on a wave front is a source of
secondary wavelets.
i.e. particles in a medium excited by
electric field (E) re-radiatein all directions
i.e. in vacuum, E, B fields associated with
wave act as sourcesof additional fields
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Huygens wave front construction
Given wave-front at t
Allow wavelets to evolve
for timet
r = ct
New wavefront
What aboutrdirection?
See Bruno Rossi Optics. Reading, Mass:Addison-Wesley Publishing Company, 1957, Ch. 1,2
for mathematical explanation
Construct the
wave front tangentto the wavelets
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Plane wave propagation
New wave front is stilla plane as long asdimensions of wavefront are >>
If not, edge effectsbecome important
Note: no such thing
as a perfect planewave, or collimatedbeam