k1-nature of light

8/10/2019 K1-Nature of Light

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OPTIKA

Dr. Ahmad Marzuki

[email protected]


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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

k1-nature of light

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