oxford physics: second year, optics - university of oxford · · 2014-01-22• lecture notes: on...
TRANSCRIPT
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P. Ewart
The science of light
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• Lecture notes: On web site
NB outline notes!
• Textbooks:
Hecht, Optics
Lipson, Lipson and Lipson, Optical Physics
Further reading:
Brooker, Modern Classical Optics
• Problems: Material for four tutorials
plus past Finals papers A2
• Practical Course: Manuscripts and Experience
Oxford Physics: Second Year, Optics
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Structure of the Course
1. Physical Optics (Interference) Diffraction Theory (Scalar)
Fourier Theory
2. Analysis of light (Interferometers)
Diffraction Gratings
Michelson (Fourier Transform)
Fabry-Perot
3. Polarization of light (Vector)
Oxford Physics: Second Year, Optics
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Oxford Physics: Second Year, Optics
Astronomical observatory, Hawaii, 4200m above sea level.
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Oxford Physics: Second Year, Optics
Multi-segment
Objective mirror,
Keck Obsevatory
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Oxford Physics: Second Year, Optics
Hubble Space Telescope, HST,
In orbit
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Oxford Physics: Second Year, Optics
HST Deep Field
Oldest objects
in the Universe:
13 billion years
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Oxford Physics: Second Year, Optics
HST Image: Gravitational lensing
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Oxford Physics: Second Year, Optics
SEM Image:
Insect head
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Oxford Physics: Second Year, Optics
Coherent Light:
Laser physics:
Holography,
Telecommunications
Quantum optics
Quantum computing
Ultra-cold atoms
Laser nuclear ignition
Medical applications
Engineering
Chemistry
Environmental sensing
Metrology ……etc.!
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Oxford Physics: Second Year, Optics
CD/DVD Player: optical tracking assembly
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• Astronomy and Cosmology
• Microscopy
• Spectroscopy and Atomic Theory
• Quantum Theory
• Relativity Theory
• Lasers
Oxford Physics: Second Year, Optics
Optics in Physics
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Oxford Physics: Second Year, Optics
Lecture 1: Waves and Diffraction
• Interference
• Analytical method
• Phasor method
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Oxford Physics: Second Year, Optics
u
t, x
T
Time
or distance
axis
t,z
u
Phase change of 2p
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Oxford Physics: Second Year, Optics
dsin
d
r1
r2
P
D
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Oxford Physics: Second Year, Optics
Real
Imag
inar
y
u
Phasor diagram
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Oxford Physics: Second Year, Optics
u /roup
u /ro
Phasor diagram for 2-slit interference
uo r
uo r
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Oxford Physics: Second Year, Optics
Lecture 2: Diffraction theory
• Diffraction at a finite slit - Analytical method
- Phasor method
• 2-D diffraction at apertures
• Fraunhofer diffraction
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Oxford Physics: Second Year, Optics
ysin
+a/2
-a/2
r
r y+ sin
P
D
y dy
Diffraction from a single slit
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Oxford Physics: Second Year, Optics
-10 -5 0 5 10
0.0
0.2
0.4
0.6
0.8
1.0
pp p ppp
sinc2()
Intensity pattern from
diffraction at single slit
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Oxford Physics: Second Year, Optics
asin
+a/2
-a/2
r
P
D
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Oxford Physics: Second Year, Optics
/
RO
R
R =
P
P
Phasors and resultant
at different angles
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Oxford Physics: Second Year, Optics
R RP
R sin /2
R
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Oxford Physics: Second Year, Optics
Phasor arc tofirst minimum
Phasor arc tosecond minimum
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Oxford Physics: Second Year, Optics
y
x
z
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Diffraction from a rectangular aperture
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Oxford Physics: Second Year, Optics
Intensity
y
x
Diffraction pattern from circular aperture
Point Spread Function
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Diffraction from a circular aperture
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Diffraction from circular apertures
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Oxford Physics: Second Year, Optics
Dust
pattern
Diffraction
pattern
Basis of particle sizing instruments
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Oxford Physics: Second Year, Optics
Lecture 3: Diffraction theory
and wave propagation
• Fraunhofer diffraction
• Fresnel’s theory of wave propagation
• Fresnel-Kirchoff diffraction integral
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Oxford Physics: Second Year, Optics
Fraunhofer Diffraction
How linear is linear?
A diffraction pattern for which the
phase of the light at the
observation point is a
linear function of the position
for all points in the diffracting
aperture is Fraunhofer diffraction
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Oxford Physics: Second Year, Optics
R
R R
R
a a
diffracting aperture
source observingpoint
<
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Oxford Physics: Second Year, Optics
Fraunhofer Diffraction
A diffraction pattern formed in the image
plane of an optical system is
Fraunhofer diffraction
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Oxford Physics: Second Year, Optics
O
P
A
BC
f
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Oxford Physics: Second Year, Optics
u v
Equivalent lenssystem
Fraunhofer diffraction: in image plane of system
Diffracted
waves
imaged
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Oxford Physics: Second Year, Optics
(a)
(b)
O
O
P
P
Equivalent lens system:
Fraunhofer diffraction is independent of aperture position
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Oxford Physics: Second Year, Optics
Fresnel’s Theory of wave propagation
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Oxford Physics: Second Year, Optics
dS
n
r
Pz-z 0
Plane wave surface
Huygens secondary sources on wavefront at -z
radiate to point P on new wavefront at z = 0
unobstructed
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Oxford Physics: Second Year, Optics
rn
q
n
P
Construction of elements of equal area on wavefront
rn
q
n
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Oxford Physics: Second Year, Optics
(q+ /2)
q
p
Rp
First Half Period Zone
(q+/2)
q
p
Rp
Resultant, Rp, represents amplitude from 1st HPZ
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Oxford Physics: Second Year, Optics
p
/2
q
q
PO
Phase difference of /2
at edge of 1st HPZ
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Oxford Physics: Second Year, Optics
As n a infinity resultant a ½ diameter of 1st HPZ
Rp
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Oxford Physics: Second Year, Optics
Fresnel-Kirchoff diffraction integral
ikrop e
r
Suiu )rn,(
d
Fresnel-Kirchoff diffraction integral
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Oxford Physics: Second Year, Optics
Babinet’s Principle
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Oxford Physics: Second Year, Optics
Lectures 1 - 3: The story so far
• Scalar diffraction theory:
Analytical methods
Phasor methods
• Fresnel-Kirchoff diffraction integral:
propagation of plane waves
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Oxford Physics: Second Year, Optics
Gustav Robert Kirchhoff
(1824 –1887)
Joseph Fraunhofer
(1787 - 1826)
Augustin Fresnel
(1788 - 1827)
Fresnel-Kirchoff Diffraction Integral
ikrop e
r
Suiu )rn,(
d
Phase at observation is
linear function of position
in aperture:
= k sin y
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Oxford Physics: Second Year, Optics
Lecture 4: Fourier methods
• Fraunhofer diffraction as a
Fourier transform
• Convolution theorem – solving difficult diffraction problems
• Useful Fourier transforms and convolutions
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Oxford Physics: Second Year, Optics
ikrop ern
r
uiu ).(
dS
xexuAu xi
p d)()(
Fresnel-Kirchoff diffraction integral:
Simplifies to:
where = ksin
Note: A() is the Fourier transform of u(x)
The Fraunhofer diffraction pattern is proportional to the Fourier transform of the transmission function (amplitude function) of the diffracting aperture
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Oxford Physics: Second Year, Optics
'd).'().'()()()( xxxgxfxgxfxh
The Convolution function:
The Convolution Theorem:
The Fourier transform, F.T., of f(x) is F()
F.T., of g(x) is G()
F.T., of h(x) is H()
H() = F().G()
The Fourier transform of a convolution of f and g
is the product of the Fourier transforms of f and g
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Oxford Physics: Second Year, Optics
Monochromatic
Wave
Fourier
Transform
T
.o p/T
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Oxford Physics: Second Year, Optics
xo x
V(x)
V( )
-function
Fourier transform
Power spectrum
V()V()* = V2
= constant
V
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Oxford Physics: Second Year, Optics
xS x
V(x)
V( )
Comb of -functions
Fourier transform
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g(x-x’ ) f(x’ )
h(x)
Constructing a double slit function by convolution
Oxford Physics: Second Year, Optics
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g(x-x’ ) f(x’ )
h(x)
Triangle as a convolution of two “top-hat” functions
This is a self-convolution or Autocorrelation function
Oxford Physics: Second Year, Optics
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Oxford Physics: Second Year, Optics
Lecture 5: Theory of imaging
• Fourier methods in optics
• Abbé theory of imaging
• Resolution of microscopes
• Optical image processing
• Diffraction limited imaging
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Joseph Fourier (1768 –1830)
Oxford Physics: Second Year, Optics
• Heat transfer theory:
- greenhouse effect
• Fourier series
• Fourier synthesis and analysis
• Fourier transform as analysis
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Ernst Abbé (1840 -1905)
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Oxford Physics: Second Year, Optics
a
dd’
f Du v
u(x) v(x)
Fourier plane
Abbé theory of imaging (coherent light)
Fourier plane
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Oxford Physics: Second Year, Optics
The compound microscope
Objective magnification = v/u Eyepiece magnifies real image of object
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Diffracted orders from high spatial frequencies miss the objective lens
So high spatial frequencies are missing from the image.
max defines the numerical aperture… and resolution
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Oxford Physics: Second Year, Optics
Fourier
plane
Image
plane
Image processing
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Oxford Physics: Second Year, Optics
Optical simulation of
“X-Ray diffraction”
a b
a’ b’
(a) and (b) show objects:
double helix
at different angle of view
Diffraction patterns of
(a) and (b) observed in
Fourier plane
Computer performs Inverse Fourier transform To find object “shape”
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Oxford Physics: Second Year, Optics
a
dd’
f Du v
u(x) v(x)
Fourier plane
amplitude or phase object
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Oxford Physics: Second Year, Optics Schlieren photography
Source
CollimatingLens
ImagingLens
KnifeEdge
ImagePlane
Refractiveindex variation
Fourier
Plane
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Schlieren photography of combustion
Schlieren film of ignition
Courtesy of Prof C R Stone
Eng. Science, Oxford University
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Oxford Physics: Second Year, Optics
Intensity
y
x
Diffraction pattern from circular aperture
Point Spread Function, PSF
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Oxford Physics: Second Year, Optics
Lecture 6: Optical instruments and
Fringe localisation
• Interference fringes
• What types of fringe?
• Where are fringes located?
• Interferometers
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Oxford Physics: Second Year, Optics
• Interference by:
• Division of wavefront - Young’s slits: 2 beams
- N-slit grating: multiple beams
• Division of amplitude - Michelson: 2 beams
- Fabry-Perot: multiple beams
What kind of interference fringes and where are they?
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Oxford Physics: Second Year, Optics
What kind of interference fringes and where are they?
Depends on: Type of light source – Point source - Extended source Division of wavefront – Point sources Division of amplitude by – Reflection from: Wedged surfaces Parallel surfaces
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Oxford Physics: Second Year, Optics
non-localised fringes
Plane
waves
Division of wavefront Young’s slits
Usually observed under Fraunhofer conditions – large distance from slits
Non-localized fringes
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Z
Oxford Physics: Second Year, Optics
to 8
f
Plane
waves
Fraunhofer condition
Division of wavefront Diffraction grating
Fringes localized at infinity
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Oxford Physics: Second Year, Optics
P’
P
O
Wedged reflecting surfaces Point source
Division of Amplitude
Fringes of Equal thickness
Non-localized
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Oxford Physics: Second Year, Optics
OPP’
’
Parallel reflecting surfaces Point source
Division of Amplitude
Fringes of Equal inclination
Non-localized
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Oxford Physics: Second Year, Optics
P’
P
R
OS
R’
Wedged Reflecting surfaces
Extended source
Division of Amplitude
Localized in plane of wedge, near apex
Equal thickness
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Oxford Physics: Second Year, Optics
t
2t=x
sourceimages
2t=x
path difference cos x
circular fringe
constant
Parallel reflecting surfaces Extended source
Division of Amplitude
Localized at infinity
Fringes of equal inclination
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Oxford Physics: Second Year, Optics
Wedged Parallel
Point
Source
Non-localised
Equal thickness
Non-localised
Equal inclination
Extended
Source
Localised in plane
of Wedge
Equal thickness
Localised at infinity
Equal inclination
Summary: fringe type and localisation