Light: Basic principles

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Light: Basic principles

Dr Yoonchan Jeong

School of Electrical Engineering, Seoul National University

Office: 302-523 (temporary), Tel: +82 (0)2 880 1623, Fax: +82 (0)2 873 9953 Email: [email protected]

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2

n = 1.406 (centre) n = 1.386 (edge)

n = 1. 337

n = 1. 336

Human eyes are not like a monochrometer!

Not everyone sees the same colours!

Eye optics degeneracy, variations in cone pigments, and different

psychological experience

Retina photoreceptors:

• Cones (s, m, l): sensitive to colours

• Rods: not sensitive to colours, dark- adapted

s m l

Visible: 400 ~ 700 nm

Human eye & colour vision

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• Photopic vision:

– Perceived brightness with colours (cones)

– Most sensitive at 555 nm:

683 lm/W

– Perceived brightness is different with colours even with the same optical power!

– More important to displays

• Scotopic vision:

– Dark adapted (rods)

– Most sensitive at 507 nm:

1700 lm/W

Brightness perception

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Laser safety

CLASS 1 LASER PRODUCT LASER RADIATION

DO NOT VIEW DIRECTLY WITH OPTICAL INSTRUMENTS CLASS 1M LASER PRODUCT

LASER RADIATION

DO NOT STARE INTO BEAM CLASS 2 LASER PRODUCT

LASER RADIATION

DO NOT STARE INTO BEAM OR VIEW DIRECTLY WITH OPTICAL INSTRUMENTS CLASS 2M LASER PRODUCT

LASER RADIATION

AVOID DIRECT EYE EXPOSURE CLASS 3R LASER PRODUCT

LASER RADIATION

AVOID EXPOSURE TO BEAM CLASS 3B LASER PRODUCT

LASER RADIATION

AVOID EYE OR SKIN EXPOSURE TO DIRECT OR SCATTERED RADIATION CLASS 4 LASER PRODUCT

e.g. 0.39 mW @600 nm

1 mW @400 - 700 nm

0.5 W 5 mW

all lasers with beam power higher than class 3B

Protective eyewear required !

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 Frequency

(Hz)

 Wavelength

(m)

1THz

1GHz

1MHz

1kHz

21cm H line

h

Photon energy (eV)

1MeV

1keV

h

Photon energy

(J)

-RAYS

X-RAYS ULTRAVIOLET

10^20

10^27

1022

101 4

101 2

109

106

103

106

103

101

106

101 1

LIGHT INFRARED

MICROWAVES

RADIOFREQUENCY

UHF VHF TV

Radar FM Radio Broadcast

Power Lines

Outer electrons Eye Arcs

1eV ₁₀⁰ 1nm 1Å

1cm 1m

1km 10^13

10^10

10^9

10^2

100

102

103

105

1mm ₁₀^⁶

101 5 ₁₉

10^ 10^18

10

10^14

MICROSCOPIC

SOURCE DETECTION

ARTTIFICIAL GENERATION Atomic

nuclei Inner electrons Inner and Outer electrons Molecular vibrations

and rotations Electron spin

Nuclear spin

Geiger and scintillation Ionization

chamber Photoelectric Photomultiplie

r Bolometer Thermopile

Crystal Electronic

circuits

Accelerators X-ray tubes Synchrotrons

Lasers Sparks Lamps Hot bodies Magnetron Klystron Travelling-wave

tube Electronic

circuits AC generators

Electromagnetic-Photon Spectrum

Visible Light (400 nm ~ 700 nm)

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Maxwell’s Equations

 Maxwell’s Equations

 Constitutive Equations

0













 

 





 

 





B D

D J H

E B

 t

t

Faraday’s law Ampère’s law Gauss’s law

No free magnetic monopole (?)

M H

H B

P E E

D









o o

m m



 (   

_o

n

²

, m  m

_o

)

Isotropic and non-magnetic

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Wave Equations

 Wave Equations

 Plane Wave

 Phase Velocity

0 ,

0 ₂

2 2

2 



 



 

 

 t t

H H

E m E m (Homogeneous and no source)

m



 eⁱ⁽^^t^^k^^r⁾, k 

s m c

t k

o o

/ 10 997930

. 1 2

1 , v

constant,

8 p









 m

m

 k r 

) ,

( ) , ( .

.g f x t f x x t t

e   

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Boundary Conditions

 Continuity Relations

0













 

 





 

 





B D

D J H

E B

 t

t

Tangential Comp.

Normal Comp.

K H

H

n( ₂  ₁) 







(D₂ D₁) n

0 ) ( ₂  ₁ 

 B B n

0 ) ( ₂  ₁ 

 E E



n



 

1 2

n

1 2

C

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Reflection and Refraction

E_i H_i k_i

E_r H_r

k_r q_i q_r

q_t E_t H_t k_t

Plane of Incidence n_i

n_t

H_i E_i k_i

H_r E_r

k_r q_i q_r

q_t H_t E_t k_t

Plane of Incidence n_i

n_t

 P-Polarization (TM)  S-Polarization (TE)

 Snell’s Law

t t

i

i n

n sin

q

 sin

q 

Field continuity of tangential components

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0 10 20 30 40 50 60 70 80 90 0.0

0.2 0.4 0.6 0.8 1.0

n_i < n_t

n_i = 1, n_t = 1.5 P-Polarization S-Polarization

Reflectivity

Incident Angle q_i [deg]

Brewster

angle ⁰ ¹⁰ ²⁰ ³⁰ ⁴⁰ ⁵⁰ ⁶⁰ ⁷⁰ ⁸⁰ ⁹⁰

0.0 0.2 0.4 0.6 0.8 1.0

n_i > n_t

n_i = 1.5, n_t = 1 P-Polarization S-Polarization

Reflectivity

Incident Angle q_i [deg]

Critical angle

Brewster Angle and Critical Angle

 Brewster Angle  Critical Angle

 Reflectivity

) ( tan

¹

i t

B

n



n q 

2

q 

q

_i  _t 



) ( sin

¹

i t

c

n



n q 

,

q





2

 _t _t

i n



n

For P-polarization Total internal reflection

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Polarization and Anisotropy

 Constitutive Relation for Electrical Field

P E E

D 







_o 



























Biaxial Uniaxial

Isotropic

n n

n

n n

n

n n

n

n n

n

z y

x

z y

x

z y

x

z y

x o

2 2

2

0 0



with

 k Surface  Index Ellipsoid  Double Refraction

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Dispersion

 Natural Dispersion RAINBOW

White light

Prism

 Material Dispersion

White light which is a mixture of colors is separated into its different wavelengths.

Refractive index

n

is inherently a function of wavelength.

Recall Snell’s law!

t t

i

i n

n sin

q

 sin

q

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Scattering

 Rayleigh Scattering

- When an electromagnetic radiation hits a particle whose diameter is smaller than the wavelength of the radiation

- Short wavelength is scattered more than long wavelength

 Mie Scattering

- When an electromagnetic radiation hits a particle whose diameter is similar or greater than the wavelength of the radiation

- Roughly independent of wavelength

 Phenomenon

- Interaction between an electromagnetic radiation and small particles or molecules

- Different wavelengths get

deflected in different directions.

4

~ 1



Source: http://www.vislab.usyd.edu.au/photonics/

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Scattering

Rayleigh scattering Mie scattering

No scattering

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Diffraction and Interference

 Diffraction

A wave such as light is bent when it passes an edge or through an

aperture. The aperture or the edge acts as a radiating point (Huygens–

Fresnel principle).

This effect increases as the physical dimension of the aperture is close to the wavelength of the wave.

 Constructive Interference

 Destructive Interference

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Interference by Multiple Reflection

 Fabry-Perot Interferometer

 q m nd cos  2

Constructive interference (100 % transmission)

