gek1532 interaction of light with matter

8/6/2019 GEK1532 Interaction of Light With Matter

1/45

GEK1532

Interaction of Light with matter

Thorsten Wohland

Dep. Of ChemistryS8-03-06

Tel.: 6516 1248

E-mail: [email protected]


2/45

A short revision

Light is an electromagnetic wave

Light has a wavelength ( ), frequency ( ), anda polarization.

It propagates in straight lines with a maximumspeed ofc

0

Its energy depends on the frequency (E=h )and comes in small packets

The color we perceive depends on thewavelength (or rather the energy of the photons)

Light has a polarization


3/45

The electromagnetic spectrum

400 nm 500 nm 600 nm 700 nm

=0

c

http://www.olympusmicro.com/primer/java/electromagnetic/index.html
http://www.olympusmicro.com/primer/java/electromagnetic/index.htmlhttp://www.olympusmicro.com/primer/java/electromagnetic/index.html


4/45

Polarization


5/45

Example: Transmission Curves

CalColor

30 Cyan

63%

Transm.

CalColor

60 Cyan

50%

Transm.


6/45

Metamerism

Mixture of monochromatic yellow (580 nm)

and monochromatic blue (480 nm) looks

like white light to us.

http://www.crslight.com/pages/lightingcharts.htm

wavelengthrelativ

e

intensity


7/45

Color under different illumination

What happens if we illuminate an object with non-white light?

Inte

ns

ity

-

=

Inte

ns

ity

Ab

sorp

tion

-

=

Ab

sorp

tion

Inte

ns

ity

Inte

ns

ity

Inte

ns

ity


8/45

How to produce light ?


9/45

Color temperature

12,000 K

6,000 K

3,000 K

The Color of Stars

[ ]KmT

= 2898

max

http://micro.magnet.fsu.edu/primer/java/colortemperature/

Color temperature is independent of composition!
http://micro.magnet.fsu.edu/primer/java/colortemperature/http://micro.magnet.fsu.edu/primer/java/colortemperature/http://micro.magnet.fsu.edu/primer/java/colortemperature/


10/45

Incandescent light: light bulb

450 550 650

in nm

http://www.crslight.com/pages/lightingcharts.htm

http://www.astrosurf.com/buil/us/spe2/hresol4.htm

For more information on lightsources see Chapter 1 (Falk)


11/45

The structure of matter

Electrons around a nucleus (protons and neutrons) can

populate only very well defined energy levels (depicted as

circles in the above picture).

In molecules many atoms combine and share some of theirelectrons. Again the energy levels they can populate are

discreet.


12/45

The structure of matter

Absorption of energy

By collisions with other particles

By absorption of light

http://www.olympusmicro.com/primer/java/fluorescence/exciteemit/index.html

Electrons can change the energy level by absorbing just the right energy

to go to a higher level, or by emitting energy of just the right amount to

come to a lower level.

E1 E2

E1, E2: correspond to just the right energy between two levels.This energy that can be thus absorbed corresponds to a certain color.
http://www.olympusmicro.com/primer/java/fluorescence/exciteemit/index.htmlhttp://www.olympusmicro.com/primer/java/fluorescence/exciteemit/index.html


13/45

Fluorescence lamps

collision

Emission of a

UV photon

Phosphor absorbs

UV photonEmission of visible

photon


14/45

Fluorescence lamps

collision

Emission of

a photon


15/45

Fluorescence lamps

http://www.astrosurf.com/buil/us/spe2/hresol4.htm

NeonMercury


16/45

Example: Television


17/45

Interactions of light with matter

Absorption/emission of light

absorption


18/45

Interaction of Light with matter:

Absorption


19/45



20/45

Reflections

Specular reflection

(mirror like)

Incidence angle is equal to

angle of reflection: =

Diffuse reflection

Does carry not much color

information More color information


21/45



22/45

A comparison of Rayleigh and Mie

scattering

from HyperPhysics by Rod Nave

Rayleigh scattering:

- wavelength dependent

- independent of particle size

(r


23/45

Why is the sky blue?



24/45

Why is the sky blue?


25/45


26/45



27/45

Refraction

n1 n2

n1 < n2

n1 n2

n1 > n2

Snells law: The difference between and is the bigger, the bigger thedifference is between n1 and n2.

(n1sin = n2sin )


28/45

Is the setting sun really where you

think it is?



29/45

The position of the sun

Refraction makes us believe that the sun is

higher in the sky than it actually is.


30/45

Refraction

n1 n2

n1 < n2

The refractive index n is dependent on the wavelength. Usually the refractive

index increases with decreasing wavelength (normal dispersion).

n1 n2

n1 > n2


31/45

What is the green flash?



32/45

Green and blue flash

light of short wavelength is refracted stronger

than light of long wavelength


33/45

Green and blue flash

Does scattering happen as well?

Yes, so the blue light will be less intense than the

green and the green will be less intense than

the red.


34/45

Yellow Sun, Blue Sky, Red sunset

1.

2.

3.

light of short wavelength is scattered stronger

than light of long wavelength

Sun looks yellow

Sky looks blue

Sun looks red


35/45

Where does the rainbow come

from?



36/45


from?



37/45

Light sky below the rainbow

SUN

Observer


38/45



39/45

Primary rainbow

SUN

Observer

This drop reflects

red light to your eye

This lower drop

reflects blue light to

your eye


40/45


from?



41/45

Dark sky between rainbows

SUN

ObserverDrops that are higher than the drops

that cause the primary rainbow.


42/45


from?

Where is the tertiary rainbow?

Higher rainbows can be observed (up to 13 orders in the laboratory with a

laser).



43/45



44/45

Refraction

n1 n2

n1 < n2

The refractive index n is dependent on the wavelength. Usually the refractive

index increases with decreasing wavelength (normal dispersion).

n1 n2

n1 > n2


45/45

Summary: Interactions of matter

with light

Color temperature

Specular reflections

Diffuse reflections

Scattering (Rayleigh and Mie)

Refraction

Absorption

Interference

Diffraction

gek1532 interaction of light with matter

Documents