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]
8/6/2019 GEK1532 Interaction of Light With Matter
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
8/6/2019 GEK1532 Interaction of Light With Matter
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.html8/6/2019 GEK1532 Interaction of Light With Matter
4/45
Polarization
8/6/2019 GEK1532 Interaction of Light With Matter
5/45
Example: Transmission Curves
CalColor
30 Cyan
63%
Transm.
CalColor
60 Cyan
50%
Transm.
8/6/2019 GEK1532 Interaction of Light With Matter
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
8/6/2019 GEK1532 Interaction of Light With Matter
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
8/6/2019 GEK1532 Interaction of Light With Matter
8/45
How to produce light ?
8/6/2019 GEK1532 Interaction of Light With Matter
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/8/6/2019 GEK1532 Interaction of Light With Matter
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)
8/6/2019 GEK1532 Interaction of Light With Matter
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.
8/6/2019 GEK1532 Interaction of Light With Matter
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.html8/6/2019 GEK1532 Interaction of Light With Matter
13/45
Fluorescence lamps
collision
Emission of a
UV photon
Phosphor absorbs
UV photonEmission of visible
photon
8/6/2019 GEK1532 Interaction of Light With Matter
14/45
Fluorescence lamps
collision
Emission of
a photon
8/6/2019 GEK1532 Interaction of Light With Matter
15/45
Fluorescence lamps
http://www.astrosurf.com/buil/us/spe2/hresol4.htm
NeonMercury
8/6/2019 GEK1532 Interaction of Light With Matter
16/45
Example: Television
8/6/2019 GEK1532 Interaction of Light With Matter
17/45
Interactions of light with matter
Absorption/emission of light
absorption
8/6/2019 GEK1532 Interaction of Light With Matter
18/45
Interaction of Light with matter:
Absorption
8/6/2019 GEK1532 Interaction of Light With Matter
19/45
Interactions of light with matter
8/6/2019 GEK1532 Interaction of Light With Matter
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
8/6/2019 GEK1532 Interaction of Light With Matter
21/45
Interactions of light with matter
8/6/2019 GEK1532 Interaction of Light With Matter
22/45
A comparison of Rayleigh and Mie
scattering
from HyperPhysics by Rod Nave
Rayleigh scattering:
- wavelength dependent
- independent of particle size
(r
8/6/2019 GEK1532 Interaction of Light With Matter
23/45
Why is the sky blue?
from HyperPhysics by Rod Nave
8/6/2019 GEK1532 Interaction of Light With Matter
24/45
Why is the sky blue?
8/6/2019 GEK1532 Interaction of Light With Matter
25/45
8/6/2019 GEK1532 Interaction of Light With Matter
26/45
Interactions of light with matter
8/6/2019 GEK1532 Interaction of Light With Matter
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 )
8/6/2019 GEK1532 Interaction of Light With Matter
28/45
Is the setting sun really where you
think it is?
from HyperPhysics by Rod Nave
8/6/2019 GEK1532 Interaction of Light With Matter
29/45
The position of the sun
Refraction makes us believe that the sun is
higher in the sky than it actually is.
8/6/2019 GEK1532 Interaction of Light With Matter
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
8/6/2019 GEK1532 Interaction of Light With Matter
31/45
What is the green flash?
from HyperPhysics by Rod Nave
8/6/2019 GEK1532 Interaction of Light With Matter
32/45
Green and blue flash
light of short wavelength is refracted stronger
than light of long wavelength
8/6/2019 GEK1532 Interaction of Light With Matter
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.
8/6/2019 GEK1532 Interaction of Light With Matter
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
8/6/2019 GEK1532 Interaction of Light With Matter
35/45
Where does the rainbow come
from?
from HyperPhysics by Rod Nave
8/6/2019 GEK1532 Interaction of Light With Matter
36/45
Where does the rainbow come
from?
from HyperPhysics by Rod Nave
8/6/2019 GEK1532 Interaction of Light With Matter
37/45
Light sky below the rainbow
SUN
Observer
8/6/2019 GEK1532 Interaction of Light With Matter
38/45
from HyperPhysics by Rod Nave
8/6/2019 GEK1532 Interaction of Light With Matter
39/45
Primary rainbow
SUN
Observer
This drop reflects
red light to your eye
This lower drop
reflects blue light to
your eye
8/6/2019 GEK1532 Interaction of Light With Matter
40/45
Where does the rainbow come
from?
from HyperPhysics by Rod Nave
8/6/2019 GEK1532 Interaction of Light With Matter
41/45
Dark sky between rainbows
SUN
ObserverDrops that are higher than the drops
that cause the primary rainbow.
8/6/2019 GEK1532 Interaction of Light With Matter
42/45
Where does the rainbow come
from?
Where is the tertiary rainbow?
Higher rainbows can be observed (up to 13 orders in the laboratory with a
laser).
from HyperPhysics by Rod Nave
8/6/2019 GEK1532 Interaction of Light With Matter
43/45
from HyperPhysics by Rod Nave
8/6/2019 GEK1532 Interaction of Light With Matter
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
8/6/2019 GEK1532 Interaction of Light With Matter
45/45
Summary: Interactions of matter
with light
Color temperature
Specular reflections
Diffuse reflections
Scattering (Rayleigh and Mie)
Refraction
Absorption
Interference
Diffraction