Download Light Sources and Interaction of Light With Matter

“Light Sources and Interaction of
Light With Matter”
IST 8A Lecture #3 - Jan. 12, 2005
M. Molinaro, F. Chuang
IST 8A (Shedding Light on Life) - W05
Lawrence Livermore
National Laboratory
Sources of Light
 What
do you think are some of the
sources of light?
Sources of Light
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Incandescence:
Incandescence: light emission by thermal radiation of a temperature high
enough to render the source of radiation visible.
Electroluminescence:
Electroluminescence: light-emitting diode (LED)
Laser:
Laser: light amplification through the stimulated emission of radiation
Fluorescence:
Fluorescence: light emission resulting from absorption of shorter-wavelength
electromagnetic radiation. Persists for less than 10-8 sec after excitation.
Phosphorescence:
Phosphorescence: similar to fluorescence, but persisting longer than 10-8 sec
following excitation.
ChemiChemi- and Bio-luminescence:
Bio-luminescence: e.g., the firefly
Blackbody radiation:
radiation: “pure”
pure” form of incandescence
Sources of Light - Incandescence
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What is it and how does it work? Incandescence
Incandescence is the release of
electromagnetic radiation from a hot body due to its high temperature. The
release of radiation is usually in the infrared (heat
(heat)) and the visible region of the
electromagnetic spectrum (we perceive as light.) Incandescence occurs in both
light bulbs where the electrical resistance to electron flow excites electrons in
the material to jump to a higher orbit, and thus subsequently release a photon;
and when something is on fire or during an explosive or a combustion reaction.
X-rays can also be produced by incandescence, but often most energy is
wasted in the form of heat. Tungsten bulb glows at 2700K.
Range of wavelengths produced IR and visible
Energy efficiency: about 90% given off as heat
http://en.wikipedia.org/wiki/Incandescence
http://en.wikipedia.org/wiki/Incandescent_light_bulb
http://www.gwebdesign.de/company-en.html
Sources of Light - Electroluminescence
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What is it and how does it work? Electroluminescence is an optical
phenomenon and electrical phenomenon where a material such as a natural
blue diamond emits light when an electric current is passed through
it.Electroluminescence (EL) is mainly observed in semiconductors.
semiconductors. The electric
field excites electrons in the material which then emit the excess energy as
photons. LEDs are the most well known example of electroluminescence.
Range of wavelengths produced (LED) is a semiconductor device that emits
incoherent monochromatic light.
light. The wavelength of the light emitted depends
on the bandgap energy of the materials forming the pn junction. The materials
used for an LED have bandgap energies corresponding to near-infrared, visible
or near-ultraviolet light.
Energy efficiency: 2 to 4 times more efficient than incandescent - less heat!
Demo:
RGB LED
http://www.kolej.pl/modele/JTZ/obwody/swiatlo.html
http://en.wikipedia.org/wiki/Electroluminescence
http://en.wikipedia.org/wiki/LED
http://www.fortrantraffic.com/signals/led/LED.htm
Sources of Light
LASER = Light Amplification through Stimulated
Emission of Radiation
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Monochromatic
Coherent
http://science.howstuffworks
.com/laser.htm
htm
http://science.howstuffworks.com/laser.
Directional
Can focus to few hundred nm, high power
Range from UV to Visible to IR + some are tunable
Can pulse down to femtoseconds
http://en.wikipedia.org/wiki/Laser
Sources of Light
How a Ruby Laser Works
1. Ruby laser in nonlasing state
2. Light flash excites
atoms in the ruby rod
3. Excited atoms emit
photons in random
directions
4. Photons traveling
parallel to rod axis get
reflected back and
forth, exciting more
atoms in the process
5. Monochromatic,
coherent, directional
laser beam exits from
partially mirrored
surface
Sources of Light - Fluorescence
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What is it and how does it work? Fluorescence is the property of some atoms
and molecules to absorb light at a particular wavelength and to subsequently
emit light of longer wavelength after a brief interval, termed the fluorescence
lifetime. The process of phosphorescence occurs in a manner similar to
fluorescence, but with a much longer excited state lifetime
Range of wavelengths produced Usually the fluorescent materials are
“excited”
excited” by shining UV light and they re-emit in the visible and infra-red.
Energy efficiency: 4 times more efficient than incandescent. Low heat!
Inside the glass tube is a partial vacuum and a small
amount of mercury. An electric discharge in the tube
causes the mercury atoms to emit light. The emitted light is
in the ultraviolet range and is invisible, and also harmful to
living organisms, so the tube is lined with a coating of a
fluorescent material, called the phosphor, which absorbs
the UV and re-emits visible light.
http://en.wikipedia.org/wiki/Fluorescence
http://www.geology.wisc.edu/~museum/old/whatis3.html
Sources of Light - Fluorescence
http://micro.magnet.fsu.edu/primer/lightandcolor/fluorointroduction.html
http://www.bris.ac.uk/Depts/Synaptic/info/imaging/imaging_1.htm
Sources of Light - Fluorescence
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Fluorescence:
Fluorescence: light emission resulting from absorption of shorter-wavelength
electromagnetic radiation. Persists for less than 10-8 sec after excitation.
http://micro.magnet.fsu
http://micro.magnet.fsu..edu/primer/techniques/fluorescence/excitation.html
edu/primer/techniques/fluorescence/excitation.html
Sources of Light - Fluorescence
Quantum Dots
Dr. D. Talapin, University of Hamburg,
http://www.chemie.uni-hamburg.de/pc/Weller/
http://www.qdots.com/live/render/content.asp?id=84
Sources of Light - Phosphorescence
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How it works Phosphorescence is a
radiative transition involving a
change in the spin multiplicity
of a molecule. Because of this
change, the radiative transition
is delayed, and the
phosphorescent material glows
a while after the incident
illumination stops. Because of
this, phosphorescent materials
are most commonly called
"glow-in-the-dark".
http://images.iwoot.com/large/glofri_lg.jpg
http://www.valhallaarms.com/technology/lighting_fx.htm
http://en.wikipedia.org/wiki/Phosphorescence
http://www.olympusfluoview.com/theory/fluoroexciteemit.html
Sources of Light - Chemi and Bioluminescence
How it works: Chemoluminescence (sometimes
"chemiluminescence") is the emission of light
(luminescence) as the result of a chemical reaction.
Most simply, given A and B, with an excited
intermediate ◊, we have,
[A] + [B] --> [◊] --> [Products] + light
The decay of the excited state[◊] to a lower energy level
is responsible for the emission of light.
 When chemoluminescence takes place in living
organisms, the phenomenon is called
bioluminescence
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http://en.wikipedia.org/wiki/Chemoluminescence and Bioluminescence
http://www.omniglow.co.uk/inpublisher/
uploaded_images/snaplight_pk_ass.JPG
http://www.mbari.org/itd/
retrospective/bioluminescence.html
Sources of Light - Chemi and Bioluminescence
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Luminol : Luminol is used by investigators to locate blood, even if it has been
cleaned or removed. Using its natural property of chemiluminesence, it glows if
blood is present. The glow lasts for about 30 seconds and is blue. Luminol reacts
with the iron in hemoglobin, a pigment present in blood.
http://curiouslee.typepad.com/photos/best_of_curiouslee/firefly.html
http://en.wikipedia.org/wiki/Luminol
Sources of Light - Blackbody
http://en.wikipedia.org/wiki/Blackbody
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How it works: A blackbody is an object that emits a well defined spectrum of radiation
solely based on its temperature. Blackbody temperature is the temperature of an object if it
is reradiating all the thermal energy that has been added to it; if an object is not a
blackbody radiator, it will not reradiate all the excess heat and the leftover will go toward
increasing its temperature.
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Stefan-Boltzmann
Stefan-Boltzmann law - overall power emitted per unit area.
Wien’
Wien’s law - Defines strongest emission
Real objects never behave as full-ideal black bodies, and instead the emitted
radiation at a given frequency is a fraction of what the ideal emission would be.
http://www.astronomycafe.net/qadir/q72.html
Colder
Even as the peak wavelength moves into the ultra-violet enough radiation continues to be emitted in
the blue wavelenths that the body will continue to appear blue. It will never become invisible.
Hotter
Sources of Light - IR emission
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Examples
http://coolcosmos.ipac.caltech.edu/image_galleries
Demo:
Thermometer
Sources of Light - Blackbody
Interactive Applet
Blackbody
Interaction of Light with Matter
Target material
Incoming photon
?
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Q: What happens when photons hit matter..?
A: Both light and matter can be affected. Consider both
Fates of Light, and Fates of Material..!
Interaction of Light with Matter
Incoming photon
Materials with high
electron density, such
as metals (i.e., silver,
mercury, aluminum)
Reflected photon
Reflection: The return of radiation
by a surface, without change in
wavelength.
Demo: Laser reflect, measure angles
Interaction of Light with Matter
Incoming photon
Transmitted photon
Materials like water,
glass, plastic, etc…
Transmission: The conduction of radiant energy through a medium.
Interaction of Light with Matter
Materials like water,
glass, plastic, etc…
Transmitted photon
ray in the denser medium is always closer to the normal
Incoming photon
Refraction: Change in direction of a wave due
to a change in velocity..
The refractive index of a material is the factor
by which electromagnetic radiation is slowed
down (relative to vacuum) when it travels inside
the material. Glass 1.5-1.9, diamond 2.41
http://en.wikipedia.org/wiki/Refraction
Snell’s Law: n1sin(θ1) = n2sin(θ2)
Demo: Vapor chamber + plexiglas
Interaction of Light with Matter
Interactive Applet
Reflection and Refraction
Interaction of Light with Matter
Side scatter
Incoming photon
Forward scatter
Back scatter
Scattering: The change in spatial distribution of a beam of radiation when
it interacts with a surface or heterogeneous medium. The sky blue because
molecules in the air preferentially scatter blue light. Scattering varies as a
function of the ratio of the particle diameter to the wavelength of the radiation.
http://en.wikipedia.org/wiki/Scattering
Interaction of Light with Matter
Incoming photon
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Diffraction: The
T apparent bending and spreading of waves when they meet
an obstruction. Diffraction also occurs when any group of waves of a finite
size is propagating; for example, a narrow beam of light waves from a laser
must, because of diffraction of the beam, eventually diverge into a wider
beam at a sufficient distance from the laser.
Interaction of Light with Matter
Scattering Demo - tape and
plastic cup
Diffraction Demo - Light
through a slit or on a hair
Interaction of Light with Matter
Interaction of Light with Matter
http://www.olympusmicro.com/primer/lightandcolor/diffraction.htm and
http://www.olympusmicro.com/primer/java/diffraction/index.htmll
Interaction of Light with Matter
Incoming photon
Energy
Absorption: The loss of light as it passes through a material,
generally due to its conversion to other energy forms.
Transforming Energy
Thermal
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Heat
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Electrical
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Electricity
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Chemical
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Chemistry
Photonic
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Light
Kinetic
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Motion
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Interaction of Light with Biomaterials
Incoming photon
Reflection
Absorption
Transmission
Scattering
In complex materials, any combination of interactions are
possible. The exact nature of each process depends on the
physical and chemical structure of the biomaterial.