Transcript Polar bear fiber optics, twenty years later:

Physics research:
Interesting questions,
Interesting Independent Lab projects
Daniel W. Koon
Spring 2005
Goals of this talk
• Describe some general subtopics of physics
– Solid State physics
– Optics
• Describe some interesting research
questions, including my own research
• Suggest some Independent Lab project ideas
Structure of this talk
• Solid state physics
– Research areas
– project ideas
• Optics
– Research areas
– project ideas
• Miscellaneous project ideas
Solid state physics: charge transport
Charge transport:
• the measurement of resistivity and Hall effect
• a “cheap sub-atomic microscope”
A “cheap sub-atomic microscope”: How so?
• It’s cheap
• It explores how the molecules of the material
treat their electrons
Resistivity, r
Resistance, R: measures how an object resists
the flow of current
Resistivity, r : measures how a material resists
the flow of current
So,
(SAT flashback)
r : R = Density : mass
r = G(size,shape)  R
The Hall coefficient: the other charge
transport quantity
The Lorentz force:
  
F=qvB

 
F = qv  B
Gives rise to a Hall voltage
RH IB
VH =
t
(The Hall effect is the bending of current due to
a magnetic field.)
Punchline: charge transport as a
cheap subatomic microscope
Since
r=
RH =
1
nq
r=
1
nq
RH =
1
nq
1
nq
we can deduce the microscopic quantities by
n=
1
qR H
=
1
nqr
Koon’s solid state interests
I. The phenomenology of charge transport
measurement:
Error analysis: What do you measure when you
measure r, RH?
Is there a best sample shape?
Error analysis: How to do it
• Using computer to model current flow in the
specimen
– To compare different geometries
– To test effects of thickness
• Using a discrete-resistor model in the
laboratory
– To test linearity of the effect
Koon’s solid state interests
II. Applying charge transport measurement to specific
materials:
Hydrogen absorption in rare-earth/Pd bilayers
Challenges:
•
Rare earths corrode in O2.
•
Pd overlayer stops corrosion, allows H2 absorption.
•
Pd is a much better conductor.
•
So, how do you measure the properties of just the
RE?
Interesting Solid State questions
Is the effect of resistive inhomogeneities linear? Is it
additive (If I poke twice as big a hole in a film does it
produce twice the effect?)
Can we simultaneously measure the resistivity and
transmittance of a hydriding or corroding film?
[How] does the resistivity, Hall coefficient of a material
change as it freezes/thaws?
Optics: Biomaterials and more
Photonic Polar bears?
Solar efficient butterflies?
Ulexite (“TV rock”)
Scarlet macaws
The hairs of the polar bear are transparent light pipes that
direct ultraviolet light to its skin -- which is guess what
color? Black! So what’s white and black and warm all
over? A polar bear under the arctic sun.
Paul G. Hewitt, Conceptual Physics, 6th Edition, 1989,
p. 501
“Aristotle maintained that
women have fewer teeth than
men; although he was twice
married, it never occurred to
him to verify this statement by
examining his wives’ mouths.”
Bertrand Russell
Optical attenuation spectrum:
polar bear hair
FOUL(UP):
A Fiber-Optic Ursine Link (Universal Prototype)
for telecommunications
D. W. Koon and C. L. Jahncke, Physics Dept., St. Lawrence
University
ABSTRACT:
We have constructed what we believe is the first prototype
of a fiber-optic link to use the hair of an Arctic mammal.
The potential advantages of ursine fiber technology over
conventional technology are discussed.
http:// it.stlawu.edu/~physics/clj/foulup.html
Interesting Optics questions
Polar bear hairs as optical fibers?
[Reid Hutchins ’98]
Morpho butterflies: Does iridescence serve as a
solar panel or a sunblock?
[Andy Crawford ’99]
Ulexite (‘TV rock’): Is there cross talk in the
“fiber optic” bundles?
[Jay O’Brien ’98]
The scarlet macaw: Thin-film iridescence, or
diffraction grating, or what?
Miscellaneous interesting questions: