Say it with Microwaves:
The SLU Microwave Optics
Symposium
Daniel W. Koon
St. Lawrence University Physics Dept.
dkoon@stlawu.edu
To find this talk online, Google the phrase, “Say it with microwaves”.
It is the only hit. (Updated version: next week)
Contents
• The SLU MW Optics
Symposium [SLU-MOS]
– History
– What it is
– Role in Physics Curriculum
• Improvements to the MW Lab
– Novel prism design
– Detector calibration
– New experiments
ZooAve
La Garita, CR.
History of SLU-MOS
• MW Equipment purchased with
US National Science
Foundation grant, 1989.
• Symposium launched shortly
afterwards.
• SLU-MOS forms part of
sophomore (2nd) year physics
lab curriculum.
Zoo Ave
La Garita, CR
SLU-MOS: What is it?
• Students spend 2-3 weeks on Microwave
Optics experiments
• Individualized experiments
• Shared basic equipment, physics
• Students present their “research” as
physicists do:
• Formal written lab report
• Formal oral presentation to other students,
faculty.
MOS as ‘bridge’ within SLU
Physics major
• Lab curriculum
– Bridge between week-long,
“cookbook” experiments to longer,
experiments requiring student design
• Communications skills
– Bridge between University-wide FirstYear Program and Physics Dept.
Senior Thesis defense
• Modern Physics lecture course
– What does it mean to test the wavelike properties of electrons, photons,
X-rays, gamma rays, etc.?
Church, ca. 1693
Ujarras, CR
Impact of MOS on Department
• Improvement in senior theses (both
written and oral versions)
• Better awareness of need to integrate
teaching communications skills within
major
Zoo Ave
La Garita, CR
• 2 weeks of experiments sacrificed for
communications workshops during
semester
• Workshop on formal lab reports
• Workshop on oral presentation
Pasco Scientific
Microwave Optics System
• Common hardware
– 10.5 GHz source, detector
– Mounting hardware, incl.
goniometer.
– Aluminum “mirrors”/blocks
– “Half-silvered” mirrors
• Experiment-specific hardware
–
–
–
–
Bragg cube
Prism form
Polarizers
Dielectric slab
Pasco Scientific’s Advanced
Microwave Optics System. WA
9316. www.pasco.com.
Standard Pasco experiments in
Microwave Optics
Physical Optics
Other phenomena
Standing waves
Polarization (Malus’ law)
Double slit
Fiber optics
Lloyd’s mirror
Refraction (Snell’s law)
Fabry-Perot interferometer
Brewster’s angle
Michelson interferometer
Bragg diffraction
Microwave Optics prisms
Pasco Scientific’s prism form.
Just add polystyrene pellets. User is
restricted to only two values of incident
angle, one of which produces total
internal reflection. www.pasco.com
Variable-angle prism form.
After Albiol, F., Navas, S. and
Andres, M. V., Am. J. Phys. 61,
165–169 (1993). Pellets inserted
into gray region. Pellet spills a
problem.
Microwave Optics prisms:
The hemicylindrical prism
Hemicylindrical prism for investigating Snell’s Law. Unlike Pasco’s prism
form, allows for a large range of incident angles. Provides for ease of use
relative to the variable-angle prism form of Albiol et al, and allows for the use
of other materials. Can be made of solid material (paraffin at right), or as form
to be filled with pellets (cardboard at right).
Applications:
Hemicylindrical MW Prism
• “Microwave Tunneling”. [Albiol et
al., 1993]
– Frustrated Total Internal Reflection.
– Optical analogue for Quantum
Mechanical Tunneling.
• Snell’s Law.
– Measure qt for a variety of qi.
– Plot sinqt vs sinqi. Slope = 1/n.
Coati (pizote),
Monteverde
Applications:
Hemicylindrical MW Prism
Calibrating microwave detectors
• Detector measures arbitrary signal:
– not E-field magnitude, E
– not intensity, IE2
– not a power of either I or E.
• [despite Combes, P. F., Graftenil, J., and Santereau, J. F.,
Microwave Components, Devices and Active Circuits
(Wiley, New York, 1987), cited in Albiol et al., op cit.]
– At best, a power law with a variable exponent.
(curved line in a log-log plot)
Calibrating microwave detectors
Microwave Intensity vs Signal for Detector 411
Collected Data
Calibration Data
1
0.01
0.1
1
10
100
Intensity (arb. units)
0.1
0.01
0.001
0.0001
Signal x Multiplier (Volt)
Ciesla, Stephen, “Beer’s Law”, SLU-MOS 2005, unpublished.
Calibrating microwave detectors
• For many experiments, this is not a problem.
–
–
–
–
Double-slit interference
Fabry-Perot interferometer
Bragg scattering
Snell’s law
• For others, it is:
– Single-slit diffraction
– Beer’s law for absorption
 a

I (q )  I 0sinc  sin q 


I ( x)  I 0 e x
2
Malus’ Law
• Intensity of MWs passing
through tilted polarizer.
I (q )  I 0 cos 2 q
• Measured intensity when
MW emitter, detector
tilted relative to each
other. Provides a way of
calibrating MW detector.
Malus’ Law for calibration
Beer’s Law: Attenuation of MWs in water
Ciesla, Stephen, “Beer’s Law”, SLU-MOS 2005, unpublished.
Applications of MW detector
calibration via Malus’ Law
• Beer’s Law.
• Expand Pasco’s Fiber optic
experiment to test whether
wave profile is Gaussian.
• Expand Pasco’s “Brewster’s
Angle” experiment to test
Fresnel Equations for reflection
at incident angles, qi.
Barva, Heredia
New experiments
• Beer’s Law.
– Measure attenuation of intensity as microwaves travel
through suspended wet paper towels.
• Microwave Lenses.
– Interference clearly visible on top of geometric optics.
• Beat patterns.
– Typical Df ≤ 10MHz out of 10.5GHz.
• Multiple thin-film interference.
– Multiple-dielectric stack shows effects of both
geometrical optics, physical optics.
New
Experiments:
Beat patterns
•10.53GHz typical
•15MHz variation
among sources
•2MHz “tunability” of
each source.
New experiments:
Multiple thin-film interference
Conclusions
• A symposium in Microwave Optics serves as
opportunity to develop student
– research skills
– oral and written communications skills
• Pasco MW Optics equipment can be improved via
– Hemicylindrical prism
– Detector calibration à la Malus
• Other MW Optics experiments can be added to
standard repertoire associated with this equipment.