Transcript Slide 1

Building and Testing a Laser Balance Detector
David Grayson ([email protected])
University of Illinois at Urbana-Champaign and University of Rochester
Table top test of general relativity
Dispersive medium + gravity + light => phase shift [1].
Balance detectors are simple to build
Laser, Intensity I1
Ideal Balance
Detector: Voltage = 0
if and only if intensities
are equal.
Dr. John Howell’s group @ University of Rochester:
Sagnac interferometer + dispersive slow-light medium in one
arm  measure phase shift.
Control beam and balance detector used to minimize
mechanical fluctuations.
Other balance detector measures phase shift of signal beam.
Procedure: Make
voltage zero.
Measure intensities.
[1] S. Manly and E. Page, Phys. Rev. D 63, 062003 (2001)
Balance detectors measure laser
beam intensity difference
Intensity I2
-15 V
Laser beams (same color)
0V
+15 V
Intensity I1
Input Power
Output: Voltage V proportional to (I1-I2)
(up to ±15V)
Response near zero test
Laser, Intensity I2
Voltage V proportional to (I1-I2)
(up to ±15V)
Sensitivity test
Ideal Balance Detector:
Voltage(I1, I2) = k(I1 – I2)
Real Results:
Detectors behave linearly.
Sensitivity k ~ .25 V/µW.
Results: Detectors can measure differences as small as
2µW as long as average intensity is less than 120µW.
Conclusions
Five detectors were built and tested. Two are now being
used in the experiment.
Acknowledgments
My Advisor: Professor John Howell. Program
Coordinator: Connie Jones, John Gresty, David Starling,
Ben Dixon. The Research Experience in Physics and
Astronomy for Undergraduates at the University of
Rochester, funded by National Science Foundation
Grant No. PHY-0552695.