Building and Testing a Laser Balance Detector David Grayson (email@example.com) University of Illinois at Urbana-Champaign and University of Rochester. Table top test of general relativity. Balance detectors are simple to build. Response near zero test.
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University of Illinois at Urbana-Champaign and University of Rochester
Table top test of general relativity
Balance detectors are simple to build
Response near zero test
Dispersive medium + gravity + light => phase shift .
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
Other balance detector measures phase shift of signal beam.
 S. Manly and E. Page, Phys. Rev. D 63,062003 (2001)
Laser, Intensity I1
Ideal Balance Detector: Voltage = 0
if and only if intensities are equal.
Procedure: Make voltage zero.
Results: Detectors can measure differences as small as 2µW as long as average intensity is less than 120µW.
Voltage V proportional to (I1-I2)
(up to ±15V)
Balance detectors measure laserbeam intensity difference
Laser, Intensity I2
Five detectors were built and tested. Two are now being used in the experiment.
Ideal Balance Detector:
Voltage(I1, I2) = k(I1 – I2)
Detectors behave linearly.
Sensitivity k ~ .25 V/µW.
Laser beams (same color)
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.
Output: Voltage V proportional to (I1-I2)
(up to ±15V)