Building and Testing a Balance Detector

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Building and Testing a Balance Detector

• David Grayson University of Illinois at
  Urbana-Champaign davidegrayson_at_gmail.com
• Prof. John Howell University of Rochester
• Research Experience in Physics and Astronomy for
  Undergraduates at the University of Rochester

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Balance detectors measure laser beam intensity
difference
Input Power
Intensity I2
-15 V
Laser beams (same color)
0 V
Intensity I1
15 V
Output Voltage propotional to (I1-I2) (up to
15V)
Voltage is 0 when I1I2
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Balance detectors are useful

• Prof. Howells lab A novel new experiment to
  test general relativity on the tabletop
• David Starling
• Manuel Alves
• Prof. Howells dream

Manny
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Our balance detectors are simple
Original detector built by Michael Pack
Circuit diagram obtained by examination.
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I built two balance detectors
BD1
BD2
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I tested the balance detectors
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The balance detectors were sensitive enough
Sensitivity Slope .27 V/µW
Sensitivity Slope .24 V/µW
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Response near zero
intensity
intensity
sensitivity
output voltage
V k(I1 I2)
Procedure
Too hard

• Adjust the system to make I1 I2
• Measure V

• Adjust the system to make V 0
• Measure I1-I2

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The balance detectors response near zero was good
Result Imbalances of 1 µW are detected in the
15-200 µW range.
Result Imbalances of 1 µW are detected in the
15-200 µW range.
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Now the balance detectors are being used in the
experiment.
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Acknowledgments

• My Advisor Professor John Howell
• Program Coordinator Connie Jones
• The Research Experience in Physics and Astronomy
  for Undergraduates at the University of
  Rochester, funded by National Science Foundation
  Grant No. PHY-0552695.
• John Gresty
• David Starling
• Ben Dixon

Questions? Contact David Grayson,
davidegrayson_at_gmail.com
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Here be dragons
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I made a quick prototype

• Used only equipment that I found in the lab

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The prototype was sensitive enough
Sensitivity Slope .26 V/µW