Building and Testing a Balance Detector

1. Building and Testing a Balance Detector David Grayson – University of Illinois at Urbana-Champaign – davidegrayson@gmail.com Prof. John Howell – University of Rochester Research Experience in Physics and Astronomy for Undergraduates at the University of Rochester

2. Balance detectors measure laser beam intensity difference Input Power Intensity I2 -15 V Laser beams (same color) 0 V +15 V Intensity I1 Output: Voltage propotional to (I1-I2) (up to ±15V) Voltage is 0 when I1=I2

3. Balance detectors are useful • Prof. Howell’s lab: A novel new experiment to test general relativity on the tabletop • David Starling • Manuel Alves • Prof. Howell’s dream Manny

4. Our balance detectors are simple Original detector built by Michael Pack Circuit diagram obtained by examination.

5. I built two balance detectors BD1 BD2

6. I tested the balance detectors

7. The balance detectors were sensitive enough Sensitivity = Slope = .27 V/μW Sensitivity = Slope = .24 V/μW

8. Response near zero output voltage sensitivity intensity intensity 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

9. 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.

10. Now the balance detectors are being used in the experiment.

11. 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@gmail.com

12. Here be dragons

13. I made a quick prototype • Used only equipment that I found in the lab

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