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. 2 Balance detectors measure laser beam intensity difference Laser beams (same color) Intensity I 1 Intensity I 2 +15 V 0 V -15 V Input Power Output: Voltage propotional to (I 1 -I 2 ) (up to ±15V) Voltage is 0 when I 1 =I 2

3. 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. 4 Our balance detectors are simple Original detector built by Michael Pack Circuit diagram obtained by examination.

5. 5 I built two balance detectors BD1BD2

6. 6 I tested the balance detectors

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

8. 8 Response near zero V = k(I 1 – I 2 ) 1.Adjust the system to make V = 0 2.Measure I 1 -I 2 1.Adjust the system to make I 1 = I 2 2.Measure V Procedure: intensity sensitivityoutput voltage Too hard

9. 9 The balance detectors’ response near zero was good Result: Imbalances of 1 μW are detected in the 15-200 μW range.

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

11. 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. 12 Here be dragons

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

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