Building and Testing a Balance Detector David Grayson – University of Illinois at Urbana-Champaign – 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 Laser beams (same color) Intensity I 1 Intensity I 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 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 BD1BD2

6 I tested the balance detectors

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

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 The balance detectors’ response near zero was good Result: Imbalances of 1 μW are detected in the 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 John Gresty David Starling Ben Dixon Questions? Contact David Grayson,

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