Physics307L:People/Ozaksut/Notebook/070912

Speed of Light

Speed of Light Lab

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Steven J. Koch 02:20, 13 September 2007 (EDT):Great work in the lab today. This is a pretty complicated setup (given the simple concept), especially since none of us really have used the NIM-bin stuff before. I think you ran out of time before recording the final stuff at the end, and it would be important to record those kind of notes right away. I will sketch out a few of them. I do realize that it's tough to take notes while you are racing to get the experiment working at all, but it's a good habit to get into. In general, the description you do have is great.

Setup

We connected the green Light Emitting Diode (LED light) to a power supply at 200V, and also to the "start" input on the Time to Amplitude Converter (TAC). Then, we connected the Photo Multiplier Tube (light detector) located at the end of a dark tube to reduce ambient light, from the anode to a delay thing and then to the "stop" input on the TAC. The polarizer on the front of the LED lets us maintain a constant amplitude (340mV) of light as we move the LED closer to the detector. We wanted to measure the LED pulse and detected pulse independently first, so we connected the LED directly to the oscilloscope and the detector to the delay and then to the oscilloscope. We kept getting fuzzy signals or weird bumps in the signals, so we added terminators to the end of the cords to try to reduce the resonance. We first had our LED set at 9m from the detector, and when we pushed it in 2m, we noticed the signal from the detector became sharper.

We decided to start from scratch to obtain more precise measurements. This time we pulled the LED to the outer edge of the tube without exposing the PMT to ambient light. We re-polarized the detector until the Oscillioscope showed a maximum amplitude of 100mV.

A few comments from Koch

1. It's not clear the delay module works. The signal straight out of PMT looks smooth, but running it through the delay module makes it wiggly as all hell.
2. As a default, if Monday people can't make more progress, some estimations of pulse delays can be made with the oscilloscope alone. However, because of the limited bandwidth of the scope, I'm not sure this is possible. Maybe if we are clever.
3. We also couldn't figure out how to get the TAC to work. It didn't seem to be responding to the "stop" signal at all (possibly because the delay module is not working)? This did seem to be working, though, for Antonio and Brian.