Equipment and Methods

For this lab we used a Photomultiplier Tube (PMT), a dark box, and an LED light. The PMT itself is a very sensitive instrument that is used to detect individual photons from a light source. The light source, in this case, was an LED light. We were able to vary the intensity of the LED to control the average number of photons being sent into the PMT. Due to the sensitivity of the PMT, the device needed to be enclosed in a dark box along with other light reducing materials to ensure minimal exposure to outside light sources that could damage the device. The PMT works on a basis similar to that of the photo-electric effect. The incoming photons strike a photoemissive diode which emits electrons due to the photo-electric effect. These electrons are then accelerated through additional electrodes which affectively amplify the initially low signal, allowing for it to be collected at the final anode to be measured. All of this is attached to a local SUN workstation which provides us access to the digitized PMT data.

Various samples of data were gathered from the PMT at different rates. We had control over how bright the LED source was, how many samples we were collecting for each data set, and the rate at which the PMT would collect data¹. We can calculate the time interval, in seconds, that the PMT was active for during each experiment by taking the inverse of the rate ( $t=\frac{1}{rate}$). For example, a rate of 1000 Hz corresponds to 1 millisecond. The data acquired was then read into IDL where we created histogram plots. We used these plots to analyze some of the statistical properties of the light we were receiving from the LED. The data for this lab was gathered by myself on two separate days. The first set of data was gathered on September 4, 2006. The second set was gathered on September 8, 2006.