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.
Equipment and Methods
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 (
). 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.