Laser Beam Blocker The purpose of the Beam Blocker is to block the laser if the PMT (photo multiplier tube) is receiving too much light. The beam blocker is constructed with a weighted aluminum disk, small solenoid, and a timer. In the experiment a laser is shot through the beam blocker and then a polymer melt. The scattered light is detected using a PMT. If a bubble or a dust particle in the polymer drifts into the laser path the scattered light can become intense enough to damage the PMT. The output of the PMT is monitored on a computer as part of the data-collection program. If the counts get to high a single character is sent out the serial port. This triggers a timer that energizes the solenoid for about four seconds. The solenoid pulls in the pin allowing the wheel to turn (due to extra weight on one side of the wheel) and block the laser. It must me manually reset. The Beam Blocker is currently being used in Dr. Selsers Lab