April Cools 2024: Physics Edition
This particular experiment was driven by a laser that periodically spit out pulses that were 5ns long. A photodiode would pick up when a pulse was emitted, and we'd use that as the trigger for the oscilloscope. The oscilloscope would then record signals from our two other detectors. One of these is called "probe" and the other is called "reference".
Only the beam hitting the probe detector actually passes through the sample. The beam hitting the reference detector does not pass through the sample, so any variations in intensity must come from noise in the laser, vibrations in the table, etc. All of these variations should be seen in both the probe and reference beams since they were produced by splitting a "parent" beam.
We do this so that if you divide the probe signal by the reference signal you cancel out any part of the signal that doesn't come from the physics happening inside the sample. This isn't perfect, but it works well enough.
