In the example sketched above, the laser pulses seven times as the slit traverses it. The beam profiler software connects the dots by looking at the peaks, and estimates the “CW profile.” As you can imagine, the more pulses in that profile, the better the software can estimate the real profile, giving a more accurate beam width result.
As a rule of thumb, the minimum number of pulses you need for one profile is about 8-10, while 15 pulses are required to achieve 2% accuracy.
There’s one more caveat: if you want to calculate the slit speed directly from the drum speed, you need to account for the angle of rotation (45°). Therefore the actual speed of the slit across the laser beam is the drum speed divided by √2 .
The following equation takes laser pulse frequency and number of pulses per profile as given parameters to calculate the minimum laser beam diameter: