So, I learned about laser emitters and sensors a few days ago. I have a question regarding their application. If I place the laser in between a circular saw blade (the jagged edges), can I calculate the angular velocity by determining the time between each signal disruption on the Arduino?
you need a bit more info about the physical structure of your blade
Did you try a "back of the envelope" cackulation?
How many teeth? What maximum angular velocity or RPM? What do you expect the time between breaks of you beam to be?
So maybe it would work if you got the beam breaking to be dependable and consistent, but check for basic plausibility first.
It doesn't have to be a laser. An LED would likely also work. And you don't have to point it at the teeth. A reflective spot on the blade near the hub would work with a reflective sensor (often an IR LED and matching sensor). If there is something spinning on the same shaft as the blade, that would also be a good place for a reflector that does not require re-mounting a reflector when changing blades.
Yes, of course, using a photodiode sensor with a focusing lens, and any light source. However, a fast photodiode amplifier will be required, and it will be technically difficult (that is, take some experimentation) to get a useful signal from saw blade teeth.
For a 30 tooth saw blade rotating at 4000 RPM, expect 2000 counts/second. Any Arduino can handle that count rate.
I do like the point @johnwasser makes: detect off the motor shaft, or the main body of the blade. That way you can change the blade to one with a different number of teeth and still get an accurate speed reading.