Thanks for responding Zarqon! So if I understand correctly, you're saying that measuring for longer times will typically result in a measured linewidth that is bigger than what you would measure if you averaged for a shorter time?
I am trying to measure the linewidth of a diode laser using the self-heterodyne technique. The laser specs says that the linewidth is ~100kHz at 1us. I guess I am confused by the "at 1us" and how exactly that translates to measuring the linewidth myself by looking at the beat note on a spectrum...
If the limits of integration of my integral are from -Infinity to zero, can I change those limits such that they're from zero to +Infinity? If so, how?
Thanks!