While doing an experiment to measure the angular spread (or say divergence) of a beam of laser (which in my case was an inexpensive diode laser), what is the most accurate way of measuring the diameter of the beam?
Angular spread, $θ$ = $d'/l$ where $d'$ is diameter of the spread laser beam and $l$ is the distance of laser from screen
The problems are
- as the distance $l$ increases, the spread becomes more non-uniform (it spreads more in one direction)
- the the maximum intensity center's diameter ($d$) which also changes with increase in $l$, is not easy to measure as it depends on observer's eyes
Any easier ideas?