In the world of laser material interactions, we talk very often "laser fluence", which is the division of laser power (pulse energy at a given repetition rate) over the surface area.
The power is to do with solid numbers that one can measure with a power meter. The surface area is, though, less obvious in that aspect, a part from classic gaussian beam enenrgy distribution, one cannot easily define a "surface area " for the aforementioned fluence to be calculated.
Concerning donut-shaped beams, with a typical example being s-waveplate induced radial/azimithal polarized laser beam, how could one evaluate the beam area?
thanks in advance for your valuable comments!
For any kind of beam shape (including distorted ones) the best approach I think is "power in the bucket." From the intensity distribution you derive the centroid (the "point of gravity"), and you draw a circle around that. Increase the diameter until a predetermined total amount of power (e.g. 90%) is contained within the circle. This can be used as a measure of "spot size"
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