If fluence is constant over the laser spot, Its very simple, you must multipy fluence and spot size. But if you know only fluence in the maximum of laser spot, you must 1) measure the transverse distribution of fluence with a beam profiler and then 2) integrate spatial diatribution to energy of the whole beam
Well if you know the symmetry of the beam you can also estimate E from fluence.
E.g. for Gaussian beams is just E=F/2*SpotArea
while for Top-Hat results
E=F*SpotArea
if you have something in between then you have a bit more complex Eq (also depending on whether your beam is truncated or not).
where I0 is the peak radiant exposure (at the axis of the laser beam), R0 is the beam size when the radiant exposure falls to 1/e2 its peak value, N is the super-gaussian order of the beam profile (where N=1 represents a pure Gaussian beam profile, and N=∞ represents a flat-top beam profile), PH is the pinhole diameter (the truncation diameter), EPulse is total energy of the laser pulse and lowercase gamma is the lower incomplete gamma function (the incomplete limits version of the general factorial function for non-integer arguments).
Dear Aleksandr and Samuel
Thank you very much for your guidance
Regards
M G B Ashiq
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