# Calculating Laser Beam Intensity Absorbtion

This question pertains to the ability to calculate the laser beam intensity , at a particular point in time when using lasers for the purposes of Cutting and Engraving Materials.

The parameters at play when dealing with this equation so far are:

• Speed the laser is moving at(mm/s)
• Power of the Laser Beam (Watts)
• Diameter / Area of the focussed beam spot (mm)
• Frequency of laser pulse (Hz)
• Duration of laser pulse / rise and fall time of the pulse (ns)

Currently i believe i am able to calculate this laser energy parameter for a Constant Wave laser as follows:

diameter = 1.27 * (focalLength) * Wavelength * ((M^2) / BEAMDIA);
beamArea = 2 * pi * (0.5 * diameter);
beamIntensity = laserAveragePower / (area * speed); // joules/mm^2


However this does not take into account many of the factors i listed above. So my question is: How can i adjust the above formula to include the listed parameters?

For example, how would this be modified to account for a laser being Pulsed at 100Hz, with average power 100W and a 200ns pulse duration.

I am under the impression the Frequency of the laser pulses need to be converted to a unit of measurement, such as "Pulses Per Inch".

Thanks!

• Do you really want the beam energy? Then it shouldn't depend on the spot size. If you want the intensity, then it will depend on the spot size. – The Photon Sep 13 at 16:05
• Yes it is the intensity. I have gotten the terms mixed up it seems. – Brett Sep 13 at 23:15
• Note that intensity is not measured in joules/mm^2. Intensity is a measure of energy flow per unit area, and as such it is measured in watts per square meter (or equivalent units). – Emilio Pisanty Sep 16 at 9:54
• @EmilioPisanty Thanks for pointing this out. Do you also have any idea on how i can modify the equation to incorporate the other factors? – Brett Sep 17 at 10:24
• @Brett No, I don't. I don't really know what it is you're trying to calculate here. – Emilio Pisanty Sep 17 at 15:41