How do I calculate the fluence of a Gaussian Laser Beam?

[Kanneman5413]

Summary: Need to calculate the fluence of Gaussian Laser Beam: laser tip 1 cm above surface, tilted at 45 0 angle to surface.

Need to calculate the fluence of Gaussian Laser Beam: laser tip 1 cm above surface, tilted at 45 0 angle to surface.

Laser tip size 1 mm across
Diameter 0.5 mm

Surface area = pi r 2
3.14 x (0.5)2
0.79 mm 2
= 0.0079 cm 2

Beam diverts 6 degrees both sides of tip
tan 6 0 = 0.11 cm (base of triangle)

Triangle surface = 1/2 x base x height
= 0.055 cm 2

Total surface = (0.055 cm 2 x 2 ) + 0.0079 cm 2
= 0.1179 cm 2
45 0 angle: cosin 45 0 = 0.707

Total surface 0.1179 cm² ÷ cos 45°
= 0.17 cm²

Pulse Energy = P(average) ÷ Pulse Frequency
= 0.5 W ÷ 30 Hz
= 0.01667 J

Fluence = Energy of laser pulse / Area of spot
= 0.01667 J / 0.17 cm 2
= 0.0980 J/cm² ( area is irradiated for 30 seconds)

( do I multiply ?? x 30 s)
= 2.94 J/cm² (??)

Fluence = (average power) / rep rate/ spot area
= 30 Hz / 0.17cm^2 x 0.5 W
=88.24 J/cm^2 ( ??)

Please help!

 

[mfb]

A sketch would help.

This is not high energy physics. As it looks like a homework problem I moved it there.

 

[Kanneman5413]

Trust you can open the sketch

 

[mfb]

Thanks.

I don't understand the area calculation (at 90 degrees). Shouldn't it be a circular spot with a diameter of 1mm + 2*1.1mm?

There is a higher order effect from the combination of the 6 degree divergence and the 45 degree angle that increases the area, but that is probably small.

All Js should be J/s.