Physics

Laser Beam Spot Size Calculator

Find a laser beam's diameter at a distance.

Initial beam diameter

Divergence (full angle) (mrad)

Distance

Calculated Output

Spot diameter 102

Formula: spot = initial + distance × divergence

Step-by-Step Breakdown

1. Values used:

2. Initial beam diameter = 2

3. Divergence (full angle) = 1 mrad

4. Distance = 100

6. Spot diameter = 102

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The math behind it

Far-field spot diameter ≈ initial diameter + distance × full-angle divergence (in radians).

2 mm beam, 1 mrad, 100 m → about 102 mm.

How to keep a small spot far away?

Lower the divergence with a beam expander.