Equations · equation
Gaussian Beam Divergence
Photonics · 1966
- Equation
- θ = λ / (π·w₀)
- Field
- Photonics
- Named After
- Herwig Kogelnik · Tingye Li
- Year
- 1966
Symbols
θ far-field half-angle of spread · λ wavelength · w₀ the beam waist, its narrowest radius · diffraction makes tighter focus mean faster spread
Significance
A laser beam cannot stay pencil-thin forever — diffraction spreads it at an angle set by wavelength over waist. The trade is fundamental: focus harder, diverge faster. It's why lunar ranging beams leave Earth centimetres wide and arrive kilometres wide, and still come home with an answer.
Referenced by
constant
element
equation
instrument
Open on the Equations shelf — the interactive card, the filters, and everything alongside it.