# Rayleigh range

## Rayleigh range

### Determination of the Rayleigh range

Beam path of focused beam.

For a Gaussian beam the depth of focus is defined by the ­Rayleigh range 2⋅zR in which the beam waist diameter Øspot does not ­increase more than a factor of 1.41.

{!{!{2z_R=\frac{2\cdot\pi\cdot\emptyset_{spot}^2}{4\lambda}}!}!}
λ = wavelength in µm
Øspot = beam waist diameter in µm

### Example

Spot size: Øspot = 7.1 µm

Wavelength: λ = 780 nm

Rayleigh range: 2zR=20.3 µm