## 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⋅z_{R} in which the beam waist diameter Ø_{spot} 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

Ø_{spot }= beam waist diameter in µm

### Example

Spot size: Ø_{spot} = 7.1 µm

Wavelength: λ = 780 nm

Rayleigh range: 2z_{R}=20.3 µm