In optics, the complex beam parameter is a complex number that specifies the properties of a Gaussian beam at a particular point z along the axis of the beam. It is usually denoted by q. It can be calculated from the beam's vacuum wavelength λ0, the radius of curvature R of the phase front, the index of refraction n (n=1 for air), and the beam radius w (defined at 1/e2 intensity), according to:
- .
Alternatively, q can be calculated according to
where z is the location at which q is calculated, relative to the location of the beam waist, z0 is the Rayleigh range, and i is the imaginary unit.
Read more about Complex Beam Parameter: Uses of The Complex Beam Parameter
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—Henry Abbey (1842–1911)