finesse.knm.maps.Map.get_quadratic_terms

Map.get_quadratic_terms(self, double spot_size: float)

Returns the spot weighted x and y quadratic terms from the OPD map data. For a surface z this is:

\[z(x,y) = a x^2 + b y^2 \]

It’s common to want to get an equivalent curvature or thin-lens focal length for a map. The quadratic component can be related to the curvature on reflection as

\[a = \frac{1}{2 R} \]

or a single pass of a thin lens

\[a = -\frac{1}{2 f} \]

Parameters:

spot_sizefloat

Spot size to use for weighting during curvature removal

Returns:

a, b(float, float)

Quadratic terms in x and y