finesse.knm.maps.scattering_coefficients_to_KnmMatrix

finesse.knm.maps.scattering_coefficients_to_KnmMatrix(modes, K)

Converts a 4-D scattering coefficient array into a 2D KnmMatrix object to be used in simulations.

Parameters

modestuple, array

Array of 2D modes indicies (n,m) to specify the order in which they appear in the returned matrix.

Karray

4D array of coefficients indexed with [in_x, out_x, in_y, out_y]

Returns

KnmKnmMatrix

A KnmMatrix class representing a 2D scattering matrix for the requested modes.

Examples

Compute KNM matrix from a previously calculated 4-D scattering coefficient array:

import finesse
from finesse.knm.maps import (
    map_scattering_coefficients,
    scattering_coefficients_to_KnmMatrix
)
import numpy as np

# compute all scatterings up to maximum TEM order
maxtem = 3
q = finesse.BeamParam(w0=1e-3, z=0)
x = np.linspace(-4*q.w, 4*q.w, 201)
y = np.linspace(-4*q.w, 4*q.w, 200)
X, Y = np.meshgrid(x, y)
# Mix of liner and quadratic phase terms to compute scattering
# coefficients for
Z = np.exp(1j * 1e-6 * 2 * np.pi * X / 1064e-9)
K = map_scattering_coefficients(q, maxtem, x, y, Z)
# Generate specific ordering of coefficients into a 2D matrix that can
# be used in simulations for propagating and array of modes.
modes = (
    (0,0),
    (1,0),
    (2,1),
)
Knm = scattering_coefficients_to_KnmMatrix(modes, K)
# Propagate some mode amplitudes
Knm.data @ [1, 0.1, 0]
>>> array([9.99995641e-01+2.95261180e-04j,
           9.99986923e-02+2.95261180e-03j,
           4.23516474e-22+2.16840434e-20j])