finesse.detectors.knmdetector.KnmDetector

Overview

class finesse.detectors.knmdetector.KnmDetector(name, comp, coupling, n1=None, m1=None, n2=None, m2=None)

Bases: Detector

Direct probe of coupling coefficients at a component.

This detector has several “modes” which depend upon the values given for the mode indices n1, m1 and n2, m2. If:

• all of n1, m1, n2, m2 are specified then the detector will output a single complex coefficient corresponding to the coupling from (n1, m1) -> (n2, m2),

• just n1 and m1 are specified then it will output a vector of complex coefficients corresponding to each coupling from (n1, m1) -> (n, m) for each mode (n, m) in the model,

• only n2 and m2 are specified then it will output a vector of complex coefficients corresponding to each coupling from (n, m) -> (n2, m2) for each mode (n, m) in the model,

• none of n1, m1, n2, m2 are specified then the detector outputs the full matrix of complex coupling coefficients.

Hint

When using this detector in “full-matrix” mode (i.e. by not giving the values for any of the mode indices), it can be useful to combine the output with the KnmMatrix object to obtain a more convenient representation of the scattering matrix.

An example of this is shown below, where the output of a detector of this type is wrapped using KnmMatrix.from_buffer().

import finesse
finesse.configure(plotting=True)
from finesse.knm.matrix import KnmMatrix

IFO = finesse.Model()
IFO.parse('''
l L0 P=1
link(L0, ITM)
m ITM R=0.99 T=0.01 Rc=-2090 xbeta=0.3u
s LARM ITM.p2 ETM.p1 L=4k
m ETM R=0.99 T=0.01 Rc=2090

cav ARM ITM.p2
modes(x, maxtem=6)

knmd K_itm_r ITM 22
''')

out = IFO.run()
# Make a KnmMatrix wrapper around the output from the detector
k_mat = KnmMatrix.from_buffer(out["K_itm_r"], IFO.homs)
# Now we can perform operations such as plotting the scattering matrix
k_mat.plot(cmap="bone");

See Computing arbitrary scattering matrices for some examples on the utility that the KnmMatrix object provides.

Parameters:

namestr

Name of newly created KnmDetector.

compConnector

A component which can scatter modes.

couplingstr

Coupling direction string, e.g. “11” for coupling coefficients on reflection from the front surface of a mirror.

n1, m1, n2, m2: int or None

From (n1, m1) and To (n2, m2) mode indices of the coupling coefficient(s) to retrieve.

See above for the options.