import numpy as np
from finesse.detectors.general import Detector
from finesse.detectors.compute.gaussian import BPDetectorWorkspace, BeamProperty
# Map of beam property keywords to enum fields.
BP_KEYWORDS = {
"w": BeamProperty.SIZE,
"w0": BeamProperty.WAISTSIZE,
"z": BeamProperty.DISTANCE,
"zr": BeamProperty.RAYLEIGH,
"gouy": BeamProperty.GOUY,
"div": BeamProperty.DIVERGENCE,
"rc": BeamProperty.ROC,
"s": BeamProperty.DEFOCUS,
"q": BeamProperty.Q,
}
[docs]class BeamPropertyDetector(Detector):
r"""Probe for detecting the properties of a beam at a given node.
The valid values for `prop` are:
* ``"w"``: beam size at `node` [metres],
* ``"w0"``: waist size as measured at `node` [metres],
* ``"z"``: distance to the waist from `node` [metres],
* ``"zr"``: the Rayleigh range [metres],
* ``"gouy"``: the Gouy phase of the beam at `node` [radians],
* ``"div"``: divergence angle of the beam at `node` [radians],
* ``"rc"``: radius of curvature of wavefront at `node` [metres],
* ``"s"``: curvature of wavefront at `node` [1 / metres],
* ``"q"``: beam parameter at `node`.
.. note::
The ``"gouy"`` target property here detects the Gouy phase as derived
from the beam parameter :math:`q` at the specified node, i.e:
.. math::
\psi = \arctan{\left(\frac{\myRe{q}}{\myIm{q}}\right)}.
It does **not** compute any Gouy phase accumulation. Use :class:`.Gouy`
to detect the accumulated Gouy phase over a path.
Parameters
----------
name : str
Name of newly created detector.
node : :class:`.OpticalNode`
Node to read output from.
prop : str or :class:`.BeamProperty`
The property of the beam to detect. See above for options.
direction : str, optional; default: 'x'
Plane to detect in - 'x' for tangential, 'y' for sagittal.
q_as_bp : bool, optional; default: False
If detecting q, should the detector output return :class:`.BeamParam`
object instead of just a complex number.
"""
def __init__(self, name, node, prop, direction="x", q_as_bp=False):
if isinstance(prop, str):
if prop.casefold() not in BP_KEYWORDS:
raise ValueError(
f"Unrecognised property: {prop}, expected "
f"one of: {list(BP_KEYWORDS.keys())}"
)
prop = BP_KEYWORDS[prop.casefold()]
if prop == BeamProperty.Q:
if q_as_bp:
dtype = object
else:
dtype = np.complex128
units = ""
else:
dtype = np.float64
if prop == BeamProperty.GOUY or prop == BeamProperty.DIVERGENCE:
units = "radians"
elif prop == BeamProperty.DEFOCUS:
units = "1/m"
else:
units = "m"
property_to_label = {
BeamProperty.SIZE: "Beam size",
BeamProperty.WAISTSIZE: "Beam waist-size",
BeamProperty.DISTANCE: "Distance to beam waist",
BeamProperty.RAYLEIGH: "Rayleigh range",
BeamProperty.GOUY: "Gouy phase",
BeamProperty.DIVERGENCE: "Divergence angle",
BeamProperty.ROC: "Beam radius of curvature",
BeamProperty.DEFOCUS: "Beam defocus",
BeamProperty.Q: "Beam parameter",
}
label = property_to_label[prop]
Detector.__init__(self, name, node, dtype=dtype, unit=units, label=label)
self.__prop = prop
self.direction = direction
self.q_as_bp = q_as_bp
@property
def prop(self):
return self.__prop
@property
def needs_fields(self):
return False
@property
def needs_trace(self):
return True
@property
def detecting(self):
"""The property of the beam which is being detected.
:getter: Returns the detected property (read-only).
"""
return self.__prop
def _get_workspace(self, sim):
ws = BPDetectorWorkspace(self, sim)
ws.q_as_bp = self.q_as_bp
return ws