Sources¶

All the photon packet sources that can be used in the Monte Carlo simulator are implemented by subclassing xopto.mccyl.mcsource.base.Source. The xopto.mccyl.mcsource module includes a number of commonly used sources:

xopto.mccyl.mcsource.point.IsotropicPoint implements an isotropic point source.
xopto.mccyl.mcsource.line.Line implements an infinitely narrow and collimated source.
xopto.mccyl.mcsource.uniformbeam.UniformBeam implements a uniform collimated source of elliptical cross section.
xopto.mccyl.mcsource.gaussianbeam.GaussianBeam implements a collimated Gaussian source of elliptical cross section.

All sources have a position attribute that defines the position of the geometrical center of the source. This position is used as a reference point for terminating photon packets that leave the simulation radius set through the xopto.mccyl.mc.Mc.rmax property. Note that by default all the sources point along the positive direction of the $x$ axis and enter the outer layer of the sample on the negative $x$ axis at $x=d/2$ .

Note

The refractive index of the source (not all the sources implement this property) is used to compute the initial photon packet weight (the specular reflectance at the source-sample boundary is subtracted from 1.0). The sources that do not implement a refractive index, inherit the value from the surrounding medium.

The UniformBeam, xopto.mccyl.mcsource.gaussianbeam.GaussianBeam and all the fiber sources

Isotropic point¶

This source can be placed inside and outside the sample. The following example shows how to create an isotropic point source in the center of the sample:

from xopto.mccyl import mc

src = mc.mcsource.IsotropicPoint((0.0, 0.0, 0.0e-3))

If the source is positioned outside of the sample, the entry point into the sample is determined by propagating the packet from the source position along the launch direction. The MC simulation will start after refracting the packet into the sample and subtracting the specular reflectance at the sample boundary from the initial weight of the packet. If the photon packet does not intersect the sample, the initial weight will be set to 0 and the packet will be launched from the center of the sample $(x,y,z)=(0, 0, 0)$ . Such zero-weight packets are immediately terminated and have no contribution to the fluence and surface detector, however will be included in the trace (have no effect on the sampling volume or other trace-based analysis due to the zero-weight). Note that in case the position lies within the sample, it will be used as the launch point and the packets will retain the full initial weight.

Line¶

The following example shows how to create a Line source that enters the sample 1 mm of the $x$ axis and propagates in the direction of the $x$ axis:

from xopto.mccyl import mc
import numpy as np

ang = np.deg2rad(10.0)
src = mc.mcsource.Line(position=(0.0, 1.0e-3, 0.0), direction=(1.0, 0.0, 0.0))

The packets are always launched from the outer surface of the sample. The source position and direction are used to determine the launch point at the sample surface. From there, the packet is first refracted into the sample and the surface reflectance is subtracted from the initial packet weight. If a specular surface detector is used, the reflectance is deposited into that detector.

Uniform beam¶

A uniform beam of elliptical cross section can be created with xopto.mccyl.mcsource.uniformbeam.UniformBeam source. The beam diameter along the y and z axis is controlled by the diameter parameter. In case the diameter is give as a scalar float value, the cross section of the beam becomes circular. Note that the diameters are applied in the coordinate system of the beam. Optionally, the beam can be repositioned and tilted through the position and direction parameters. The following example creates a uniform beam with incidence along the $axis$ and a circular cross section diameter of 1 mm.

from xopto.mccyl import mc

src = mc.mcsource.UniformBeam(1.0e-3)

The packets are always launched from the top surface of the sample. The source position and direction are used to determine the launch point at the sample surface. From there, the packet is first refracted into the sample and the surface reflectance is subtracted from the initial packet weight. If a specular surface detector is used, the reflectance is deposited into that detector.

Gaussian beam¶

A Gaussian beam can be created with xopto.mccyl.mcsource.gaussianbeam.GaussianBeam source. The standard deviation ( $\sigma$ ) of the beam can be independently set along the x and y axis. In case $\sigma$ is give as a scalar float value, the value is applied along the y and z axis. The beam is clipped at a distance of $5\sigma$ from the beam axis. The clip distance can be customized through the clip parameter. Note that $\sigma$ is applied in the coordinate system of the beam. Optionally, the beam can be repositioned and tilted through the position and direction parameters. The following example creates a GaussianBeam source with a perpendicular incidence and with $\sigma_y$ 1 mm and $\sigma_z$ 2 mm.

from xopto.mccyl import mc

src = mc.mcsource.GaussianBeam([1.0e-3, 2.0e-3])

The packets are always launched from the surface of the sample. The source position and direction are used to determine the launch point at the sample surface. From there, the packet is first refracted into the sample and the reflectance is subtracted from the initial packet weight. If a specular surface detector is used, the reflectance is deposited into that detector.