focusaniso

A small tool to simulate focusing in anisotropic media

Installation

You can simply put the file focusaniso.py where you want it. The only dependency is numpy.

Alternatively, you can install the module with pip install git+https://git.scc.kit.edu/photonics/focusaniso.git. I'd advise to do this in a virtual environment. For the documentation and tests use pip install -e git+https://git.scc.kit.edu/photonics/focusaniso.git#egg=focusaniso[docs,test]. Omit docs or test, if you only want one of them.

Getting started

We want to do a small example based on the results of S. Wang et al. For more examples see the examples folder. First, we import the module and define the properties.

import numpy as np
import focusaniso as fa

k0 = 2 * np.pi # Wavelength is one
f = 60 # Focus length equal to 60 wavelengths
na = 1.4 # Numerical aperture
n2 = 1.518 # Refractive index of the medium focused into

# Those parameters mainly influence the accuracy
nrho = 23 # Radial values
nphi = 72 # Azimuthal values
# The beam is shaped as a ring with constant power between 0.9 * NA and NA with
# circular polarization
rhos, phis = np.meshgrid(
    f * na / n2 * np.linspace(0.9, 1, nrho)),
    np.linspace(0, 2 * np.pi * (1 - 1 / nphi), nphi),
)
beam = np.ones_like(rhos)[:, :, :] * np.array([1, 1j, 0]) * np.sqrt(0.5)

Next, we define that this beam is a real space spectrum defined on a polar grid and then immediatly focus that light.

spec = fa.Spectrum(beam, rhos, phis, k0, coord='polar')
spec.focus(f, n2=n2)

Now we turn to the materials, where we have the immersion oil where we focused into, and a uniaxial crystal with the interface 30 wavelengths in front of the focus.

oil = Material(n2**2)
crystal = Material(np.diag([1.6555**2, 1.6555**2, 1.4851**2]))
stack = Stack([-30, -30], [oil, crystal])

We will propagate the focused spectrum in this stack and probe it at a several z values

z_probe = np.linspace(-10, 15, 251)
specs_probe = spec.field(stack, zs)

These angular spectra will be converted to the real space at multiple x values, such that the electric field is known in a x-z-plane.

x_probe = np.linspace(-2, 2, 41)
abs_sq_efield = np.zeros((41, 241))
for i, s in enumerate(specs_probe):
    s.setspace('real', x_probe, 0)
    abs_sq_efield[:, i] = np.sum(np.power(np.abs(s.grid), 2), axis=-1)

Documentation

The documentation is created with sphinx. Run make html in the docs directory. Then, html files are found in docs/_build/html/ with index.html being the starting page. You can also create a pdf file using latex with make latexpdf in the docs directory, which is put in docs/_build/latex/focusaniso.pdf

Testing

The tests are done with pytest, using python -m pytest. Use the option --cov focusaniso for a coverage report.