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Source

from ikarus import Source

The plane wave doing the illuminating. Usually you create it indirectly through RCWA.set_source — but it's a plain dataclass you can build and inspect directly.

Source

Source(wavelength, theta=0.0, phi=0.0,
       polarization="linear", linear_pol_angle=0.0, n_incident=1.0)

Parameters

Name Type Default Description
wavelength float — Vacuum wavelength (m); must be positive.
theta float 0.0 Polar angle from +z (deg). 0 = normal incidence.
phi float 0.0 Azimuth from +x in the xy-plane (deg).
polarization str "linear" One of "linear", "RCP", "LCP".
linear_pol_angle float 0.0 For linear: angle from TE (deg). 0 = TE/s, 90 = TM/p.
n_incident complex 1.0 Index of the cover medium; set automatically by the solver from the top layer.

Raises. ValueError for an unknown polarization or non-positive wavelength.

Angle and polarization conventions

theta is measured from +z (the wave travels in -z, into the stack). The transverse basis is \(\hat a_{TE} = \hat z \times \hat k\), \(\hat a_{TM} = \hat a_{TE} \times \hat k\). At normal incidence the split is degenerate, so Ikarus pins \(\hat a_{TE} = +\hat y\), \(\hat a_{TM} = +\hat x\) — linear_pol_angle becomes the literal E-field angle in the xy-plane. Theory → Polarization has the full picture.

Properties

Property Description
k0 Vacuum wavenumber \(2\pi/\lambda\) (rad/m).
theta_rad, phi_rad The angles in radians.

Methods

incident_wavevector() -> ndarray

Normalized (by k0) incident wavevector \((k_x, k_y, k_z)\) in the cover medium.

kx0_ky0() -> (complex, complex)

The in-plane components \((k_{x0}, k_{y0})\) — continuous across all layers.

polarization_vector() -> ndarray

Complex unit polarization vector \((p_x, p_y, p_z)\), transverse to \(k\).

te_tm_vectors() -> (ndarray, ndarray)

The real TE and TM unit vectors for the current geometry.

copy_with(**changes) -> Source

A copy with selected fields overridden — the mechanism behind the stateful set_source used in sweeps.

Examples

from ikarus import Source

# TM (p-polarized) wave at 30 degrees, 1550 nm.
src = Source(wavelength=1550e-9, theta=30, polarization="linear", linear_pol_angle=90)
print("k0 =", src.k0)
print("polarization vector =", src.polarization_vector())

# Right-circular at normal incidence.
rcp = Source(wavelength=633e-9, polarization="RCP")

# Derive a tweaked copy without mutating the original.
src_15 = src.copy_with(theta=15)

Best practices

  • Prefer RCWA.set_source(**kwargs) over constructing Source directly — it wires n_incident from the cover layer for you.
  • Phase work across tools: Ikarus reports phase in the physics \(\exp(-i\omega t)\) convention; another code may differ by a sign or constant offset (FAQ #13).