Method __init__

python/source.py:265–336

Construct a `GaussianSource`. + **`frequency` [`number`]** — The center frequency $f$ in units of $c$/distance (or $\\omega$ in units of $2\\pi c$/distance). See [Units](Introduction.md#units-in-meep). No default value. You can instead specify `wavelength=x` or

(
        self,
        frequency=None,
        width=0,
        fwidth=float("inf"),
        start_time=0,
        cutoff=5.0,
        is_integrated=False,
        wavelength=None,
        **kwargs,
    )

    """

    def __init__(
        self,
        frequency=None,
        width=0,
        fwidth=float("inf"),
        start_time=0,
        cutoff=5.0,
        is_integrated=False,
        wavelength=None,
        **kwargs,
    ):
        """
        Construct a `GaussianSource`.

        + **`frequency` [`number`]** — The center frequency $f$ in units of $c$/distance
          (or $\\omega$ in units of $2\\pi c$/distance). See [Units](Introduction.md#units-in-meep).
          No default value. You can instead specify `wavelength=x` or `period=x`, which
          are both a synonym for `frequency=1/x`; i.e. $1/\\omega$ in these units is the vacuum
          wavelength or the temporal period.

        + **`width` [`number`]** — The width $w$ used in the Gaussian. No default value.
          You can instead specify `fwidth=x`, which is a synonym for `width=1/x` (i.e. the
          frequency width is proportional to the inverse of the temporal width).

        + **`start_time` [`number`]** — The starting time for the source; default is 0
          (turn on at $t=0$). This is not the time of the peak. See below.

        + **`cutoff` [`number`]** — How many `width`s the current decays for before it is
          cut off and set to zero — this applies for both turn-on and turn-off of
          the pulse. Default is 5.0. A larger value of `cutoff` will reduce the amount of
          high-frequency components that are introduced by the start/stop of the source,
          but will of course lead to longer simulation times. The peak of the Gaussian is
          reached at the time $t_0$=`start_time + cutoff*width`.

        + **`is_integrated` [`boolean`]** — If `True`, the source is the integral of the
          current (the [dipole moment](https://en.wikipedia.org/wiki/Electric_dipole_moment))
          which is guaranteed to be zero after the current turns off. In practice, there
          is little difference between integrated and non-integrated sources *except* for
          [planewaves extending into PML](Perfectly_Matched_Layer.md#planewave-sources-extending-into-pml).
          Default is `False`.

        + **`fourier_transform(f)`** — Returns the Fourier transform of the current
          evaluated at frequency $f$ ($\\omega=2\\pi f$) given by:
          $$
          \\widetilde G(\\omega) \\equiv \\frac{1}{\\sqrt{2\\pi}}
          \\int e^{i\\omega t}G(t)\\,dt \\equiv
          \\frac{1}{\\Delta f}
          e^{i\\omega t_0 -\\frac{(\\omega-\\omega_0)^2}{2\\Delta f^2}}
          $$
          where $G(t)$ is the current (not the dipole moment). In this formula, $\\Delta f$
          is the `fwidth` of the source, $\\omega_0$ is $2\\pi$ times its `frequency,` and
          $t_0$ is the peak time discussed above. Note that this does not include any
          `amplitude` or `amp_func` factor that you specified for the source.
        """
        if frequency is None and wavelength is None:
            raise ValueError(
                f"Must set either frequency or wavelength in {self.__class__.__name__}."
            )