# Sources

TEMPORARILY, USE THE FOLLOWING BELOW TO DEFINE SOURCES -- THIS MESSAGE CONTAINS A CLOSING BLOCK BELOW

Currently, the source in FDTD++, is generally-defined so as to provide accurate Fourier-transformed fields over some specified frequency range. Specifically, the source is defined as the product of a $\sin$ function (a plane wave), setting a center frequency, and a Gaussian function that gives the source a frequency width: $$\textbf{E}^\text{inc} = \mathbf{\hat{u}} ~ \text{E}_0 \sin ( \omega t ) ~ e^{-\frac{(t - t_0)^2}{2 \sigma^2}}$$ where $\mathbf{\hat{u}}$ is a unit-vector pointing in the polarization direction of the field, $\text{E}_0$ is the incident amplitude (currently assumed to always be 1), $\omega$ is the center frequency, $t_0$ is the center of the Gaussian function, and $\sigma$ is its standard deviation.

## Source parameters

The following simulation parameters define the incident field, as discussed above:

• src_pol str: Sets the polarization vector ($\mathbf{\hat{u}}$) of the incident field to str. Valid values of str are x ($x$-polarization), y ($y$-polarization), 45 (45 degree polarization), or circ (circular polarization). The default value of str is x.
• src_sin_wave #: Sets the wavelength ($\frac{2 \pi}{\omega} c$) of the $\sin$ function to #. The default value of # is 545e-9 m (545 nm).
• src_Gauss_center #: Sets the center (time) of the Gaussian function $t_0$ to #. The default value of # is 10.0e-15 s (10 fs).
• src_Gauss_width #: Sets the standard deviation of the Gaussian function ($\sigma$) to #. The default value of # is 0.4e-15 (0.4 fs).

#### Total-field/scattered-field (TF/SF)

• TFSF_z #: Set the $z$-position of the TF/SF plane to #. The default value is 20.0e-9 (20 nm).

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