tidy3d.TwoPhotonAbsorption#

class TwoPhotonAbsorption[source]#

Bases: NonlinearModel

Model for two-photon absorption (TPA) nonlinearity which gives an intensity-dependent absorption of the form $\alpha ={\alpha }_0+\beta I$. The expression for the nonlinear polarization is given below.

Parameters:

• beta (Attribute: beta) –

  Type	Union[tidycomplex, ComplexNumber]
  Default	= 0
  Units	um / W
  Description	Coefficient for two-photon absorption (TPA).

• n0 (Attribute: n0) –

  Type	Union[tidycomplex, ComplexNumber, NoneType]
  Default	= None
  Description	Complex linear refractive index of the medium, computed for instance using ‘medium.nk_model’. If not provided, it is calculated automatically using the central frequencies of the simulation sources (as long as these are all equal).

Note

$$P_{NL}=-\frac{c_0^2{\epsilon }_0^2{n}_0\mathrm{Re}(n_0)\beta }{2i\omega }|E{|}^{2}E$$

Note

This frequency-domain equation is implemented in the time domain using complex-valued fields.

Note

Different field components do not interact nonlinearly. For example, when calculating $P_{NL,x}$, we approximate $|E{|}^2\approx |E_x{|}^2$. This approximation is valid when the E field is predominantly polarized along one of the x, y, or z axes.

Note

The implementation is described in:

N. Suzuki, "FDTD Analysis of Two-Photon Absorption and Free-Carrier Absorption in Si
High-Index-Contrast Waveguides," J. Light. Technol. 25, 9 (2007).

Example

>>> tpa_model = TwoPhotonAbsorption(beta=1)

Attributes

complex_fields

Whether the model uses complex fields.

Methods

beta#

n0#

property complex_fields#

Whether the model uses complex fields.

__hash__()#

Hash method.