TwoPhotonAbsorption

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.

$P_{NL} = -\frac{c_{0}^{2} \varepsilon_{0}^{2} n_0 Re(n_0) \beta}{2 i \omega} |E|^{2} E$

Coefficient

beta: Coefficient for two-photon absorption (TPA). You can include complex values using the real and imaginary edit boxes.

Type: complex number

• Unit: μm/W
• Default: 0

Notes

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