Time domain analysis of a superconductor's nonlinear THz response

We analyze the response of a BCS-type superconductor exposed to a strong THz pulse using the FDTD method in combination with a model time-dependent susceptibility having an explicit dependence on the superconductor's energy gap Δ. In the analysis, the energy gap is allowed to be time varying through its dependence on the current density, along with a relaxation time related to the inelastic electronic scattering rate. The model accounts for 3rd harmonic generation effects and can be applied to the case of an incident, strong-field, single or few cycle pulse for which significant nonlinear effects can occur.