Terahertz Waveforms Generated by Second-Order Nonlinear Polarization in GaAs/AlAs Coupled Multilayer Cavities Using Ultrashort Laser Pulses

Temporal terahertz waveforms generated from GaAs/AlAs coupled multilayer cavity structures were simulated and compared with experimental results. Femtosecond laser pulses covering two cavity-mode frequencies were used for the difference frequency generation (DFG) in the terahertz region. The Fourier components dependent on the frequency and spatial position were determined for the second-order nonlinear polarization induced by a 100-fs Gaussian pulse injection. When the temporal waveform was simulated using the Fourier components, the oscillating behavior due to the efficient DFG of the two cavity modes was clearly observed after the initial ultrafast response near the incident surface. Assuming the exponential decay of signal sensitivity in the high-frequency region, the simulated results were consistent with the experimentally measured ones for coupled cavity structures grown on (113) B GaAs substrates.