Fundamental studies on semiconductor coupled multilayer cavity for novel planar-type terahertz emission devices

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Difference-frequency generation (DFG) of two cavity modes in a semiconductor coupled multilayer cavity is a new concept for compact and useful planar-type terahertz emission devices. In this study, we developed fundamental technologies for design and fabrication of the coupled multilayer cavity based on GaAs/AlAs multilayer structures and demonstrated its usefulness as a terahertz light source by measuring various types of frequency-mixing signals using femtosecond laser pulses. We found that the nonlinear susceptibility inversion inside the coupled cavity structure is one of the most important technologies for strong DFG in the terahertz region. The susceptibility inversion was successfully introduced by direct wafer-bonding of two epitaxial films grown on high-index substrates. Signal enhancement due to the inversion was clearly observed in both simulated and experimentally measured terahertz waveforms using femtosecond laser pulses.