Abstract
This paper aims to integrate AlInAs/InGaAs quantum well structures with high second-order nonlinear susceptibility into a dual-wavelength quantum cascade laser (QCL) for difference frequency generation (DFG) of THz radiation. The QCL active region contains two sections: a section with 30 cascades of bound-to-continuum design with integrated optical nonlinearity emitting at 8.7 mum and a section with 20 cascades of two-phonon design emitting at 7.6 mum. The nonlinear susceptibility for the DFG process is found to have a value of chi(2)~4times105 pm/V.
Highlights
The Harvard community has made this article openly available
We demonstrate a monolithically integrated device designed to combine the advantages of electrically pumped semiconductor lasers and nonlinear optical sources
Our device is a dualwavelength quantum cascade laser[8] with the active region engineered to possess giant second-order nonlinear susceptibility associated with intersubband transitions in coupled quantum wells
Summary
Mikhail A., Federico Capasso, Alexey Belyanin, Deborah L. An alternative way to produce terahertz radiation is frequency down-conversion in a nonlinear optical crystal using infrared or visible pump lasers[5,6,7]. For intracavity DFG in dual-wavelength semiconductor lasers, the intensities of the pump beams are limited to 1 –10 MW cm[22], and the coherence length is limited to hundreds of micrometres by free-carrier absorption at THz frequencies. High optical nonlinearity in these structures is achieved because all interacting fields are in resonance with intersubband transitions This results in strong absorption of the pump and THz-DFG beams and unavoidably limits THz-DFG efficiency.
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