摘要
A broadly tunable THz source is realized via difference frequency generation,in which an enhancement to χ^((3)) that is obtained via resonant excitation of III–V semiconductor quantum well excitons is utilized.The symmetry of the quantum wells(QWs)is broken by utilizing the built-in electric-field across a p-i-n junction to produce effectiveχ(2)processes,which are derived from the high χ^((3)).This χ^((2)) media exhibits an onset of nonlinear processes at~4Wcm−2,thereby enabling area(and,hence,power)scaling of the THz emitter.Phase matching is realized laterally through normal incidence excitation.Using two collimated 130mW continuous wave(CW)semiconductor lasers with ~1-mm beam diameters,we realize monochromatic THz emission that is tunable from 0.75 to 3 THz and demonstrate the possibility that this may span 0.2-6 THz with linewidths of ~20 GHz and efficiencies of ~1×10^(-5),thereby realizing ~800 nW of THz power.Then,transmission spectroscopy of atmospheric features is demonstrated,thereby opening the way for compact,low-cost,swept-wavelength THz spectroscopy.
