Resonant crossover of terahertz loss to gain in a Bloch oscillating InAs/AlSb super-superlattice

Summary form only given. Terahertz absorption in waveguides loaded with InAs/AlSb super-superlattice mesas reveals a frequency dependent cross over from loss to gain that is related to the Stark ladder produced by an applied DC electric field. Resonant crossover is indicated by an increase in terahertz transmission as the Stark splitting or Bloch frequency determined by the applied DC electric field exceeds the measurement frequency. The measurements are carried out at room temperature. Super-superlattice mesas are loaded into a terahertz waveguide, 10 μm high and ∼300 μm wide, defined by photonic band gap side walls and metallic ceiling and floor. Terahertz radiation (1.5-2.6 THz) from the UCSB free-electron lasers is focused on the entrance and guided to a detector. Electric field domains appear to be suppressed in the super-superlattice comprised of many very short segments of superlattice, interrupted by heavily doped InAs regions. Scaling of the crossover voltage by the terahertz frequency indicates that ∼75% of the super-superlattice participates in the Stark ladder. These results indicate that super-superlattices in terahertz waveguides as described here can provide a terahertz gain medium without population inversion and a resonator for a terahertz Bloch oscillator.