Terahertz lasers based on optically pumped four-level asymmetrical double quantum wells

► A prototype of terahertz laser based on four-level asymmetric double quantum well (QW) structures is presented. ► The prominent feature of this prototype is its close proximity of subband 0 and 1. ► An ensemble Monte Carlo method is adopted to comparatively analyze the electron population on each subband. ► We find this design can greatly improve the optically pumping efficiency. ► We propose to use the electric field Stark effect in QW to obtain the close proximity of subband 0 and 1 in double QW.