Inversionless terahertz lasing in a four-level Raman-type scheme within mid-infrared quantum cascade structures

This paper applies the density matrix formalism to investigate a feasibility of inversionless terahertz (THz) lasing within a mid-infrared (mid-IR) quantum cascade laser (QCL). The proposed structure aims to use a mid-IR QCL as an efficient pump source that integrated with a four-level Raman-type scheme to generate THz radiation through strong coherence excited in the system. A key aspect of the design is that the THz generation is achieved by interplay between inversion-based lasing and coherent effects due to quantum interference between the microscopic polarizations of the dipole-allowed transitions in the four-level system. THz intensity gain arising from both the inversion-based lasing and coherent effects is derived from the off-diagonal density matrix elements in the four-level system. The simulation results indicate that the proposed design demonstrates the potential to achieve THz lasing with good temperature characteristics and without the need for population inversion.

Automated summary

This paper investigates the feasibility of inversionless terahertz (THz) lasing in a mid-infrared (mid-IR) quantum cascade laser (QCL) using the density matrix formalism. The proposed structure integrates a mid-IR QCL as a pump source with a four-level Raman-type scheme to generate THz radiation through strong coherence excited in the system. The interplay between inversion-based lasing and coherent effects in the four-level system leads to THz intensity gain derived from the off-diagonal density matrix elements.