Thermoelectrically cooled THz quantum cascade laser operating up to 210 K

Abstract: We present a \MF{terahertz} quantum cascade laser operating on a thermoelectric cooler up to a record-high temperature of 210.5 K. The active region design is based on only two quantum wells and achieves high temperature operation thanks to a systematic optimization by means of a nonequilibrium Green's function model. Laser spectra were measured with a room temperature detector, making the whole setup cryogenic free. At low temperatures ($\sim 40 K), a maximum output power of 200 mW was measured.

Thermoelectrically Cooled THz Quantum Cascade Laser Operating up to 210 K

This paper presents a notable advancement in the operation of terahertz (THz) quantum cascade lasers (QCLs) by demonstrating a device that operates at temperatures up to 210 K using a thermoelectric cooler. Utilizing a two-well design optimized through nonequilibrium Green's function (NEGF) modeling, the study provides insights into the structural parameters that enhance the thermal performance of THz QCLs.

Highlights of the Research

1. Design Optimization: The laser achieves high-temperature functionality through an innovative optimization of its two-well active region design. This approach focuses on maximizing gain relative to the population of the upper laser state (ULS), effectively reducing intersubband re-absorption and increasing population inversion.

2. Temperature Performance: Operating at temperatures beyond 200 K is particularly significant as it shifts away from reliance on cryogenic cooling systems. The study achieves this by leveraging NEGF modeling to optimize the laser design for higher stability and efficiency.

3. Integration with Thermoelectric Cooling: The integration of a commercial DTGS detector and a four-stage Peltier cooler in the setup results in a cryogenic-free platform for THz QCL, highlighting a potential transition towards more compact and accessible THz spectroscopy systems.

4. Experimental Validation: The devices were systematically tested, and the NEGF model predictions successfully matched experimental results concerning current and frequency. The maximum output power, measured at low temperatures, reached 200 mW.

Implications and Future Directions

This advancement has substantial implications for the practical deployment of THz QCLs. By achieving operational temperatures using thermoelectric cooling, the pathway for portable and on-chip THz devices becomes feasible. This development provides a promising outlook for wide adoption in sectors such as security imaging and non-destructive testing.

The paper also sets a foundation for future research aimed at further enhancing both temperature resilience and optical power output of THz QCLs. Key areas for continued investigation include the refinement of QCL designs, barrier height adjustments, precise doping strategies, and improving waveguide fabrication processes.

Through these improvements, the maximum operating temperature and power efficiency can potentially be increased, leading to more robust THz technology applications. Overall, the results propound a significant evolution in THz laser design and application, indicating further exploration could yield devices capable of functioning efficiently at a room-temperature range.

Given these findings, the advancements presented in the paper should stimulate ongoing research efforts in THz QCL optimization, encouraging interdisciplinary applications and integration into commercial THz technologies.