Characterizing absolute gain of quantum cascade lasers using terahertz time-domain spectroscopy measurements

Zhenyang Xiao; Mithun Roy; Md Istiak Khan; David Burghoff

doi:10.1117/12.3028268

1 October 2024 Characterizing absolute gain of quantum cascade lasers using terahertz time-domain spectroscopy measurements

Zhenyang Xiao, Mithun Roy, Md Istiak Khan, David Burghoff

Author Affiliations +

Proceedings Volume 13141, Terahertz Emitters, Receivers, and Applications XV; 1314104 (2024) https://doi.org/10.1117/12.3028268
Event: Optical Engineering + Applications, 2024, San Diego, California, United States

Abstract

Terahertz Quantum Cascade Lasers (QCLs) are crucial for advancing research due to their high-power output, compact size, and efficiency. These lasers, designed through precise intersubband structure engineering, often show experimental outcomes that diverge from theoretical prediction. This discrepancy highlights the need for experimental gain characterization of QCLs. Using terahertz time-domain spectroscopy and a uniquely structured QCL with two beam paths of identical curvature but different lengths, self-referenced gain measurements were conducted across various temperatures and biasing voltages. A dispersion correction technique was used to distinguish signals from the two paths. The gain profile was extracted by analyzing the spectra of pulses through these different paths, providing an accurate gain profile by negating the zero-bias loss profile’s impact. At 23 K, an absorption peak was identified at 2.37 THz under low bias, shifting to lower frequencies with increased bias, aligning with density matrix simulations. Beyond the lasing threshold, the peak gain at 3.2 THz was consistently around 0 cm⁻¹ for all bias levels. These findings underscore the self-referenced method’s significance in extracting absolute gain and dispersion information, enhancing device performance understanding.

Conference Presentation

Citation Download Citation

Zhenyang Xiao, Mithun Roy, Md Istiak Khan, and David Burghoff "Characterizing absolute gain of quantum cascade lasers using terahertz time-domain spectroscopy measurements", Proc. SPIE 13141, Terahertz Emitters, Receivers, and Applications XV, 1314104 (1 October 2024); https://doi.org/10.1117/12.3028268

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