Sirkeli, V.P., and H.L. Hartnagel. “ZnO-Based Terahertz Quantum Cascade Lasers”. Opto-Electronics Review 27, no. 2 (May 6, 2019): 119–122. Accessed August 18, 2026. https://wydawnictwo.pan.pl/index.php/opelre/article/view/645.