Reeder, R., E. Velmre, and A. Udal. “Advances in Terahertz Technology With Emphasis on Quantum Cascade Lasers”. Elektronika Ir Elektrotechnika, vol. 104, no. 8, Oct. 2010, pp. 47-50, https://eejournal.ktu.lt/index.php/elt/article/view/9225.