[1] Scalari G, Walther C, Fischer M et al. THz and sub-THz quantum cascade lasers[J]. Laser & Photonics Review, 3, 45-66(2009).

[2] Williams B S, Kumar S, Hu Q et al. High-power terahertz quantum-cascade lasers[J]. Electronics Letters, 42, 89-91(2006).

[3] Li L H, Chen L, Freeman J R et al. Multi-Watt high-power THz frequency quantum cascade lasers[J]. Electronics Letters, 53, 799-800(2017).

[4] Lim Y L, Taimre T, Bertling K et al. High-contrast coherent terahertz imaging of porcine tissue via swept-frequency feedback interferometry[J]. Biomedical Optics Express, 5, 3981(2014).

[5] Chhantyal-Pun R, Valavanis A, Keeley J T et al. Gas spectroscopy with integrated frequency monitoring through self-mixing in a terahertz quantum-cascade laser[J]. Optics Letters, 43, 2225-2228(2018).

[6] Taimre T, Bertling K et al. Swept-frequency feedback interferometry using terahertz frequency QCLs: a method for imaging and materials analysis[J]. Optics Express, 21, 22194-22205(2013).

[7] Green R P, Xu J H, Mahler L et al. Linewidth enhancement factor of terahertz quantum cascade lasers[J]. Applied Physics Letters, 92, 071106(2008).

[8] Dean P, Leng Lim Y, Valavanis A et al. Terahertz imaging through self-mixing in a quantum cascade laser[J]. Optics Letters, 36, 2587(2011).

[9] Dean P, Valavanis A, Keeley J et al. Coherent three-dimensional terahertz imaging through self-mixing in a quantum cascade laser[J]. Applied Physics Letters, 103, 181112(2013).

[10] Keeley J, Dean P, Valavanis A et al. Three-dimensional terahertz imaging using swept-frequency feedback interferometry with a quantum cascade laser[J]. Optics Letters, 40, 994-997(2015).

[11] Degl'Innocenti R, Wallis R, Wei B B et al. Terahertz nanoscopy of plasmonic resonances with a quantum cascade laser[J]. ACS Photonics, 4, 2150-2157(2017).

[12] Zuo Z G, Ling F R, Wang P et al. Hyperfine spectrum measurement of an optically pumped far-infrared laser with a Michelson interferometer[J]. Laser Physics Letters, 10, 055004(2013).

[13] Liu W X, Wu D, Wang Y X et al. Terahertz frequency measurement of far-infrared laser with an improvement of Martin-Puplett interferometer[J]. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 614, 313-318(2010).

[14] Gaal P, Raschke M B, Reimann K et al. Measuring optical frequencies in the 0-40 THz range with non-synchronized electro-optic sampling[J]. Nature Photonics, 1, 577-580(2007).

[15] Yokoyama S, Nakamura R, Nose M et al. Terahertz spectrum analyzer based on a terahertz frequency comb[J]. Optics Express, 16, 13052-13061(2008).

[16] Lang R, Kobayashi K. External optical feedback effects on semiconductor injection laser properties[J]. IEEE Journal of Quantum Electronics, 16, 347-355(1980).

[17] Katz J, Margalit S, Harder C et al. The intrinsic electrical equivalent circuit of a laser diode[J]. IEEE Journal of Quantum Electronics, 17, 4-7(1981).

[18] Xi J T, Yu Y G, Chicharo J F et al. Estimating the parameters of semiconductor lasers based on weak optical feedback self-mixing interferometry[J]. IEEE Journal of Quantum Electronics, 41, 1058-1064(2005).

[19] Keeley J, Freeman J, Bertling K et al. Measurement of the emission spectrum of a semiconductor laser using laser-feedback interferometry[J]. Scientific Reports, 7, 7236-7245(2017).

[20] Valavanis A, Dean P, Lim Y L et al. Self-mixing interferometry with terahertz quantum cascade lasers[J]. IEEE Sensors Journal, 13, 37-43(2013).

[21] Vitiello M S, Tredicucci A. Tunable emission in THz quantum cascade lasers[J]. IEEE Transactions on Terahertz Science and Technology, 1, 76-84(2011).