[1] Tonouchi M. Cutting-edge terahertz technology[J]. Nature Photonics, 1, 97-105(2007).

[2] Dhillon S S, Vitiello M S, Linfield E H et al. The 2017 terahertz science and technology roadmap[J]. Journal of Physics D: Applied Physics, 50, 043001(2017).

[3] Koch M, Mittleman D M, Ornik J et al. Terahertz time-domain spectroscopy[J]. Nature Reviews Methods Primers, 3, 49(2023).

[4] Leitenstorfer A, Moskalenko A S, Kampfrath T et al. The 2023 terahertz science and technology roadmap[J]. Journal of Physics D: Applied Physics, 56, 223001(2023).

[5] Helal S, Sarieddeen H, Dahrouj H et al. Signal processing and machine learning techniques for terahertz sensing: an overview[J]. IEEE Signal Processing Magazine, 39, 42-62(2022).

[6] Lewis R A. A review of terahertz detectors[J]. Journal of Physics D: Applied Physics, 52, 433001(2019).

[7] Dean P, Valavanis A, Keeley J et al. Terahertz imaging using quantum cascade lasers—a review of systems and applications[J]. Journal of Physics D: Applied Physics, 47, 374008(2014).

[8] Hübers H W, Richter H, Wienold M. High resolution terahertz spectroscopy with quantum cascade lasers[J]. Journal of Applied Physics, 125, 151401(2019).

[9] Wang C X, You X H, Gao X Q et al. On the road to 6G: visions, requirements, key technologies, and testbeds[J]. IEEE Communications Surveys & Tutorials, 25, 905-974(2023).

[10] Köhler R, Tredicucci A, Beltram F et al. Terahertz semiconductor-heterostructure laser[J]. Nature, 417, 156-159(2002).

[11] Walther C, Fischer M, Scalari G et al. Quantum cascade lasers operating from 1.2 THz to 1.6 THz[J]. Applied Physics Letters, 91, 131122(2007).

[12] Li L H, Kundu I, Dean P et al. High-power GaAs/AlGaAs quantum cascade lasers with emission in the frequency range 4.7‒5.6 THz[C](2016).

[13] 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).

[14] Curwen C A, Reno J L, Williams B S. Broadband continuous single-mode tuning of a short-cavity quantum-cascade VECSEL[J]. Nature Photonics, 13, 855-859(2019).

[15] Jaidl M, Beiser M, Giparakis M et al. Ultrabroadband heterogeneous THz quantum cascade laser[J]. ACS Photonics, 10, 111-115(2023).

[16] Khalatpour A, Tam M C, Addamane S J et al. Enhanced operating temperature in terahertz quantum cascade lasers based on direct phonon depopulation[J]. Applied Physics Letters, 122, 161101(2023).

[17] Biasco S, Garrasi K, Castellano F et al. Continuous-wave highly-efficient low-divergence terahertz wire lasers[J]. Nature Communications, 9, 1122(2018).

[18] Betz A L, Boreiko R T, Williams B S et al. Frequency and phase-lock control of a 3 THz quantum cascade laser[J]. Optics Letters, 30, 1837-1839(2005).

[19] Danylov A A, Goyette T M, Waldman J et al. Frequency stabilization of a single mode terahertz quantum cascade laser to the kilohertz level[J]. Optics Express, 17, 7525-7532(2009).

[20] Rabanus D, Graf U U, Philipp M et al. Phase locking of a 1.5 Terahertz quantum cascade laser and use as a local oscillator in a heterodyne HEB receiver[J]. Optics Express, 17, 1159-1168(2009).

[21] Richter H, Pavlov S G, Semenov A D et al. Submegahertz frequency stabilization of a terahertz quantum cascade laser to a molecular absorption line[J]. Applied Physics Letters, 96, 071112(2010).

[22] Barbieri S, Gellie P, Santarelli G et al. Phase-locking of a 2.7-THz quantum cascade laser to a mode-locked erbium-doped fibre laser[J]. Nature Photonics, 4, 636-640(2010).

[23] Freeman J R, Ponnampalam L, Shams H et al. Injection locking of a terahertz quantum cascade laser to a telecommunications wavelength frequency comb[J]. Optica, 4, 1059-1064(2017).

[24] Vitiello M S, Consolino L, Bartalini S et al. Quantum-limited frequency fluctuations in a terahertz laser[J]. Nature Photonics, 6, 525-528(2012).

[25] Bartalini S, Consolino L, Cancio P et al. Frequency-comb-assisted terahertz quantum cascade laser spectroscopy[J]. Physical Review X, 4, 021006(2014).

[26] Wang F H, Nong H, Fobbe T et al. Short terahertz pulse generation from a dispersion compensated modelocked semiconductor laser[J]. Laser & Photonics Reviews, 11, 1770042(2017).

[27] Maineult W, Ding L, Gellie P et al. Microwave modulation of terahertz quantum cascade lasers: a transmission-line approach[J]. Applied Physics Letters, 96, 021108(2010).

[28] Micheletti P, Faist J, Olariu T et al. Regenerative terahertz quantum detectors[J]. APL Photonics, 6, 106102(2021).

[29] Burghoff D, Kao T Y, Han N R et al. Terahertz laser frequency combs[J]. Nature Photonics, 8, 462-467(2014).

[30] Vijayraghavan K, Jiang Y F, Jang M et al. Broadly tunable terahertz generation in mid-infrared quantum cascade lasers[J]. Nature Communications, 4, 2021(2013).

[31] Riepl J, Raab J, Abajyan P et al. Field-resolved high-order sub-cycle nonlinearities in a terahertz semiconductor laser[J]. Light: Science & Applications, 10, 246(2021).

[32] Raab J, Mezzapesa F P, Viti L et al. Ultrafast terahertz saturable absorbers using tailored intersubband polaritons[J]. Nature Communications, 11, 4290(2020).

[33] Consolino L, Nafa M, De Regis M et al. Quantum cascade laser based hybrid dual comb spectrometer[J]. Communications Physics, 3, 69(2020).

[34] Perraud J B, Guillet J P, Redon O et al. Shape-from-focus for real-time terahertz 3D imaging[J]. Optics Letters, 44, 483-486(2019).

[35] Liu H C, Song C Y, SpringThorpe A J et al. Terahertz quantum-well photodetector[J]. Applied Physics Letters, 84, 4068-4070(2004).

[36] Tan Z Y, Wan W J, Cao J C. Research progress in terahertz quantum-cascade lasers and quantum-well photodetectors[J]. Chinese Physics B, 29, 084212(2020).

[37] Jeannin M, Bonazzi T, Gacemi D et al. High temperature metamaterial terahertz quantum detector[J]. Applied Physics Letters, 117, 251102(2020).

[38] Chen Z, Gu L, Tan Z Y et al. Real-time video signal transmission over a terahertz communication link[J]. Chinese Optics Letters, 11, 112001(2013).

[39] Li H, Wan W J, Tan Z Y et al. 6.2-GHz modulated terahertz light detection using fast terahertz quantum well photodetectors[J]. Scientific Reports, 7, 3452(2017).

[40] Schneider H, Liu H C, Winnerl S et al. Terahertz two-photon quantum well infrared photodetector[J]. Optics Express, 17, 12279-12284(2009).

[41] Barbieri S, Alton J, Beere H E et al. 2.9 THz quantum cascade lasers operating up to 70 K in continuous wave[J]. Applied Physics Letters, 85, 1674-1676(2004).

[42] Wienold M, Schrottke L, Giehler M et al. Low-voltage terahertz quantum-cascade lasers based on LO-phonon-assisted interminiband transitions[J]. Electronics Letters, 45, 1030-1031(2009).

[43] Han Y J, Li L H, Grier A et al. Extraction-controlled terahertz frequency quantum cascade lasers with a diagonal LO-phonon extraction and injection stage[J]. Optics Express, 24, 28583-28593(2016).

[44] Kumar S, Chan C W I, Hu Q et al. A 1.8-THz quantum cascade laser operating significantly above the temperature of ℏω /kB[J]. Nature Physics, 7, 166-171(2011).

[45] Goodnick S M, Lugli P. Effect of electron-electron scattering on nonequilibrium transport in quantum-well systems[J]. Physical Review B, 37, 2578-2588(1988).

[46] Bonno O, Thobel J L, Dessenne F. Modeling of electron-electron scattering in Monte Carlo simulation of quantum cascade lasers[J]. Journal of Applied Physics, 97, 043702(2005).

[47] Lü J T, Cao J C. Monte Carlo simulation of hot phonon effects in resonant-phonon-assisted terahertz quantum-cascade lasers[J]. Applied Physics Letters, 88, 061119(2006).

[48] Callebaut H, Kumar S, Williams B S et al. Importance of electron-impurity scattering for electron transport in terahertz quantum-cascade lasers[J]. Applied Physics Letters, 84, 645-647(2004).

[49] Regnault N, Ferreira R, Bastard G. Broadening effects due to alloy scattering in a quantum cascade laser[J]. Physical Review B, 76, 165121(2007).

[50] Li T, Joshi R P, Fazi C. Monte Carlo evaluations of degeneracy and interface roughness effects on electron transport in AlGaN-GaN heterostructures[J]. Journal of Applied Physics, 88, 829-837(2000).

[51] Callebaut H, Kumar S, Williams B S et al. Analysis of transport properties of tetrahertz quantum cascade lasers[J]. Applied Physics Letters, 83, 207-209(2003).

[52] Indjin D, Harrison P, Kelsall R W et al. Mechanisms of temperature performance degradation in terahertz quantum-cascade lasers[J]. Applied Physics Letters, 82, 1347-1349(2003).

[53] Callebaut H, Hu Q. Importance of coherence for electron transport in terahertz quantum cascade lasers[J]. Journal of Applied Physics, 98, 104505(2005).

[54] Indjin D, Harrison P, Kelsall R W et al. Self-consistent scattering theory of transport and output characteristics of quantum cascade lasers[J]. Journal of Applied Physics, 91, 9019-9026(2002).

[55] Jacoboni C, Reggiani L. The Monte Carlo method for the solution of charge transport in semiconductors with applications to covalent materials[J]. Reviews of Modern Physics, 55, 645-705(1983).

[56] Dupont E, Fathololoumi S, Liu H C. Simplified density-matrix model applied to three-well terahertz quantum cascade lasers[J]. Physical Review B, 81, 205311(2010).

[57] Lee S C, Wacker A. Nonequilibrium Green's function theory for transport and gain properties of quantum cascade structures[J]. Physical Review B, 66, 245314(2002).

[58] Williams B S, Kumar S, Callebaut H et al. Terahertz quantum-cascade laser at λ≈100 μm using metal waveguide for mode confinement[J]. Applied Physics Letters, 83, 2124-2126(2003).

[59] Williams B S, Kumar S, Hu Q et al. Operation of terahertz quantum-cascade lasers at 164 K in pulsed mode and at 117 K in continuous-wave mode[J]. Optics Express, 13, 3331-3339(2005).

[60] Belkin M A, Fan J A, Hormoz S et al. Terahertz quantum cascade lasers with copper metal-metal waveguides operating up to 178 K[J]. Optics Express, 16, 3242-3248(2008).

[61] Han Y J, Li L H, Zhu J et al. Silver-based surface plasmon waveguide for terahertz quantum cascade lasers[J]. Optics Express, 26, 3814-3827(2018).

[62] Chan C W I, Hu Q, Reno J L. Ground state terahertz quantum cascade lasers[J]. Applied Physics Letters, 101, 151108(2012).

[63] Wade A, Fedorov G, Smirnov D et al. Magnetic-field-assisted terahertz quantum cascade laser operating up to 225 K[J]. Nature Photonics, 3, 41-45(2009).

[64] Li W J, Ma Y, Xu Y F et al. Continuous-wave single-mode quantum cascade laser at 5.1 THz based on graded sampled grating design[J]. Photonics Research, 10, 2686-2692(2022).

[65] Turčinková D, Scalari G, Castellano F et al. Ultra-broadband heterogeneous quantum cascade laser emitting from 2.2 to 3.2 THz[J]. Applied Physics Letters, 99, 191104(2011).

[66] Rösch M, Beck M, Süess M J et al. Heterogeneous terahertz quantum cascade lasers exceeding 1.9 THz spectral bandwidth and featuring dual comb operation[J]. Nanophotonics, 7, 237-242(2018).

[67] Rösch M, Scalari G, Beck M et al. Octave-spanning semiconductor laser[J]. Nature Photonics, 9, 42-47(2015).

[68] Li L H, Garrasi K, Kundu I et al. Broadband heterogeneous terahertz frequency quantum cascade laser[J]. Electronics Letters, 54, 1229-1231(2018).

[69] Qin Q, Reno J L, Hu Q. MEMS-based tunable terahertz wire-laser over 330 GHz[J]. Optics Letters, 36, 692-694(2011).

[70] Castellano F, Bianchi V, Li L H et al. Tuning a microcavity-coupled terahertz laser[J]. Applied Physics Letters, 107, 261108(2015).

[71] Xu L Y, Curwen C A, Hon P W C et al. Metasurface external cavity laser[J]. Applied Physics Letters, 107, 221105(2015).

[72] Brandstetter M, Deutsch C, Krall M et al. High power terahertz quantum cascade lasers with symmetric wafer bonded active regions[J]. Applied Physics Letters, 103, 171113(2013).

[73] Tan Z Y, Wang H Y, Wan W J et al. Dual-beam terahertz quantum cascade laser with >1 W effective output power[J]. Electronics Letters, 56, 1204-1206(2020).

[74] Curwen C A, Reno J L, Williams B S. Terahertz quantum cascade VECSEL with watt-level output power[J]. Applied Physics Letters, 113, 011104(2018).

[75] Jin Y, Reno J L, Kumar S. Phase-locked terahertz plasmonic laser array with 2 W output power in a single spectral mode[J]. Optica, 7, 708-715(2020).

[76] Bosco L, Franckié M, Scalari G et al. Thermoelectrically cooled THz quantum cascade laser operating up to 210 K[J]. Applied Physics Letters, 115, 010601(2019).

[77] Khalatpour A, Paulsen A K, Deimert C et al. High-power portable terahertz laser systems[J]. Nature Photonics, 15, 16-20(2021).

[78] Schneider H, Liu H C[M]. Quantum well infrared photodetectors: physics and applications, 45-80(2006).

[79] Gu L L, Zhang R, Tan Z Y et al. Terahertz quantum well photo-detectors: grating versus 45° facet coupling[J]. Journal of Physics D: Applied Physics, 47, 165101(2014).

[80] Franke C, Walther M, Helm M et al. Two-photon quantum well infrared photodetectors below 6 THz[J]. Infrared Physics & Technology, 70, 30-33(2015).

[81] Wang H X, Zhang R, Wang F et al. Two-colour THz quantum well photodetectors[J]. Electronics Letters, 53, 1129-1130(2017).

[82] Wang H X, Fu Z L, Shao D X et al. Broadband bias-tunable terahertz photodetector using asymmetric GaAs/AlGaAs step multi-quantum well[J]. Applied Physics Letters, 113, 171107(2018).

[83] Guo X G, Cao J C, Zhang R et al. Recent progress in terahertz quantum-well photodetectors[J]. IEEE Journal of Selected Topics in Quantum Electronics, 19, 8500508(2013).

[84] Zhang R, Fu Z L, Gu L L et al. Terahertz quantum well photodetectors with reflection-grating couplers[J]. Applied Physics Letters, 105, 231123(2014).

[85] Zhang R, Shao D X, Fu Z L et al. Terahertz quantum well photodetectors with metal-grating couplers[J]. IEEE Journal of Selected Topics in Quantum Electronics, 23, 3800407(2017).

[86] Palaferri D, Todorov Y, Chen Y N et al. Patch antenna terahertz photodetectors[J]. Applied Physics Letters, 106, 161102(2015).

[87] Guo X G, Tan Z Y, Cao J C et al. Many-body effects on terahertz quantum well detectors[J]. Applied Physics Letters, 94, 201101(2009).

[88] Jia J Y, Wang T M, Zhang Y H et al. High-temperature photon-noise-limited performance terahertz quantum-well photodetectors[J]. IEEE Transactions on Terahertz Science and Technology, 5, 715-724(2015).

[89] Hübers H W, Pavlov S G, Richter H et al. High-resolution gas phase spectroscopy with a distributed feedback terahertz quantum cascade laser[J]. Applied Physics Letters, 89, 061115(2006).

[90] Consolino L, Bartalini S, Beere H E et al. THz QCL-based cryogen-free spectrometer for in situ trace gas sensing[J]. Sensors, 13, 3331-3340(2013).

[91] Eichholz R, Richter H, Wienold M et al. Frequency modulation spectroscopy with a THz quantum-cascade laser[J]. Optics Express, 21, 32199-32206(2013).

[92] Hagelschuer T, Wienold M, Richter H et al. Terahertz gas spectroscopy through self-mixing in a quantum-cascade laser[J]. Applied Physics Letters, 109, 191101(2016).

[93] Han Y J, Partington J, Chhantyal-Pun R et al. Gas spectroscopy through multimode self-mixing in a double-metal terahertz quantum cascade laser[J]. Optics Letters, 43, 5933-5936(2018).

[94] Ren Y, Hovenier J N, Higgins R et al. High-resolution heterodyne spectroscopy using a tunable quantum cascade laser around 3.5 THz[J]. Applied Physics Letters, 98, 231109(2011).

[95] Richter H, Wienold M, Schrottke L et al. 4.7-THz local oscillator for the GREAT heterodyne spectrometer on SOFIA[J]. IEEE Transactions on Terahertz Science and Technology, 5, 539-545(2015).

[96] Sampaolo A, Patimisco P, Giglio M et al. Improved tuning fork for terahertz quartz-enhanced photoacoustic spectroscopy[J]. Sensors, 16, 439(2016).

[97] Hayton D J, Khudchenko A, Pavelyev D G et al. Phase locking of a 3.4 THz third-order distributed feedback quantum cascade laser using a room-temperature superlattice harmonic mixer[J]. Applied Physics Letters, 103, 051115(2013).

[98] Bulcha B T, Hesler J L, Drakinskiy V et al. Design and characterization of 1.8‒3.2 THz Schottky-based harmonic mixers[J]. IEEE Transactions on Terahertz Science and Technology, 6, 737-746(2016).

[99] Ren Y, Hovenier J N, Cui M et al. Frequency locking of single-mode 3.5-THz quantum cascade lasers using a gas cell[J]. Applied Physics Letters, 100, 041111(2012).

[100] Darmo J, Tamosiunas V, Fasching G et al. Imaging with a terahertz quantum cascade laser[J]. Optics Express, 12, 1879-1884(2004).

[101] Tan Z Y, Gu L, Xu T H et al. Real-time reflection imaging with terahertz camera and quantum-cascade laser[J]. Chinese Optics Letters, 12, 070401(2014).

[102] de Cumis U S, Xu J H, Masini L et al. Terahertz confocal microscopy with a quantum cascade laser source[J]. Optics Express, 20, 21924-21931(2012).

[103] Oda N, Ishi T, Morimoto T et al. Real-time transmission-type terahertz microscope with palm size terahertz camera and compact quantum cascade laser[J]. Proceedings of SPIE, 8496, 84960Q(2012).

[104] 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).

[105] Rothbart N, Richter H, Wienold M et al. Fast 2-D and 3-D terahertz imaging with a quantum-cascade laser and a scanning mirror[J]. IEEE Transactions on Terahertz Science and Technology, 3, 617-624(2013).

[106] Qiu F C, Tan Z Y, Fu Z L et al. Reflective scanning imaging based on a fast terahertz photodetector[J]. Optics Communications, 427, 170-174(2018).

[107] Lee A W M, Williams B S, Kumar S et al. Real-time imaging using a 4.3-THz quantum cascade laser and a 320×240 microbolometer focal-plane array[J]. IEEE Photonics Technology Letters, 18, 1415-1417(2006).

[108] Lee A W M, Qin Q, Kumar S et al. Real-time terahertz imaging over a standoff distance (>25 meters)[J]. Applied Physics Letters, 89, 141125(2006).

[109] Fu Z L, Gu L L, Guo X G et al. Frequency up-conversion photon-type terahertz imager[J]. Scientific Reports, 6, 25383(2016).

[110] Yang M W, Ji H B, Tan Z Y et al. Terahertz joint analyzer with imaging and spetrum detection[J]. Acta Optica Sinica, 36, 0611004(2016).

[111] Danylov A A, Goyette T M, Waldman J et al. Terahertz inverse synthetic aperture radar (ISAR) imaging with a quantum cascade laser transmitter[J]. Optics Express, 18, 16264-16272(2010).

[112] Ravaro M, Jagtap V, Santarelli G et al. Continuous-wave coherent imaging with terahertz quantum cascade lasers using electro-optic harmonic sampling[J]. Applied Physics Letters, 102, 091107(2013).

[113] 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).

[114] Xie Y, Wang Y X, Li L H et al. Realization of high depth resolution using two-beam self-mixing interferometry with a terahertz quantum cascade laser[J]. Optics Communications, 545, 129737(2023).

[115] Qi X Q, Bertling K, Stark M S et al. Terahertz imaging of human skin pathologies using laser feedback interferometry with quantum cascade lasers[J]. Biomedical Optics Express, 14, 1393-1410(2023).

[116] Grant P D, Laframboise S R, Dudek R et al. Terahertz free space communications demonstration with quantum cascade laser and quantum well photodetector[J]. Electronics Letters, 45, 952-954(2009).

[117] Chen Z, Tan Z Y, Han Y J et al. Wireless communication demonstration at 4.1 THz using quantum cascade laser and quantum well photodetector[J]. Electronics Letters, 47, 1002-1004(2011).

[118] Barbieri S, Maineult W, Dhillon S S et al. 13 GHz direct modulation of terahertz quantum cascade lasers[J]. Applied Physics Letters, 91, 143510(2007).

[119] Dunn A, Poyser C, Dean P et al. High-speed modulation of a terahertz quantum cascade laser by coherent acoustic phonon pulses[J]. Nature Communications, 11, 835(2020).

[120] Tan Z Y, Li H, Wan W J et al. Direct detection of a fast modulated terahertz light with a spectrally matched quantum-well photodetector[J]. Electronics Letters, 53, 91-93(2017).

[121] Wang F H, Pistore V, Riesch M et al. Ultrafast response of harmonic modelocked THz lasers[J]. Light: Science & Applications, 9, 51(2020).

[122] Pistore V, Nong H, Vigneron P B et al. Millimeter wave photonics with terahertz semiconductor lasers[J]. Nature Communications, 12, 1427(2021).

[123] di Gaspare A, Pogna E A A, Salemi L et al. Tunable, grating-gated, graphene-on-polyimide terahertz modulators[J]. Advanced Functional Materials, 31, 2008039(2021).

[124] Lu Q Y, Wang F H, Wu D H et al. Room temperature terahertz semiconductor frequency comb[J]. Nature Communications, 10, 2403(2019).

[125] Cappelli F, Consolino L, Campo G et al. Retrieval of phase relation and emission profile of quantum cascade laser frequency combs[J]. Nature Photonics, 13, 562-568(2019).

[126] Consolino L, Nafa M, Cappelli F et al. Fully phase-stabilized quantum cascade laser frequency comb[J]. Nature Communications, 10, 2938(2019).

[127] Li H, Yan M, Wan W J et al. Graphene-coupled terahertz semiconductor lasers for enhanced passive frequency comb operation[J]. Advanced Science, 6, 1970120(2019).

[128] Meng B, Hinkov B, Biavan N M L et al. Terahertz intersubband electroluminescence from nonpolar m-plane ZnO quantum cascade structures[J]. ACS Photonics, 8, 343-349(2021).

[129] Zeng Y Q, Chattopadhyay U, Zhu B F et al. Electrically pumped topological laser with valley edge modes[J]. Nature, 578, 246-250(2020).

[130] Feng L, El-Ganainy R, Ge L. Non-Hermitian photonics based on parity-time symmetry[J]. Nature Photonics, 11, 752-762(2017).

[131] Harari G, Bandres M A, Lumer Y. Topological insulator laser: theory[J]. Science, 359, eaar4003(2018).

[132] Han S, Chua Y, Zeng Y Q et al. Photonic Majorana quantum cascade laser with polarization-winding emission[J]. Nature Communications, 14, 707(2023).