[1] [1] Li W F, Guo B S, Shi W. Progress of terahertz parametric oscillator [J]. Laser & Optoelectronics Progress, 2014, 51(9): 090005.

[2] [2] Liu L, Li X, Liu T, et al. Progress of terahertz wave parametric oscillator [J]. Laser & Optoelectronics Progress, 2012, 49(9): 090001.

[3] [3] Lee A J, Spence D J, Pask H M. Terahertz sources based on stimulated polariton scattering [J]. Progress in Quantum Electronics, 2020, 71: 100254.

[4] [4] Kawase K, Shikata J I, Ito H. Terahertz wave parametric source [J]. Journal of Physics D: Applied Physics, 2002, 35(3): R1-R14.

[5] [5] Zang J. Study on Spatial Intensity Distribution of Terahertz Parameter Source and Stokes Parametric Oscillator of KTA Crystal [D]. Qindao: Shandong University, 2019.

[6] [6] Huang K. On the interaction between the radiation field and ionic crystals [J]. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 1951, 208(1094): 352-365.

[7] [7] Fano U. Atomic theory of electromagnetic interactions in dense materials [J]. Physical Review, 1956, 103(5): 1202-1218.

[8] [8] Hopfield J J. Theory of the contribution of excitons to the complex dielectric constant of crystals [J]. Physical Review, 1958, 112(5): 1555-1567.

[9] [9] Loudon R. Theory of stimulated Raman scattering from lattice vibrations [J]. Proceedings of the Physical Society, 1963, 82(3): 393-400.

[10] [10] Barker A S. Infrared lattice vibrations and dielectric dispersion in corundum [J]. Physical Review, 1963, 132(4): 1474-1481.

[11] [11] Shen Y R. Theory of stimulated Raman effect.II [J]. Physical Review, 1965, 138(6A): 1741-1746.

[12] [12] Sussman S S. Tunable Light Scattering From Transverse Optical Modes in Lithium Niobate [D]. California: Stanford University, 1970.

[13] [13] Henry C H, Hopfield J J. Raman scattering by polaritons [J]. Physical Review Letters, 1965, 15(25): 964-966.

[14] [14] Henry C H, Garrett C G B. Theory of parametric gain near a lattice resonance [J]. Physical Review, 1968, 171(3): 1058-1064.

[15] [15] Barker A S, Loudon R. Dielectric properties and optical phonons in LiNbO3 [J]. Physical Review, 1967, 158(2): 433-445.

[16] [16] Barker A S, Loudon R. Response functions in the theory of Raman scattering by vibrational and polariton modes in dielectric crystals [J]. Reviews of Modern Physics, 1972, 44(1): 18-47.

[17] [17] Johnston W D, Kaminow I P. Contributions to optical nonlinearity in GaAs as determined from Raman scattering efficiencies [J]. Physical Review, 1969, 188(3): 1209-1211.

[18] [18] Johnston W D. Nonlinear optical coefficients and the Raman scattering efficiency of LO and TO phonons in acentric insulating crystals [J]. Physical Review B, 1970, 1(8): 3494-3503.

[19] [19] Kleinman D A. Nonlinear dielectric polarization in optical media [J]. Physical Review, 1962, 126(6): 1977-1979.

[20] [20] Boyd G D, Bridges T J, Pollack M A, et al. Microwave nonlinear susceptibilities due to electronic and ionic anharmonicities in acentric crystals [J]. Physical Review Letters, 1971, 26(7): 387-390.

[21] [21] Schwarz U T, Maier M. Damping mechanisms of phonon polaritons, exploited by stimulated Raman gain measurements [J]. Physical Review B, 1998, 58(2): 766-775.

[22] [22] Choy M M, Byer R L. Accurate second-order susceptibility measurements of visible and infrared nonlinear crystals [J]. Physical Review B, 1976, 14(4): 1693-1706.

[23] [23] Theis W M, Norris G B, Porter M D. High resolution infrared measurements of the OH-bands in KTiOPO4 [J]. Applied Physics Letters, 1985, 46(11): 1033-1035.

[24] [24] Kaminow I P, Johnston W D. Quantitative determination of sources of the electro-optic effect in LiNbO3 and LiTaO3 [J]. Physical Review, 1967, 160(3): 520-522.

[25] [25] Rüsing M, Eigner C, Mackwitz P, et al. Identification of ferroelectric domain structure sensitive phonon modes in potassium titanyl phosphate: A fundamental study [J]. Journal of Applied Physics, 2016, 119(4): 044103.

[27] [27] Kawase K, Sato M, Taniuchi T, et al. Coherent tunable THz-wave generation from LiNbO3 with monolithic grating coupler [J]. Applied Physics Letters, 1996, 68(18): 2483-2485.

[28] [28] Kawase K, Sato M, Nakamura K, et al. Unidirectional radiation of widely tunable THz wave using a prism coupler under noncollinear phase matching condition [J]. Applied Physics Letters, 1997, 71(6): 753-755.

[29] [29] Li Z Y, Bing P B, Yuan S, et al. Terahertz wave parametric oscillations at polariton resonance using a MgO:LiNbO3 crystal [J]. Applied Optics, 2015, 54(18): 5645-5649.

[30] [30] Walsh D, Stothard D J M, Edwards T J, et al. Injection-seeded intracavity terahertz optical parametric oscillator [J]. Journal of the Optical Society of America B, 2009, 26(6): 1196-1202.

[31] [31] Henry C H, Hopfield J J. Raman scattering by polaritons [J]. Physical Review Letters, 1965, 15(25): 964-966.

[32] [32] Kurtz S K, Giordmaine J A. Stimulated Raman scattering by polaritons [J]. Physical Review Letters, 1969, 22(5): 192-196.

[33] [33] Gelbwachs J, Pantell R H, Puthoff H E, et al. A tunable stimulated Raman oscillator [J]. Applied Physics Letters, 1969, 14(9): 258-262.

[34] [34] Yarborough J M, Sussman S S, Purhoff H E, et al. Efficient, tunable optical emission from LiNbO3 without a resonator [J]. Applied Physics Letters, 1969, 15(3): 102-105.

[35] [35] Wang W T, Cong Z H, Chen X H, et al. Terahertz parametric oscillator based on KTiOPO4 crystal [J]. Optics Letters, 2014, 39(13): 3706-3709.

[36] [36] Wang W T. Research on New Terahertz Parametric Sources [D]. Jinan: Shandong University, 2015.

[37] [37] Yan C, Wang Y Y, Xu D G, et al. Green laser induced terahertz tuning range expanding in KTiOPO4 terahertz parametric oscillator [J]. Applied Physics Letters, 2016, 108(1): 011107.

[38] [38] Jia C Y, Zhang X Y, Cong Z H, et al. Theoretical and experimental study on a large energy potassium titanyl phosphate terahertz parametric source [J]. Optics & Laser Technology, 2020, 121: 105817.

[39] [39] Jia C Y. Theoretical and Experimental Study on a High Performance Potassium Titanyl Phosphate Terahertz Parametric Source [D]. Qingdao: Shandong University, 2019.

[40] [40] Wang Z C, Zhang X Y, Cong Z H, et al. Tunable Stokes laser based on KTiOPO4 crystal [J]. Crystals, 2020, 10(11): 974.

[41] [41] Wu M H, Tsai W C, Chiu Y C, et al. Generation of ～100 kW narrow-line far-infrared radiation from a KTP off-axis THz parametric oscillator [J]. Optica, 2019, 6(6): 723-730.

[42] [42] Yan C, Wang Y Y, Xu D G, et al. Enhanced stimulated polariton scattering in KTiOPO4 terahertz parametric oscillator based on green laser pumping [C]. st International Conference on Infrared, Millimeter, and Terahertz Waves, 2016.

[43] [43] Kugel G E, Brehat F, Wyncke B, et al. The vibrational spectrum of a KTiOPO4 single crystal studied by Raman and infrared reflectivity spectroscopy [J]. Journal of Physics C:Solid State Physics, 1988, 21(32): 5565-5583.

[44] [44] Zang J, Cong Z H, Chen X H, et al. Tunable KTA Stokes laser based on stimulated polariton scattering and its intracavity frequency doubling [J]. Optics Express, 2016, 24(7): 7558-7565.

[45] [45] Wang W T, Cong Z H, Liu Z J, et al. THz-wave generation via stimulated polariton scattering in KTiOAsO4 crystal [J]. Optics Express, 2014, 22(14): 17092-17098.

[46] [46] Xu J J, Zhang X Y, Cong Z H, et al. Tunable Nd3+: YAG/KTiOAsO4 Raman lasers [J]. Chinese Journal of Lasers, 2020, 47(6): 0601002.

[47] [47] Xu J J. Study on Tunable Raman Lasers of KTiOPO4 and KTiOAsO4 Crystals [D]. Qingdao: Shandong University, 2020.

[48] [48] Watson G H. Polarized Raman spectra of KTiOAsO4 and isomorphic nonlinear-optical crystals [J]. Journal of Raman Spectroscopy, 1991, 22(11): 705-713.

[49] [49] Ortega T A, Pask H M, Spence D J, et al. Stimulated polariton scattering in an intracavity RbTiOPO4 crystal generating frequency-tunable THz output [J]. Optics Express, 2016, 24(10): 10254-10264.

[50] [50] Gao F L, Zhang X Y, Cong Z H, et al. Terahertz parametric oscillator with the surface-emitted configuration in RbTiOPO4 crystal [J]. Optics & Laser Technology, 2018, 104: 37-42.

[51] [51] Gao F L, Zhang X Y, Cong Z H, et al. Tunable Stokes laser based on the cascaded stimulated polariton scattering and stimulated Raman scattering in RbTiOPO4 crystal [J]. Optics Letters, 2020, 45(4): 861-864.

[52] [52] Gao F L. Studies of Terahertz Parametric Source Based on RbTiOPO4 Crystal [D]. Qingdao: Shandong University, 2020.

[53] [53] Gao F L, Zhang X Y, Cong Z H, et al. High average power diode-side-pumped intracavity terahertz parametric source based on stimulated polariton scattering in RbTiOPO4 crystal [J]. IEEE Photonics Journal, 2020, 12(2): 1400109.

[54] [54] Ortega T A. Frequency Extension of Solid-State Terahertz Lasers [D]. Sydney: Macquarie University, 2017.

[55] [55] Faust W L, Henry C H. Mixing of visible and near-resonance infrared light in GaP [J]. Physical Review Letters, 1966, 17(25): 1265-1268.

[56] [56] Faust W L, Henry C H, Eick R H. Dispersion in the nonlinear susceptibility of GaP near the reststrahl band [J]. Physical Review, 1968, 173(3): 781-786.

[57] [57] Barker A S. Dielectric dispersion and phonon line shape in gallium phosphide [J]. Physical Review, 1968, 165(3): 917-922.

[58] [58] Nishizawa J, Suto K. Semiconductor Raman laser [J]. Journal of Applied Physics, 1980, 51(5): 2429-2431.

[59] [59] Gorelik V S, Katyba G M. Generation of terahertz radiation in cubic non-centrosymmetric crystals [J]. Bulletin of the Lebedev Physics Institute, 2014, 41(5): 127-134.

[60] [60] Scott J F, Cheesman L E, Porto S P S. Polariton spectrum of α-quartz [J]. Physical Review, 1967, 162(3): 834-840.

[61] [61] Biraud-Laval S, Reinisch R, Paraire N, et al. Raman-susceptibility, damping-constant, and oscillator-strength determination from stimulated polaritons in quartz [J]. Physical Review B, 1976, 13(4): 1797-1801.

[62] [62] Sun B, Bai X P, Liu J S, et al. Investigation of a terahertz-wave parametric oscillator using LiTaO3 with the pump-wavelength tuning method [J]. Laser Physics, 2014, 24(3): 035402.

[63] [63] Chang T S, Johnson B C, Amzallag E, et al. Temperature dependence of polariton dispersion in LiTaO3 [J]. Optics Communications, 1971, 4(1): 72-74.

[64] [64] Allan D, Cracknell A P. Polaritons in LiTaO3 [J]. Journal of Physics C : Solid State Physics, 1977, 10(1): 123-136.

[65] [65] Amzallag E, Chang T S, Johnson B C, et al. Stimulated Raman and polariton scattering in LiIO3 [J]. Journal of Applied Physics, 1971, 42(8): 3251-3252.

[66] [66] Kulevsky L A, Polivanov Y N, Poluektov S N. Light scattering by polaritons in LiIO3 [J]. Journal of Raman Spectroscopy, 1975, 3(2/3): 239-254.

[67] [67] Zvirgzds J A, Habbal F, Nicola J H, et al. Polariton scattering in potassium dihydrogen phosphate KDP [J]. Physical Review B, 1979, 19(2): 1178-1182.

[68] [68] Kawase K, Shikata J, Minamide H, et al. Arrayed silicon prism coupler for a terahertz-wave parametric oscillator [J]. Applied Optics, 2001, 40(9): 1423-1426.

[69] [69] Imai K, Kawase K, Shikata J I, et al. Injection-seeded terahertz-wave parametric oscillator [J]. Applied Physics Letters, 2001, 78(8): 1026-1028.

[70] [70] Kawase K, Minamide H, Imai K, et al. Injection-seeded terahertz-wave parametric generator with wide tunability [J]. Applied Physics Letters, 2002, 80(2): 195-197.

[71] [71] Ikari T, Zhang X B, Minamide H, et al. THz-wave parametric oscillator with a surface-emitted configuration [J]. Optics Express, 2006, 14(4): 1604-1610.

[72] [72] Minamide H, Ikari T, Ito H. Frequency-agile terahertz-wave parametric oscillator in a ring-cavity configuration [J]. Review of Scientific Instruments, 2009, 80(12): 123104.

[73] [73] Walsh D, Stothard D J M, Edwards T J, et al. Injection-seeded intracavity terahertz optical parametric oscillator [J]. Journal of the Optical Society of America B, 2009, 26(6): 1196-1202.

[74] [74] Ikari T, Guo R X, Minamide H, et al. Energy scalable terahertz-wave parametric oscillator using surface-emitted configuration [J]. Journal of the European Optical Society-Rapid Publications, 2010, 5: 10054.

[75] [75] Minamide H, Hayashi S, Nawata K, et al. Kilowatt-peak terahertz-wave generation and sub-femtojoule terahertz-wave pulse detection based on nonlinear optical wavelength-conversion at room temperature [J]. Journal of Infrared, Millimeter, and Terahertz Waves, 2014, 35(1): 25-37.

[76] [76] Tang G Q, Zhang X Y, Cong Z H, et al. Terahertz parametric source generating pulse energy of 6.5 μJ at 1.74 THz [C]. th International Conference on Infrared, Millimeter, and Terahertz Waves, 2014.

[77] [77] Wang W T, Zhang X Y, Wang Q P, et al. Multiple-beam output of a surface-emitted terahertz-wave parametric oscillator by using a slab MgO:LiNbO3 crystal [J]. Optics Letters, 2014, 39(4): 754-757.

[78] [78] Tang G Q, Cong Z H, Qin Z G, et al. Energy scaling of terahertz-wave parametric sources [J]. Optics Express, 2015, 23(4): 4144-4152.

[79] [79] Tang G Q. The Studies of High Energy Nanosecond Terahertz Parametric Sources [D]. Jinan: Shandong University, 2015.

[80] [80] Yang Z, Wang Y Y, Xu D G, et al. THz wave parametric oscillator with a surface-emitted ring-cavity configuration [C]. Infrared, Millimeter-Wave, and Terahertz Technologies IV, 2016.

[81] [81] Stothard D J M, Edwards T J, Walsh D, et al. Line-narrowed, compact, and coherent source of widely tunable terahertz radiation [J]. Applied Physics Letters, 2008, 92(14): 141105.

[82] [82] Lee A, He Y B, Pask H. Frequency-tunable THz source based on stimulated polariton scattering in Mg:LiNbO3 [J]. IEEE Journal of Quantum Electronics, 2013, 49(3): 357-364.

[83] [83] Lee A J, Pask H M. Continuous wave, frequency-tunable terahertz laser radiation generated via stimulated polariton scattering [J]. Optics Letters, 2014, 39(3): 442-445.

[84] [84] Warrier A M, Li R, Lin J P, et al. Tunable terahertz generation in the picosecond regime from the stimulated polariton scattering in a LiNbO3 crystal [J]. Optics Letters, 2016, 41(18): 4409-4412.

[85] [85] Moriguchi Y, Nawata K, Takida Y, et al. High repetition-rate, widely tunable, injection-seeded terahertz-wave parametric generator [C]. International Conference on Infrared, Millimeter, and Terahertz Waves, 2017.

[86] [86] Ortega T A, Pask H M, Spence D J, et al. THz polariton laser using an intracavity Mg:LiNbO3 crystal with protective Teflon coating [J]. Optics Express, 2017, 25(4): 3991-3999.

[87] [87] Lee A J, Spence D J, Pask H M. Tunable THz polariton laser based on 1342 nm wavelength for enhanced terahertz wave extraction [J]. Optics Letters, 2017, 42(14): 2691-2694.

[88] [88] Ortega T A, Pask H M, Spence D J, et al. Tunable 3-6 THz polariton laser exceeding 0.1 mW average output power based on crystalline RbTiOPO4 [J]. IEEE Journal of Selected Topics in Quantum Electronics, 2018, 24(5): 5100806.

[89] [89] Zheng Y M, Lee A, Spence D, et al. Linewidth-narrowing of a continuous wave terahertz polariton laser using an intracavity etalon [J]. Optics Letters, 2020, 45(1): 157-160.

[90] [90] Gao F L, Zhang X Y, Cong Z H, et al. Enhancement of intracavity-pumped terahertz parametric oscillator power by adopting diode-side pumped configuration based on KTiOPO4 crystal [J]. Crystals, 2019, 9(12): 666.

[91] [91] Spence D J, Pask H M, Lee A J. Analytic theory for lasers based on stimulated polariton scattering [J]. Journal of the Optical Society of America B, 2019, 36(6): 1706-1715.

[92] [92] Qin Y, Li Z Y, Yan Q, et al. Numerical modeling of an injection-seeded terahertz-wave parametric generator [J]. Journal of Infrared, Millimeter, and Terahertz Waves, 2020, 41(3): 276-290.

[93] [93] Qin Y, Li Z Y, Yan Q, et al. A model of terahertz parametric process including spontaneous parametric down-conversion [J]. Journal of Infrared, Millimeter, and Terahertz Waves, 2021, 42(6): 656-670.

[94] [94] Zang J, Wu D, Zhang X Y, et al. The investigation on the beam spatial intensity distributions in the injection-seeded terahertz parametric generator [J]. IEEE Photonics Journal, 2019, 11(2): 1400211.

[95] [95] Wang P, Zhang X Y, Cong Z H, et al. Modeling of intracavity-pumped Q-switched terahertz parametric oscillators based on stimulated polariton scattering [J]. Optics Express, 2020, 28(5): 6966-6980.

[96] [96] Wang P. Theoretical and Experimental Study on Intracavity Terahertz Parametric Oscillator [D]. Qingdao: Shandong University, 2020.

[97] [97] Degnan J J. Theory of the optimally coupled Q-switched laser [J]. IEEE Journal of Quantum Electronics, 1989, 25(2): 214-220.

[98] [98] Wang Z C, Fan S Z, Chen X H, et al. Modeling for extracavity-pumped terahertz parametric oscillators [J]. Optics Express, 2022, 30(16): 29518-29530.