Research On High-power THz-wave Radiation Sources Based On Nonlinear Optics

THz-wave has great scientific research values and wide applications in imaging, material detection, environmental monitoring, communication, astronomy, life sciences, national defense security and so on. THz-wave parametric oscillator（TPO） based on stimulated polariton scattering has many advantages, such as high efficient,coherent,tuning,narrow linewidth, compactness and room temperature operation. THz-wave generation based on maximal atomic coherence between energy levels which are forbidden transition provides the promising source with high energy output and high conversion efficiency. The main research contents of this paper are the THz-wave radiation source based on stimulated polariton scattering and maximal atomic coherence between energy levels which are forbidden transition.The main contents and key innovative points are as follows:1. The dispersion relations of polariton in dual ion cubic crystal, dual ion uniaxial crystal and polyatomic crystal are analyzed. The three-wave interaction theory in the process of stimulated polariton scattering in LiNbO₃ crystal is investigated. The threshold express of TPO is deduced based on the theory of pulse laser resonant cavity and the expresses of THz-wave gain and absorption in gain medium. The tuning characteristics of quasi-phase-matched TPO are analyzed. An intracavity quasi-phase-matched TPO is proposed to ensure pump wave, Stokes wave and THz-wave collinearly propagate.2. The THz-wave is efficient generated from TPO with si-prism output coupler. The tuning range of THz-wave is 0.95-2.1 THz, and the average power is 580 nW with the energy conversion efficiency of 5.74×10^-7. The intensity of generated THz-wave from surface emitted TPO with two LiNbO₃ crystals is 1932 V when the pump energy is 80 mJ at 1.84 THz. The third order Stokes wave is generated as the pump intensity is high enough. The intensity of generated THz-wave from surface emitted TPO with one large volume LiNbO₃ crystal is 9.12μW with the energy conversion efficiency of 9.7×10^-6 when the pump energy is 94 mJ at 1.75 THz. The output power of THz-wave reaches leading level in China and advanced level in the world.3. The phase matching and gain characteristics of THz-wave generation in zinc-blende structure crystals are calculated based on the theory of stimulated polariton scattering. The calculated results provide a theoretical basis for using optical parametric method in zinc-blende structure crystals to generate THz-wave.4. The expressions of linear and nonlinear polarizability in the process of electromagnetically induced transparency are deduced. The linewidth and threshold expression of electromagnetically induced transparency in solid gain medium with a long-lived spin coherence is deduced based on the theory of electromagnetically induced transparency. The theory of THz-wave generation from maximal atomic coherence between energy levels which are forbidden transition in alexandrite is deduced based on the enhancement of nonlinear polarizability in the process of electromagnetically induced transparency.