| Terahertz(THz)wave lies between the microwave and infrared.Its frequency range is from 0.1 THz to 10 THz,its wavelength range is from 0.03 to 3 mm.It has comprehensive application prospects in the fields of non-destructive testing,imaging,environmental monitoring,communications and national security.The THz wave technology has become one of important technologies in the 21st century.The application and development of the THz technology are inseparable from the excellent THz sources.It has become an important task for researchers to obtain THz radiation sources with high output power,wide tuning range,and easy operation.There are two kinds of methods for THz generation:electronic methods and optical methods.THz wave parameter source is one of the important THz sources.The principle of THz wave parameter source is the stimulated polariton scattering.THz wave parameter sources have many advantages such as high peak power,continuous tuning,good temporal and spatial coherence,simple structure,room temperature operation,etc.The disadvantages are high pumping threshold and low conversion efficiency.In this thesis,the characteristics of injection-seeded THz parametric oscillators with a ring-cavity configuration are studied.We use one 5.0 mol%MgO doped LiNbO3 crystal as the nonlinear crystal.The surface-emitted configuration is used for the THz wave output in this experiment.The experimental results show that the injection-seeded THz parametric oscillator with a ring-cavity exhibits the benefits of lower pumping energy threshold,higher output energies and larger conversion efficiency.The main contents of this thesis are as follows:1.The ring cavity is constituted by three mirrors and the THz wave output surface where the pumping and Stokes beams are totally reflected.The experimental results show that the THz parametric oscillator with ring cavity has the advantage of inputting higher pumping energy.The input pumping energy is increased nearly 35%,compared to the THz parametric oscillator with double mirror linear cavity structure.Because the nonlinear crystal damage threshold is limited,higher input pump energy means that the output THz wave energy is higher.By adjusting the angle of the pump,we obtain the tunable THz wave output.The experimental results show that the THz wave output energy is significantly improved.2.By using Yb3+ gain fiber and a pair of fiber gratings,we get a continuous laser output at 1070.17 nm.The laser is injected into the THz parametric oscillator with the ring cavity,we study the output THz wave and Stokes pulse energies at different seed powers and different transmission mirrors.The experimental results show that higher output THz wave and Stokes pulse energies are obtained using the 0.20 nm linewidth injection seed THz parametric oscillator,and the maximum THz pulse energy is 1.16 ?J,the maximum Stokes pulse energy is 40.2 mJ.3.Using 1 kHz linewidth seed laser,the effect of narrow linewidth seed injection on the output energy is investigated.We get wider Stokes spectrum by directly injecting 1 kHz seed into the nonlinear crystal.In the experiment,the ring cavity is constituted by three mirrors and the THz wave output surface where the pumping and Stokes beams are totally reflected.The injection seeded THz parametric oscillator with a ring-cavity is a good method to increase the output THz and Stokes energies and reduce the threshold of the pump.When the output coupler is 20.1%,the threshold of the pump pulse energy is about 10 mJ.The maximum THz pulse energy output is 1.22 ?J.In another experiment,the ring cavity is constituted by two mirrors and the THz wave output surface where the pumping and Stokes beams are totally reflected.The experimental results show that this structure also exhibits the benefits of lower pumping energy threshold,higher output energies and larger conversion efficiency.The reasons for injection-seeded terahertz parametric oscillator performance improvement are analyzed. |
PDF Full Text Request