Femtosecond Optical Parametric Oscillator And Its Application In Terahertz Generation

The femtosecond optical parameter oscillator(OPO)is a broadband tunable femtosecond laser,which is developed alone with the development of femtosecond laser technology.A high average power,high peak power and high repetition rate of bump source is required to achieve the high average power of the femtosecond OPO,while the new generation of photonic crystal fiber lasers and amplifiers can qualify the requirement.The ultra-wide cover range and the broadband tunable wavelength make the femtosecond OPO promising in various applications,including ultrafast biology,ultrafast chemistry,laser spectroscopy,optical communication and other fields.Among of them,the one of the hot research fields is in the application of femtosecond OPO to the ultrafast terahertz generation.In this thesis,basing the preliminary work in the laboratory on the photonic crystal fiber femtosecond laser,OPO and the generation of THz,the main work is summarized as follow:1.A brief introduction is devoted to the development and application of femtosecond OPO,the research advances on ultrafast THz technology,the basic theory of nonlinear optics and the foundation of OPO including the frequency tunability and threshold property.The basic principle of the terahertz generation by the difference frequency,the birefringence-phase-match and the quasi-phase-match technology are also illuminated.2.The configure and parameters of the resonance cavity of the femtosecond OPO are designed based on the bump source used.The corresponding near-IR linear-cavity OPO system with a PPLN as the nonlinear crystal pumped by the PCF femtosecond amplification system is developed.The experimental result in a tenability of the spectral width between 1380 nm and 1700 nm is demonstrated,by simply tuning the period or temperature of the crystal.Furthermore,a new system with separately tunable double near-IR OPOs is constructed.The double-OPO source can extend the spectral bandwidth tunability nearly two times than that by a single cannel OPO,and make it to be used to generate broadband tunable THz waves by difference frequency.3.The experimental investigation of THz generation using single cannel near-IR femtosecond OPO is presented.Basing on optical rectification method,the THz generation system with an organic nonlinear crystal of DAST as THz emitter and pumped by the single cannel near-IR OPO system is manufactured.The relationship between the power of THz wave and the wavelength of pump OPO is obtained by measuring the output powers of the THz generated under different OPO signal wavelength using a Golay-cell.A highest THz power of 134 nW is generated by a 400?m DAST under the pump conditions of the pulse duration of 285 fs,the average power of 200 mW and the centered wavelength at 1450 nm,which the OR conversion efficiency is higher sufficiently than that of GaP crystal under the same condition.4.The THz wave generation with a DAST by difference frequency is tested,thanks to the separately tunable double near-IR OPO system.