飞秒四波混频在超快超强激光技术中的应用(特邀)

Applications of Femtosecond Four-wave Mixing in Ultrafast and Ultraintense Laser Technology(Invited)

超快超强激光可以在实验室创造出超快时间、超强电场、超强磁场、超高温度及超高压力等多种极端物理实验条件,是当前拓展人类对物质世界认知最强有力的工具之一。在超快超强激光的发展过程中,飞秒四波混频过程在多个方面都发挥着非常重要的作用。本文介绍了飞秒四波混频过程在超快超强激光中近年来的一些进展和应用,系统总结了近年来利用级联四波混频、自衍射效应、瞬态光栅效应、四波光参量放大,以及交叉偏振波产生等飞秒四波混频过程,在宽带高对比度种子激光产生,新颖同心多色涡旋/径向偏振飞秒超快光源构建,“四阶相关仪”等脉冲对比度单发测量仪研制,以及脉冲形状宽度单发测量仪研制等方面的成果与进展。未来,飞秒四波混频过程还可拓展到太赫兹和极紫外等波段,继续为超快超强激光技术的发展做出重要贡献。

With the development of Chirped-pulse Amplification(CPA)and Optical Parametric Chirped-Pulse Amplification(OPCPA)techniques,ultrafast and ultraintense laser pulses can generate extreme physical conditions at lab such as ultrafast time,ultraintense electric field,ultrahigh magnetic field,ultrahigh temperature and ultrahigh pressure,which makes ultrafast and ultraintense laser pulses one of the most powerful tools to extend human's knowledge of the physical world.In the development of ultrafast and ultraintense lasers,femtosecond four-wave mixing process which is a third-order process and does not need anisotropic nonlinear crystals plays an important role in many aspects.Here,the development and application of femtosecond four-wave mixing processes on ultrafast and ultraintense laser pulses are discussed.Femtosecond pulses from Ultraviolet(UV)to Near-infrared(NIR)can be generated based on the Cascaded Four Wave Mixing(CFWM),which is of great significance in ultrafast spectroscopy,ultrafast microscopy and high temporal contrast seed pulse generation.By manipulating the spectral dispersion property,the polarization property,the spatial phase,or the crossing angle of the input beams,the CFWM signal with interesting properties can be generated.In this review article,the generation of spatially separated multicolored femtosecond sidebands from UV to NIR,the generation of highperformance seed pulses with high temporal contrast based on the CFWM or self diffraction process,and the generation of multicolor concentric annular ultrafast vector/vortex beams are demonstrated.Furthermore,based on the four wave mixing process,the generation of broadband ultrashort light pulses from narrowband seeds in transparent media can be realized.Broadband light pulses with a spectral width of hundreds of nanometers can be generated with narrowband light pulse seeds.Cross-correlator is the main method for high-dynamic single-shot temporal contrast measurement for the ultrafast and ultraintense laser pulses.Benefiting from excellent temporal domain filtering and high-energy signal generation of four-wave mixing,a single-shot Fourth-order Autocorrelation(FOAC)which consists of a four wave mixing process and a sum-frequency mixing process is developed.The signal of the self-diffraction process,or XPW process is used as the sampling pulse of the FOAC.And the stable devices with high dynamic range,wide time window,high temporal resolution,excellent measurement fidelity are combined in the proposed FOAC device,which can be helpful to investigate the temporal contrast property of high power laser pulses and realize better laser-matter interaction research.The Self-referenced Spectral Interferometry(SRSI)method with high time resolution of as high as 20 fs can also be used for the single shot temporal contrast measurement.However,the dynamic range is limited by the signal-to-noise ratio of the detector.To further improve the dynamic range,novel temporal contrast reduction techniques are proposed.The proofof-principle experiments applying single stage of pulse stretching,anti-saturated absorption,or optical Kerr effect successfully reduce the temporal contrast by approximately one order of magnitude.The dynamic range characterization capability of the SRSI method is improved by about one order of magnitude to 109.To characterize the temporal profile of femtosecond pulses,the SRSI method is also an analytical,sensitive,accurate,and fast method.We have developed the Self-diffraction Effect-based SRSI(SDSRSI)and Transient-grating(TG)Effect-based SRSI(TG-SRSI)for temporal profile characterization.The characterization of sub-10 fs pulse with a center wavelength of 1.8μm is demonstrated.On the basis of the TG effect,the SRSI and the Frequency-resolved Optical Gating(FROG)are combined together to further extend the measurement ability.Weak sub-nanojoule pulses from an oscillator are successfully characterized using a TG-SRSI device,and the optical setup of which is smaller than the palm of a hand.The compactness of the SISR device makes it convenient to use in many applications,including monitoring the pulse profile of laser systems as a sensor.In the future,the femtosecond four-wave mixing processes can be extended to the EUV and THz spectral ranges,which will extend the application range of ultrafast and ultraintense laser technology.