【摘要】 利用飞秒脉冲激光在晶体中进行光整流，是目前获取太赫兹波的重要技术方案。为突破单脉冲光整流太赫兹源在输出功率与波形调控方面的局限，本文提出并实现了基于双脉冲延迟泵浦的太赫兹波相干合成技术。选用高非线性系数的DSTMS(4-N,N-二甲基氨基-4’-N’-甲基-苯乙烯基吡啶-2,4,6-三甲基苯磺酸盐)有机晶体作为太赫兹产生介质，采用两束具有精确可控时间延迟的飞秒激光脉冲进行协同泵浦。通过电光采样方法，系统测量与分析了不同时间延迟下合成太赫兹脉冲的时域波形及频谱特性，实现了太赫兹波的高效相干合成与精准调控。通过改变泵浦脉冲间的延迟时间，可调控合成太赫兹波的时域波形（单周期、多周期脉冲）与频谱结构（特定频率分量的抑制或增强）。实验结果验证了双脉冲延迟泵浦相干合成技术在波形与频谱调控中的有效性，为研发高性能太赫兹源提供了新的技术路径。更多还原

【Abstract】 Objective Terahertz (THz) radiation covers the frequency range of 0.1??10 THz,bridging the electromagnetic gap between microwaves and infrared light,which is commonly known as the“THz gap.”It exhibits many unique properties,such as strong penetration ability,non-ionizing characteristics,and fingerprint spectral features.These properties give THz waves broad application potential in nondestructive testing,high-speed wireless communications,biomedical imaging,spectroscopic analysis,and national security inspection.High-power and waveform-programmable THz sources are particularly important,as they act as precise tools for exploring ultrafast dynamic processes in matter,including carrier transport,lattice vibrations,and molecular rotations,and also provide new insights for revealing novel physical and chemical phenomena.Ultrafast laser-pumped optical rectification in nonlinear crystals has been widely used for THz wave generation.However,traditional single-pulse pumping schemes suffer from persistent bottlenecks:the generated THz waveform is largely fixed,and the output energy is limited by the crystal damage threshold.These limitations restrict their applications in high-performance imaging,communications,and basic research.In this work,we present a coherent synthesis method based on dual-pulse time-delayed pumping in the organic crystal DSTMS (4-N,N-dimethylamino-4’-N’-methylstilbazolium 2,4,6-trimethylbenzenesulfonate) to generate waveform-programmable THz waves.Methods A dual-pulse time-delayed pumping system is constructed for terahertz generation.Two optical parametric amplifiers(OPAs) driven by a commercial Ti∶sapphire laser generate infrared laser pulses centered at 1.4μm and 1.7μm,respectively.Both pulses exhibit a duration of approximately 40 fs and an energy of 150μJ.The two laser beams are spatially combined and collinearly focused into a 0.4-mm-thick DSTMS crystal to generate THz waves through optical rectification.The inter-pulse delayΔt is adjusted by an optical delay line,which modulates the relative phase between the two generated THz pulses.The synthesized THz waveforms are characterized via electro-optic sampling using a 0.1-mm-thick GaP crystal.Time-domain waveforms and their Fourier-transform spectra are recorded over a delay range of several hundred femtoseconds.The THz pulse energy is measured with a pyroelectric detector to monitor its evolution as a function of the time delay.Results and Discussions The synthesized THz waveform is controlled by tuning the inter-pulse delay in the dual-pump scheme.At zero delay (Δt=0),the combined pump pulses generate a compressed single-cycle THz electric field.As the delay increases to±213 fs,the two THz pulses become temporally separated,and their constructive and destructive interference creates multi-cycle oscillatory waveforms.This transition from single-cycle to multi-cycle profiles demonstrates the programmability of the THz waveform.The THz pulse energy shows a non-monotonic dependence on the delay.Near zero delay,saturation of the pump fluence leads to a reduction in THz energy.As the pulses separate temporally,the energy increases steadily and approaches the linear superposition limit at large delays.Under dual-pulse pumping,the maximum synthesized THz energy reaches 1.6μJ,which is a significant improvement compared with the single-pulse case.Fourier-transform spectral analysis reveals selective modulation of the THz spectrum by the delay.Depending onΔt,specific frequency components are either enhanced or suppressed.This behavior follows a coherent superposition model described by■.Numerical simulations based on this model show excellent quantitative agreement with the measured spectra.These results confirm both the validity of the superposition model and the precise delay control implemented in the experiment.Conclusions We demonstrate a coherent synthesis strategy for generating waveform-programmable THz pulses via dual-pulse time-delayed pumping in the organic crystal DSTMS.By precisely controlling the inter-pulse delayΔt between two collinearly combined pump laser pulses,we achieve active manipulation of the synthesized THz waveform.This programmability addresses a key limitation of conventional single-pulse pumping schemes,where the THz waveform is inherently fixed.Furthermore,the dual-pulse approach effectively overcomes the energy constraints imposed by pump fluence saturation.The selective enhancement and suppression of specific frequency components are quantitatively described by a coherent superposition model.The excellent agreement between experimental measurements and numerical simulations confirms both the validity of this model and the high precision of the delay control.These results establish dual-pulse time-delayed pumping as a robust and flexible method for tailoring THz waveforms,offering new opportunities for advanced applications in ultrafast spectroscopy,nonlinear optics,and THz-driven dynamic control of matter.更多还原