P. Bowlan, R. Trebino, H. Valtna-Lukner, M. Lohmus, P. Piksarv, P. Saari
Using SEA TADPOLE with micrometer-range spatial and femtosecond-range temporal resolution, we report the first direct spatiotemporal measurements of ultrashort Bessel-X pulses. We demonstrate their propagation invariance and superluminal velocity and verify our results with simulations
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We measure the detailed spatiotemporal profiles of femtosecond laser pulses in the infrared wavelength range λ=2.5-11μm, and the absolute nonlinear response of major air constituents (N2, O2, and Ar) over this range. The spatiotemporal measurements reveal wavelength-dependent pulse front tilt and temporal stretching in the infrared pulses.
By using a reductive perturbation method, we derive from Maxwell-Bloch equations a cubic generalized Kadomtsev-Petviashvili equation for ultrashort spatiotemporal optical pulse propagation in cubic (Kerr-like) media without the use of the slowly varying envelope approximation. We calculate the collapse threshold for the propagation of few-cycle spatiotemporal pulses described by the generic cubic generalized Kadomtsev-Petviashvili equation by a direct numerical method and compare it to analytic results based on a rigorous virial theorem. Besides, typical evolution of the spectrum (integrated o…
Generation of few-cycle optical vortex pulses is challenging due to the large spectral bandwidths, as most vortex generation techniques are designed for monochromatic light. In this work, we use a spiral phase plate to generate few-cycle optical vortices from an ultrafast titanium:sapphire oscillator, and characterize them in the spatiotemporal domain using a recently introduced technique based on spatially resolved Fourier transform spectrometry. The performance of this simple approach to the generation of optical vortices is analyzed from a wavelength dependent perspective, as well as in the…
We investigate the dynamics of spatiotemporal optical waves with one transverse dimension that are obtained as the intersections of the dispersion cone with a plane. We show that, by appropriate spectral excitations, the three different types of conic sections (elliptic, parabolic, and hyperbolic) can lead to optical waves of the Bessel, Airy, and modified Bessel type, respectively. We find closed form solutions that accurately describe the wave dynamics and unveil their fundamental properties.
By using a powerful reductive perturbation technique, or a multiscale analysis, a generic Kadomtsev-Petviashvili evolution equation governing the propagation of femtosecond spatiotemporal optical solitons in quadratic nonlinear media beyond the slowly varying envelope approximation is put forward. Direct numerical simulations show the formation, from adequately chosen few-cycle input pulses, of both stable line solitons (in the case of a quadratic medium with normal dispersion) and of stable lumps (for a quadratic medium with anomalous dispersion). Besides, a typical example of the decay of th…
We propose a new experimental technique, which allows for a complete characterization of ultrashort optical pulses both in space and in time. Combining the well-known Frequency-Resolved-Optical-Gating technique for the retrieval of the temporal profile of the pulse with a measurement of the near-field made with an Hartmann-Shack sensor, we are able to retrieve the spatiotemporal amplitude and phase profile of a Bessel-X pulse. By following the pulse evolution along the propagation direction we highlight the superluminal propagation of the pulse peak.
We develop a spatiotemporal mode decomposition technique to study the mode power distribution of ultrashort pulses emerging from long spans of graded-index multimode fiber, for different input laser conditions. We find that beam mode power content in the dispersive pulse propagation regime can be described by the Bose-Einstein law, as a result of the process of power diffusion from linear and nonlinear mode coupling among nondegenerate mode groups. In the soliton regime, the output mode power distribution approaches the Rayleigh-Jeans law
By using a reductive perturbation technique applied to a two-level model, this study puts forward a generic two-dimensional sine-Gordon evolution equation governing the propagation of femtosecond spatiotemporal optical solitons in Kerr media beyond the slowly varying envelope approximation. Direct numerical simulations show that, in contrast to the long-wave approximation, no collapse occurs, and that robust (2+1)-dimensional ultrashort light bullets may form from adequately chosen few-cycle input spatiotemporal wave forms. In contrast to the case of quadratic nonlinearity, the light bullets o…
Ultra-high intensity femtosecond lasers at focus are now routinely used for relativistic motion of charged particles with peak intensities over 10^18W/cm^2. Such high-field experiments are very sensitive to the value of the peak intensity. Therefore, precise knowledge of the pulse intensity is a key prerequisite for the correct interpretation of experimental data. Accurate measurement of energy, spectral and spatial profiles being well established, peak intensity evaluation then only requires the determination of the spatiotemporal Strehl ratio. Here I propose a new method based on a simple an…
We present a technique for the single-shot measurement of the space- and time-resolved spatiotemporal amplitude and phase of an ultrashort laser pulse. The method, transient-grating single-shot supercontinuum spectral interferometry (TG- SSSI), is demonstrated by the space-time imaging of short pulses carrying spatiotemporal optical vortices (STOVs). TG-SSSI is well-suited for characterizing ultrashort laser pulses that contain singularities associated with spin/orbital angular momentum or polarization.
We shape fs optical pulses and deliver them in a single spatial mode to the input of a multimode fiber. The pulse is shaped in time such that at the output of the multimode fiber an ultrashort pulse appears at a predefined focus. Our result shows how to raster scan an ultrashort pulse at the output of a stiff piece of square-core step-index multimode fiber and in this way the potential for making a nonlinear fluorescent image of the scene behind the fiber, while the connection to the multimode fiber can be established via a thin and flexible single-mode fiber. The experimental results match ou…
Spatiotemporal Control of Ultrafast Pulses in Multimode Optical Fibers
研究通过定制超短光脉冲的时空结构，克服多模光纤中色散和模式色散的限制，合成具有预定义动力学的光态，推动多模光通信、成像及超快光物质相互作用等激光技术发展。
Single-scan, dual-functional interferometer for fast spatiotemporal characterization of few-cycle pulses
针对传统超短脉冲时空表征需额外测量、系统复杂的问题，提出集成干涉式FROG与径向剪切迈克尔逊干涉仪的双功能装置，单次扫描即可同时获取两类数据，实现少周期脉冲快速三维重建。
Femtosecond laser micromachining provides high precision and less thermal diffusion in surface structuring as a result of the ultrashort temporal duration and ultrahigh peak intensity of the femtosecond laser pulses. To increase the throughput of surface patterning, the focal spot size can be expanded with loose focusing, which, however, could lead to nonlinear self-focusing of the pulses when the pulses propagate in air. We solve the problem by use of spatiotemporally focused femtosecond laser pulses for ablation of metal surfaces, which gives rise to improved surface quality as compared with…
Effects of Random Birefringence in Multimode Fibers on Nonlinear Ultrashort Pulse Propagation
本文利用修正的广义多模非线性薛定谔方程研究随机双折射对超短脉冲传输的影响，揭示其通常削弱非线性但与孤子自频移关系复杂，并发现高功率下光束自清洁仍可保持。
We report broadband characterization of the propagation of light through a multiply scattering medium by means of its Multi-Spectral Transmission Matrix. Using a single spatial light modulator, our approach enables the full control of both spatial and spectral properties of an ultrashort pulse transmitted through the medium. We demonstrate spatiotemporal focusing of the pulse at any arbitrary position and time with any desired spectral shape. Our approach opens new perspectives for fundamental studies of light-matter interaction in disordered media, and has potential applications in sensing, c…
Ultrafast spatiotemporal chiroptical response of dielectric and plasmonic nanospheres
该研究从理论上探究超短脉冲激发下等离激元与电介质纳米球的近场光学手性时空演化，揭示两类谐振器的手性响应差异及机制，验证矢量光束的调控能力，为手性光-物质相互作用的时空调控提供新可能。
We report on the usage of ultrashort laser pulses in form of aberration-corrected Bessel-like beams for laser cutting of glass with bevels. Our approach foresees to incline the material's entrance surface with respect to the processing optics. The detailed analysis of phase distortions caused by the beam transition through the tilted glass surface allows to pre-compensate occurring aberrations using digital holography. We verify theoretical considerations by means of pump-probe microscopy and present high-quality edges in non-strengthened silicate glass.
Spatiotemporal Hologram
针对时空光难以同时调控振幅与相位的问题，提出一种通用时空全息方法，可任意定制多种时空波包并服务于光-物质相互作用研究。
Recently, spatiotemporal optical vortex pulses carrying a purely transverse intrinsic orbital angular momentum were generated experimentally [{\it Optica} {\bf 6}, 1547 (2019); {\it Nat. Photon.} {\bf 14}, 350 (2020)]. However, an accurate theoretical analysis of such states and their angular-momentum properties remains elusive. Here we provide such analysis, including scalar and vector spatiotemporal Bessel-type solutions as well as descrption of their propagational, polarization, and angular-momentum properties. Most importantly, we calculate both local densities and integral values of the s…
Diffraction-free Bessel beams have attracted major interest because of their stability even in regimes of nonlinear propagation and filamentation. However, Kerr nonlinear couplings are known to induce significant longitudinal intensity modulation, detrimental to the generation of uniform plasma or for applications in the processing of transparent materials. These nonlinear instabilities arise from the generation of new spatio-spectral components through an initial stage of continuous spectral broadening followed by four wave mixing. In this paper, we investigate analytically and numerically th…
Transverse orbital angular momentum imparted upon focusing spatio-temporally coupled ultrashort pulses
本文研究聚焦系统赋予时空耦合超短脉冲横向轨道角动量的机制，给出随焦距和协方差变化的解析表达式，并提供了适用于任意传播距离的闭合形式解，涵盖椭圆ST涡旋与旋转脉冲等场型。
Broadband amplification of light through adiabatic spatiotemporal modulation
本文提出利用绝热时空调制图案和双各向异性非互易介质的时间调制，无需亚周期时间响应即可实现光的宽带放大，为产生高能量超短光脉冲开辟了新途径。
We propose a novel method to reconstruct the spatio-temporal amplitude and phase of the electric field of ultrashort laser pulses using spatially-resolved spectral interferometry. This method is based on a fiber-optic coupler interferometer that has certain advantages in comparison with standard interferometer systems, such as it being alignment-free and selection of the reference beam at a single point. Our technique, which we refer to as STARFISH, offers compactness and simplicity. We report its application to the experimental characterization of chirped pulses and to spatio-temporal reconst…
Perfect Spatiotemporal Optical Vortices
针对时空光学涡旋空间时间维度受拓扑荷限制的问题，提出完美时空光学涡旋，其直径与拓扑荷无关，并实现涡旋晶格的灵活操控。
A photon is the single excitation of a particular spatiotemporal mode of the electromagnetic field. A precise knowledge of the mode structure is therefore essential for its processing and detection, as well as for applying generic quantum light states to novel technologies. Here we demonstrate an adaptive scheme for reconstructing the arbitrary amplitude and phase spectro-temporal profile of an ultrashort single-photon pulse. The method combines techniques from the fields of ultrafast coherent control and quantum optics to map the mode of a fragile quantum state onto that of an intense coheren…
In any form of wave propagation, strong spatiotemporal coupling appears when non-elementary, three-dimensional wave-packets are composed by superimposing pure plane waves, or spontaneously generated by light-matter interaction and nonlinear processes. Ultrashort pulses with orbital angular momentum (OAM), or ultrashort vortices, furnish a critical paradigm in which the analysis of the spatiotemporal coupling in the form of temporal-OAM coupling can be carried out accurately by analytical tools. By generalizing and unifying previously reported results, we show that universal and spatially heter…
Enhanced spatiotemporal optical vortices and vortex chains from Hermite-Gauss modes with a tilted pulse front
本文提出聚焦带脉冲前倾斜的脉冲 Hermite-Gaussian 光束以产生椭圆形 STOV 或涡旋链，利用空间啁啾增强横向轨道角动量并显著增大纵向场，从而简化 STOV 产生方案。
Perfect spatiotemporal optical vortex driven high harmonic generation
本文理论研究了完美时空光涡旋驱动的高次谐波产生，证明横向轨道角动量守恒，并利用近场瓣状结构及远场发散特性，为在极紫外波段产生高拓扑荷贝塞尔-高斯时空涡旋光束提供了新途径。
Controllable perfect spatiotemporal optical vortices
针对常规时空光学涡旋强度分布半径随拓扑荷变化的局限，提出完美时空光学涡旋概念，其强度几乎不受拓扑荷影响，可通过时空傅里叶变换生成且模式能经方位角相位调制自由调控，实验验证了该波包的生成，拓展了相关研究与应用场景。
Spatiotemporal control of two-color terahertz generation
该研究利用时空结构化双色激光脉冲的可编程速度强度峰，实现对THz辐射发射角、焦斑与光谱的控制，并获得高度可聚焦的轴上辐射。
We present a study of the propagation of three-dimensional (3D) bipolar electromagnetic ultrashort pulses in an inhomogeneous array of semiconductor carbon nanotubes (CNTs) in the presence of a control high-frequency (HF) electric field. The inhomogeneity is present in the form of a layer with an increased concentration of conduction electrons, which acts as a barrier for the propagation of ultrashort electromagnetic pulses through the CNT array. The dynamics of the pulse is described by a nonlinear equation for the vector potential of the electromagnetic field (it takes the form of a 3D gener…
The performance of fiber mode-locked lasers is limited due to the high nonlinearity induced by the spatial confinement of the single-mode fiber core. To massively increase the pulse energy of the femtosecond pulses, amplification is obtained outside the oscillator. Recently, spatiotemporal mode-locking has been proposed as a new path to fiber lasers. However, the beam quality was either highly multimode and/or with low pulse energy. Here we present an approach to reach high energy per pulse directly in the mode-locked multimode fiber oscillator with a near single-mode output beam. Our approach…
Ultra-Short flying-focus
本文提出通过径向依赖的频谱啁啾补偿色散时间不匹配，实现超短脉冲在扩展焦区内的飞行焦点速度控制，拓展了 achromatic flying-focus 技术在激光-等离子体相互作用和高场非线性光学中的应用。
Photonic time stretch fieldoscopy: single-shot electric field detection at near-petahertz bandwidth
该研究提出光子时间拉伸场成像技术，实现近拍赫兹带宽下的单次电场检测，提升超快光谱显微镜的性能。
We present a novel approach for tailoring the laser induced surface topography upon femtosecond-fs pulsed laser irradiation. The method employs spatially controlled double fs laser pulses to actively regulate the hydrodynamic microfluidic motion of the melted layer that gives rise to the structures formation. The pulse train used, in particular, consists of a previously unexplored spatiotemporal intensity combination including one pulse with Gaussian and another with periodically modulated intensity distribution created by Direct Laser Interference Patterning (DLIP). The interpulse delay is ap…
The use of structured ultrashort pulses with coupled spatiotemporal properties is emerging as a key tool for ultrafast manipulation. Ultrafast vector beams are opening exciting opportunities in different fields such as microscopy, time-resolved imaging, nonlinear optics, particle acceleration or attosecond science. Here, we implement a technique for the full characterization of structured time-dependent polarization light waveforms with spatiotemporal resolution, using a compact twofold spectral interferometer, based on in-line bulk interferometry and fibre-optic coupler assisted interferometr…
Temporally and Longitudinally Tailored Dynamic Space-Time Wave Packets
本研究提出并验证了一类可在纵向传播路径任意预设距离处实现时空调控演化的动态时空波包，通过二维频谱合成实现多光自由度独立调控，拓展了时空动力学研究维度并具备多领域应用潜力。
It was demonstrated during the past decade that ultrashort intense laser pulse tightly focused deep inside a transparent dielectric generates the energy density in excess of several MJ/cm3. Such energy concentration with extremely high heating and quenching rates leads to unusual solid-plasma-solid transformation paths overcoming kinetic barriers to formation of previously unknown high-pressure material phases, which are preserved in the surrounding pristine crystal. These results were obtained with the pulse of Gaussian shape in space and in time. Recently it was shown that the Bessel-shaped …
Light carrying spatiotemporal orbital angular momentum (ST-OAM) makes possible new types of optical vortices arising from transverse OAM. ST-OAM pulses exhibit novel properties during propagation, transmission, refraction, diffraction, and nonlinear conversion, attracting growing experimental and theoretical interest and studies. However, one major challenge is the lack of a simple and straightforward method for characterizing ultrafast ST-OAM pulses. Using spatially resolved spectral interferometry, we demonstrate a simple, stationary, single-frame method to quantitatively characterize ultras…
Influence of Inter-Pulse Delay and Geometric Constraints on Damage and Optical Characteristics in thin Metal Targets Irradiated by Double Ultrashort Laser Pulses
本文研究双超短激光脉冲对薄金属靶损伤和光学特性的影响，通过理论分析探讨脉冲间隔和几何约束对激光诱导损伤阈值的影响，为激光微加工和纳米制造提供理论基础。
Bridging the gap between ultrafast optics and resonant photonics via omni-resonance
本文提出“全共振”方法，通过引入角色散使超快脉冲整个带宽耦合到单个腔共振，实现腔内峰值强度提升，为非线性光学效应的宽带共振增强铺平道路。
Visible optical vortices measured with bulk lateral shearing interferometry
研究利用结构化波片、二次谐波产生晶体等，通过体横向剪切干涉测量法产生并表征可见光学涡旋，验证了可见范围内脉冲产生，证明同一装置可用于不同光谱区域脉冲光束，对技术未来应用有重要意义。
Controllable ultrabroadband supercontinuum during twocolor femtosecond laser filamentation in high pressure gases
本研究通过实验揭示高压气体中双色飞秒激光成丝的超连续谱动态调控机制，发现多丝化导致复杂光谱依赖及原子与分子气体差异，为可控超短脉冲产生提供新途径。
Spatiotemporal THz emission from radial and longitudinal wakefields by copropagating chirped lasers in magnetized rippled plasma
研究通过FBPIC模拟探讨了共传播啁啾激光脉冲在磁化不规则等离子体中激发径向和纵向射频场的时空演化及其在太赫兹辐射生成中的作用，发现啁啾、脉冲持续时间和等离子体密度显著影响射频场振幅和相干性。
Ultrafast imaging is essential in physics and chemistry to investigate the femtosecond dynamics of nonuniform samples or of phenomena with strong spatial variations. It relies on observing the phenomena induced by an ultrashort laser pump pulse using an ultrashort probe pulse at a later time. Recent years have seen the emergence of very successful ultrafast imaging techniques of single non-reproducible events with extremely high frame rate, based on wavelength or spatial frequency encoding. However, further progress in ultrafast imaging towards high spatial resolution is hampered by the lack o…
Field enhancement of intense laser pulses in a subwavelength plasma aperture
本研究通过三维粒子模拟证实强激光脉冲在亚波长等离子体孔径中可实现非共振的显著场增强，揭示其能量集中源于入射场与背向散射纵向场的干涉，为极端强度下的等离子体光学器件应用提供了可能。
Dynamics of relativistic vortex electrons in external laser fields
本研究利用Volkov-Bessel波函数理论框架，系统研究了相对论涡旋电子与线偏振、圆偏振及其叠加激光脉冲正面碰撞的动力学，发现束中心遵循经典轨迹且保持横向结构，CP导致旋转、LP导致横向位移，叠加产生螺旋图案，展示了激光模式对涡旋电子束的多功能控制潜力。
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