Antoine Monmayrant, Béatrice Chatel, Bertrand Girard
We have implemented a new approach for measuring the time-dependent intensity and phase of ultrashort optical pulses. It is based on the interaction between shaped pulses and atoms, leading to coherent transients.
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We report on experimental observations of formation and evolution of transient plasma produced in fused silica glass with spatiotemporally focused (STF) femtosecond laser pulses using a pump-probe shadow imaging technique. Surprisingly, the observation shows that the track of the plasma is significantly curved, which is attributed to an asymmetric density distribution of the transient plasma produced in the focal volume caused by the pulse front tilt of the STF laser field.
The self-referenced spectral interferometry (SRSI) technique, which is usually used for microjoule-level femtosecond pulses characterization, is improved to characterize weak femtosecond pulses with nanojoule based on the transient-grating effect. Both femtosecond pulses from an amplifier with 3 nJ per pulse at 1 kHz repetition rates and femtosecond pulses from an oscillator with less than 0.5 nJ per pulse at 84 MHz repetition rates are successfully characterized. Furthermore, through a special design, the optical setup of the device is even smaller than a palm which will makes it simple and c…
Propagation of ultrashort optical pulses in a dense resonant medium is considered in the semiclassical limit. In our analysis, we place emphasis on several main points. First, we study transformations of spectra in the process of pulse propagation and interactions with another pulse. The second point involves the transient processes (including pulse compression) connected with self-induced transparency soliton formation inside the medium. Finally, the third aspect is the study of collisions of co- and counter-propagating pulses in the medium. In the last case, the investigation of symmetric an…
Nonlinear Generation, Compression and Spatio-Temporal Analysis of GV/cm-Class Femtosecond Mid-Infrared Transients
本研究利用3 kHz薄盘再生放大器泵浦二阶非线性混频，结合自相位调制突破参量下转换的效率-带宽限制，产生场强超330 MV/cm的45 THz飞秒中红外瞬态，并在亚周期尺度研究孤子自压缩与超连续谱。
Infrared femtosecond laser pulses are important tools both in strong-field physics, driving X-ray high-harmonic generation, and as the basis for widely tuneable, if inefficient, ultrafast sources in the visible and ultraviolet. Although anomalous material dispersion simplifies compression to few-cycle pulses, attosecond pulses in the infrared have remained out of reach. We demonstrate soliton self-compression of 1800 nm laser pulses in hollow capillary fibers to sub-cycle envelope duration (2 fs) with 27 GW peak power, corresponding to attosecond field transients. In the same system, we genera…
Femtosecond spectroscopy is an important tool for tracking rapid photoinduced processes in a variety of materials. To spatially map the processes in a sample would substantially expand the capabilities of the method. This is, however, difficult to achieve due to the necessity to use low-noise detection and to maintain feasible data acquisition time. Here we demonstrate realization of an imaging pump-probe setup, featuring sub-100 fs temporal resolution, by a straightforward modification of a standard pump-probe technique, using a randomly structured probe beam. The structured beam, made by a d…
We demonstrate a tilted pulse-front transient grating technique that allows to optimally utilize time-resolution as well as transient grating line density while probing under grazing incidence as typically done in extreme ultraviolet (EUV) or soft x-ray (SXR) experiments. Our optical setup adapts the pulse front tilt of the two pulses that create the transient grating to the relative tilt grazing incident pulse. We demonstrate the technique using all 800 nm femtosecond laser pulses for transient grating generation on a vanadium dioxide film. We probe that grating via diffraction of a third 800…
Coherent control is an optical technique to manipulate quantum states of matter. The coherent control of 40-THz optical phonons in diamond was demonstrated by using a pair of sub-10-fs optical pulses. The optical phonons were detected via transient transmittance using a pump and probe protocol. The optical and phonon interferences were observed in the transient transmittance change and its behavior was well reproduced by quantum mechanical calculations with a simple model which consists of two electronic levels and shifted harmonic oscillators.
Versatile Femtosecond Laser Synchronization for Multiple-Timescale Transient IR Spectroscopy
本文提出基于可编程电子硬件的多种飞秒激光同步方法，可在单次瞬态吸收实验中覆盖从皮秒到秒级时间尺度，无需移动延迟台，并成功用于金属羰基配合物和细菌视紫红质的瞬态红外测量。
X-ray Free-Electron Lasers (XFELs) deliver X-ray pulses with a coherent flux that is approximately eight orders of magnitude greater than that available from a modern third generation synchrotron source. The power density in an XFEL pulse may be so high that it can modify the electronic properties of a sample on a femtosecond timescale. Exploration of the interaction of intense coherent X-ray pulses and matter is of both intrinsic scientific interest, and of critical importance to the interpretation of experiments that probe the structures of materials using high-brightness femtosecond XFEL pu…
We describe the development of a broadband magneto-optical spectrometer with femtosecond temporal resolution. The absorption spectrometer is based on a white-light supercontinuum (ca. 320 - 750 nm) using shot-to-shot temporal and spectral referencing at 1 kHz. Static and transient absorption spectra using circularly polarised light are collected in a magnetic field. The difference spectra with respect to the external field direction give the static and transient magneto-optical Faraday rotation (magnetic optical rotary dispersion) and ellipticity (magnetic circular dichroism) spectra. An achro…
Oscillator-driven broadband femtosecond transient microspectroscopy with supercontinuum probes generated in a photonic crystal fiber
本文开发了一种振荡器驱动的宽带飞秒瞬态显微光谱系统，采用光子晶体光纤产生超连续谱探针，可实现高灵敏度、高时空分辨率的显微光谱测量，成功解析了低维材料的局域超快载流子动力学。
Few-femtosecond phase-sensitive detection of infrared electric fields with a third-order nonlinearity
提出利用三阶非线性与多周期脉冲直接探测中红外电场瞬态，实现相位敏感测量，并提取介电函数实部，为时间分辨光谱提供新途径。
We present a rapid-scan, time-domain terahertz spectrometer employing femtosecond Er:fiber technology and an acousto-optic delay with attosecond precision, enabling scanning of terahertz transients over a 12.4 ps time window at a waveform refresh rate of 36 kHz, and a signal-to-noise ratio of $1.7 \times 10^5/\sqrt{\rm Hz}$. Our approach enables real-time monitoring of dynamic THz processes at unprecedented speeds, which we demonstrate through rapid 2D thickness mapping of a spinning teflon disc at a precision of $10\,\rm nm/\sqrt{\rm Hz}$. The compact, all-optical design ensures alignment-fre…
We report an experiment to measure the femtosecond electric field of the signal emitted from an optical third-order nonlinear interaction in carbon dioxide molecules. Using degenerate four-wave mixing with femtosecond near infrared laser pulses in combination with the ultra-weak femtosecond pulse measurement technique of TADPOLE, we measure the nonlinear signal electric field in the time domain at different time delays between the interacting pulses. The chirp extracted from the temporal phase of the emitted nonlinear signal is found to sensitively depend on the electronic and rotational contr…
We demonstrate a novel method to measure the temporal evolution of electric fields with optical frequencies. Our technique is based on the detection of transient currents in air plasma. These directional currents result from sub-cycle ionization of air with a short pump pulse, and the steering of the released electrons with the pulse to be sampled. We assess the validity of our approach by comparing it with different state-of-the-art laser-pulse characterization techniques. Notably, our method works in ambient air and facilitates a direct measurement of the field waveform, which can be viewed …
Energy carrier evolution is crucial for material performance. Ultrafast microscopy has been widely applied to visualize the spatiotemporal evolution of energy carriers. However, direct imaging of small amounts of energy carriers on nanoscale remains difficult due to extremely weak transient signals. Here we present a method for ultrasensitive and high-throughput imaging of energy carrier evolution in space and time. This method combines femtosecond pump-probe techniques with interferometric scattering microscopy (iSCAT), named Femto-iSCAT. The interferometric principle and unique spatially-mod…
Transient Gas-Dynamics Filamentation of High-PowerFemtosecond Laser Pulse in Compressed Argon
研究高强度飞秒激光脉冲在压缩氩气中暂态气体动力学丝状结构的光谱特性及空间结构，揭示了压力冲击降条件下强喷流和涡旋气体湍流的形成及其对光脉冲谱宽的影响，提出了通过丝状结构控制超连续辐射光谱的有效方法。
We demonstrate that Freeman resonances have a strong impact on the nonlinear optical response in femtosecond filaments. These resonances decrease the transient refractive index within a narrow intensity window and strongly affect the filamentation dynamics. In particular, we demonstrate that the peak intensity of the filament can be clamped at these resonances, hinting at the existence of new regimes of filamentation with electron densities considerably lower than predicted by the standard model. This sheds a new light on the phenomenon of filamentary intensity clamping and the plasmaless fila…
We have measured the frequency of the $6s^2S_{1/2} - 5d^2D_{3/2}$ electric-quadrupole transition of $^{171}$Yb$^+$ with a relative uncertainty of $1\times 10^{-14}$, $ν_{Yb}$ = 688 358 979 309 312 Hz $\pm$ 6 Hz. A femtosecond frequency comb generator was used to phase-coherently link the optical frequency derived from a single trapped ion to a cesium fountain controlled hydrogen maser. This measurement is one of the most accurate measurements of optical frequencies ever reported, and it represents a contribution to the development of optical clocks based on an $^{171}$Yb$^+$ ion standard.
We propose a new concept for generation of ultrashort pulses based on transient plasmonic resonance in nanoparticle composites. Photoionization and free-carriers plasma change the susceptibility of nanoparticles on a few-femtosecond scale. This results in a narrow time window during the pump pulse duration when the system is in plasmonic resonance, accompanied by a short burst of the local field. During this process, frequency-tunable few-fs pulses are generated. We elucidate the details of the above mechanism, and investigate the influences of different contributing processes.
We report a novel scheme to generate laser-induced, ultrafast, intense (Tesla scale), spatially isolated, magnetic fields. Three-dimensional particle-in-cell simulations show that a femtosecond azimuthally-polarized infrared vector beam, aimed to a conducting circular aperture, produces an intense axially polarized tip-shaped femtosecond magnetic field, extending over micrometer distances and being isolated from the electric field. Our results are backed-up by an analytic model, demonstrating the underlying physics and guiding for optimal parameters. In particular, we find the conditions under…
Dissipation of electromagnetic energy through absorption is a fundamental process that underpins phenomena ranging from photovoltaics to photography, analytical spectroscopy, photosynthesis, and human vision. Absorption is also a dynamic process that depends on the duration of the optical illumination. Here we report on the resonant plasmonic absorption of a nanostructured metamaterial and the non-resonant absorption of an unstructured gold film at different optical pulse durations. By examining the absorption in travelling and standing waves, we observe a plasmonic relaxation time of 11 fs as…
High-power femtosecond mid-IR source with tunable center frequency and chirp
本研究实现了一种中心频率在4至30 THz可调、单脉冲内扫频达20%的啁啾中红外高功率激光源，通过差频产生过程生成2 ps脉冲，峰值电场达1.5 MV/cm，为避免介电击穿并高效驱动强非简谐振动模式提供了新途径。
Ultra-broadband transient absorption down to 200 nm enabled by soliton dynamics in gas-filled hollow capillary fibers
该研究利用充气空心毛细管光纤的孤子动力学，实现了覆盖200-800 nm的超宽带飞秒瞬态吸收，分辨率达9 μOD，成功解析Fe(II)配合物的DUV超快自旋交叉动力学，为研究DUV波段光物理化学动力学提供了新方法。
For fused silica irradiated by near-100-fs, 795-nm laser pulses with fluence approaching the damage threshold, the transient transmission spectroscopy based on a wavelength-degenerate pump-probe technique clearly presents two dynamic processes corresponding to the instantaneous effects of laser optical field and the delayed effects of free electron dynamics, respectively. The reversible, instantaneous process originates in third-order nonlinear optical responses (in particular the optical Kerr effect) ascribed to virtual optical-field ionization (VOFI) that significantly contributes to the non…
Coherent radiation with frequencies ranging from 0.3 to 30 THz has recently become accessible by femtosecond laser technology. Terahertz (THz) waves have already found many applications in spectroscopy and imaging, and they can be manipulated using static optical elements such as lenses, polarizers, and filters. However, ultrafast modulation of THz radiation is required as well, for instance in short-range wireless communication or for preparing shaped THz transients for coherent control of numerous material excitations. Here, we demonstrate an all-optically created transient metamaterial that…
Time-interval Measurement with Linear Optical Sampling at the Femtosecond Level
本文提出基于光频梳线性光学采样的电信号时间间隔测量方法，实现单次82 fs、百次平均3.05 fs精度，较传统电学方法提升三个数量级。
This paper reports the observation of ultra-superluminal pulse propagation in GaAs/AlGaAs multiple contact heterostuctures in a superradiant emission regime, and shows definitively that it is a different class of emission from conventional spontaneous or stimulated emission. It is shown that coherent population gratings induced in the semiconductor medium under strong electrical pumping have great impact in causing a decrease of the group refractive index in the range of 5-40%. This decrease is much greater than that which would be observed due to conventional carrier depletion or chirp mechan…
Laser induced periodic surface structures (LIPSS) are formed by multiple irradiation of femtosecond laser on a silicon target. In this paper, we focus and discuss the surface plasmon polariton mechanism by an analysis of transient phase-matching conditions in Si on the basis of a single pulse experiment and numerical simulations. Two regimes of ripple formation mechanisms at low number of shots are identified and detailed. Correlation of numerical and experimental results is good.
We present the experimental realization of transverse mode conversion in an optical fiber via an optically induced long-period grating. The transient gratings are generated by femtosecond laser pulses, exploiting the Kerr effect to translate intensity patterns emerging from multimode interference into a spatial refractive index modulation. Since these modulations exist only while the pump beam is present, they can be used for optical switching of transverse modes. As only a localized part of the grating was written at a time and the probe beam was co-propagating with the pump beam the required…
Super-resolution femtosecond electron diffraction reveals electronic and nuclear dynamics at conical intersections
本研究结合兆电子伏超快电子衍射与超分辨实空间反演算法，在1,3-环己二烯开环反应中以亚埃精度解析两个锥形交叉附近的电子与核瞬态动力学。
The propagation of high-power femtosecond laser pulses in air under conditions of superposed spatial phase modulation is considered theoretically. The numerical simulations are carried out on the basis of the reduced form of nonlinear Schrodinger equation (NLSE) for time-averaged electric field envelope. Initial spatial modulations are applied to pulse wavefront profiling by a staggered (TEM33) phase plate which is simulated numerically. The dynamics of laser pulse self-focusing, filamentation, and post-filamentation self-channeling after the phase plates with variable phase jumps is studied. …
Sensitive and accurate femtosecond pulse characterization via two-photon absorption in Fabry-Pérot laser diodes
本文利用法布里-珀罗激光二极管的双光子吸收效应，系统验证了其在1.5 μm波长下对36-260 fs飞秒脉冲的精确自相关表征能力，实现了对低至53 μW平均功率脉冲的高精度测量。
Amplified ultrashort laser pulses are useful in many fields of science and engineering. Pushing the frontiers of ultrashort pulse generation will lead to new applications in biomedical imaging, communications and sensing. We propose a new, quantum approach to ultrashort pulse generation using transient quantum coherence which predicts order of magnitude stronger pulses generated with lower input energy than in the steady-state regime, reducing the practical heating limitations. This femtosecond quantum-coherent analog of nanosecond Q-switching is not limited by the pulse duration constraints o…
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
Precise and Fast LIDAR via Electrical Asynchronous Sampling Based on a Single Femtosecond Laser
提出基于单台飞秒光学频率梳的异步电脉冲采样 LiDAR，克服采样混叠与低数据利用率限制，在米级非合作目标上实现微米级精度与兆赫兹更新率，并演示高速计量、百万像素每秒三维成像和非接触生命体征检测。
Diffraction-before-destruction imaging with single ultrashort X-ray pulses has the potential to visualise non-equilibrium processes, such as chemical reactions, at the nanoscale with sub-femtosecond resolution in the native environment without the need of crystallization. Here, a nanospecimen partially diffracts a single X-ray flash before sample damage occurs. The structural information of the sample can be reconstructed from the coherent X-ray interference image. State-of-art spatial resolution of such snapshots from individual heavy element nanoparticles is limited to a few nanometers. Furt…
Controlling electron motion with attosecond precision by shaped femtosecond intense laser pulse
本文提出时间双缝干涉仪方案，通过整形飞秒激光脉冲精确测量电场并控制电子隧穿波包，实现阿秒精度的电子亚周期动力学控制，并经量子轨迹蒙特卡罗和三维含时薛定谔方程验证。
We investigate ultrafast dynamics of the lowest singlet excited electronic state in liquid nitrobenzene using Ultrafast Transient Polarization Spectroscopy (UTPS), extending the well-known technique of Optical-Kerr Effect (OKE) spectroscopy to excited electronic states. The third-order non-linear response of the excited molecular ensemble is highly sensitive to details of excited state character and geometries and is measured using two femtosecond pulses following a third femtosecond pulse that populates the S1 excited state. By measuring this response as a function of time delays between the …
Impulsive orientation of symmetric-top molecules excited by two-color femtosecond pulses is considered. In addition to the well-known transient orientation appearing immediately after the pulse and then reemerging periodically due to quantum revivals, we report the phenomenon of field-free long-lasting orientation. Long-lasting means that the time averaged orientation remains non-zero until destroyed by other physical effects, e.g. intermolecular collisions. The effect is caused by the combined action of the field-polarizability and field-hyperpolarizability interactions. The dependence of deg…
We theoretically investigate the dynamical Franz-Keldysh effect in femtosecond time resolution, that is, the time-dependent modulation of a dielectric function at around the band gap under an irradiation of an intense laser field. We develop a pump-probe formalism in two distinct approaches: first-principles simulation based on real-time time-dependent density functional theory and analytic consideration of a simple two-band model. We find that, while time-average modulation may be reasonably described by the static Franz-Keldysh theory, a remarkable phase shift is found to appear between the …
Ultrafast control of magnetization on the nanometer length scale, in particular all-optical switching, is key to putting ultrafast magnetism on the path towards future technological application in data storage technology. However, magnetization manipulation with light on this length scale is challenging due to the wavelength limitations of optical radiation. Here, we excite transient magnetic gratings in a GdFe alloy with a periodicity of 87 nm by interference of two coherent femtosecond light pulses in the extreme ultraviolet spectral range at the free electron laser facility FERMI. The subse…
A novel polarization-modulation transient method has been developed for studying fast anisotropic relaxation in electronic excited states of polyatomic and biologically relevant molecules under excitation with femtosecond laser pulses. The method is based on the modulation of pump beam polarization with a photo-elastic modulator and detection of an anisotropic contribution to the transient signal by a highly-sensitive demodulation balanced scheme. The method was tested on aqueous solution of coenzyme NADH (nicotin-amideadenine-dinucleotide) pumped at 360 nm and probed at 720 nm. Anisotropic vi…
High-order Mie resonance and transient field enhancement in laser-driven plasma nanoshells
本研究通过高阶米氏共振在等离子体纳米壳体中实现暂态场增强，优化了激光-等离子体相互作用，用于诊断和高能离子生产。
Fundamental interactions induced by lattice vibrations on ultrafast time scales become increasingly important for modern nanoscience and technology. Experimental access to the physical properties of acoustic phonons in the THz frequency range and over the entire Brillouin zone is crucial for understanding electric and thermal transport in solids and their compounds. Here, we report on the generation and nonlinear propagation of giant (1 percent) acoustic strain pulses in hybrid gold/cobalt bilayer structures probed with ultrafast surface plasmon interferometry. This new technique allows for un…
High-order harmonic generation by femtosecond laser pulse in the presence of a moderately strong terahertz (THz) field is studied under the strong field approximation, showing a simple proportionality of near-cutoff even-order harmonic (NCEH) amplitude to the THz electric field. The formation of the THz induced-NCEHs is analytically shown for both continuous wave and Gaussian pulse. The perturbation analysis with regard to the frequency ratio of the THz field to the femtosecond pulse shows the THz-induced NCEHs originates from its first-order correction, and the available parametric conditions…
Visualizing ultrafast dynamics at the atomic scale requires time-resolved pump-probe characterization with femtosecond temporal resolution. For single-shot ultrafast electron diffraction (UED) with fully relativistic electron bunch probes, existing techniques are limited by the achievable electron probe bunch length, charge, and timing jitter. We present the first experimental demonstration of pump-probe UED with THz-driven compression and time-stamping that enable UED probes with unprecedented temporal resolution. This technique utilizes two counter-propagating quasi-single-cycle THz pulses g…
Discovery of transient topological crystalline order in optically driven SnSe
本研究利用飞秒带隙以上激发与时间/角分辨光电子能谱，在平庸绝缘体 SnSe 中发现亚皮秒瞬态拓扑晶态序，并结合 DFT 证明晶格对称性瞬态提升是其成因。
Simultaneous measurements of hard X-ray by a Geiger counter and audible sound (10 Hz-20kHz) by a microphone from a thin water film in air were carried out under intense single and double pulse irradiations of femtosecond laser (35 fs, 800 nm, 1 kHz). Emission profiles of X-ray and sound under the single pulse irradiation by changing the water film position along the laser incident direction (Z-axis) show the same peak positions with a broader emission in sound (403μm at FWHM) than in X-ray (37μm). Under the double pulse irradiation condition with the time delay at 0 ps and 4.6 ns, it was clear…
In our work, we have engineered low capacitance single quantum dot photodiodes as sensor devices for the optoelectronic sampling of ultrafast electric signals. By the Stark effect, a time-dependent electric signal is converted into a time-dependent shift of the transition energy. This shift is measured accurately by resonant ps laser spectroscopy with photocurrent detection. In our experiments, we sample the laser synchronous output pulse of an ultrafast CMOS circuit with high resolution. With our quantum dot sensor device, we were able to sample transients below 20 ps with a voltage resolutio…
Femtosecond Temporal Phase-Resolved Nonlinear Optical Spectroscopy in Molecules with Lock-in Enabled Phase Tracking
本文提出一种结合软件锁相放大与光谱干涉的相位跟踪方案，用于测量分子超快非线性光信号的超弱电场，无需主动稳定即可校正干涉漂移，并展示了其在 impulsively aligned 分子中的应用。
Femtosecond point-projection microscopy (fs-PPM) is an electron microscopy technique that possesses a combination of high spatio-temporal resolution and sensitivity to local electric fields. This allows it to visualize ultrafast charge carrier dynamics in complex nanomaterials. We benchmark the capability of the fs-PPM technique by imaging the ultrafast dynamics of charge carriers produced by multiphoton ionization of silver nanowires. The space-charge driven motion of photoelectrons is followed on \mbox{sub-100}\,nm length scales, while the dynamics are captured on 30-100 fs time scales. The …
Electromagnetic radiation within the terahertz (THz) frequency range is of great interest for applications in remote sensing and time-domain spectroscopy. The laser-induced plasmas are promising mediums for generating THz radiation. It has been recently reported that focusing femtosecond Bessel pulses inside dielectrics induces a high aspect ratio over-critical plasmas. Here we show that the intense resonantly driven electrostatic fields at the so-called critical surface lead to THz radiation emission. Through three-dimensional particle-in-cell simulation and analytical derivation, we have inv…
Understanding the chirality of molecular reaction pathways is essential for a broad range of fundamental and applied sciences. However, the current ability to probe chirality on the time scale of chemical reactions remains very limited. Here, we demonstrate time-resolved photoelectron circular dichroism (TRPECD) with ultrashort circularly polarized vacuum-ultraviolet (VUV) pulses from a table-top source. We demonstrate the capabilities of VUV-TRPECD by resolving the chirality changes in time during the photodissociation of atomic iodine from two chiral molecules. We identify several general ke…
Rippled area formed by surface plasmon polaritons upon femtosecond laser double-pulse irradiation of silicon: the role of carrier generation and relaxation processes
本文通过数值模拟研究飞秒双脉冲照射硅时载流子产生与弛豫对表面波纹形成的影响，定量解释了LSFL面积随脉冲延迟下降的两个时间常数。
We theoretically investigate the generation of ultrafast currents in insulators induced by strong few-cycle laser pulses. Ab initio simulations based on time-dependent density functional theory give insight into the atomic-scale properties of the induced current signifying a femtosecond-scale insulator-metal transition. We observe the transition from nonlinear polarization currents during the laser pulse at low intensities to tunnelinglike excitation into the conduction band at higher laser intensities. At high intensities, the current persists after the conclusion of the laser pulse considere…
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