Ilya A. Shkrob, Dmitri A. Oulianov, Robert A. Crowell, Stanislas Pommeret
Single-shot ultrafast absorbance spectroscopy based on the frequency encoding of the kinetics is analyzed theoretically and implemented experimentally. In Part II of the series, arbitrary thickness sample is analysed theroretically. The model is then used to simulate the results for a-Si:H films.
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Single-shot ultrafast absorbance spectroscopy based on the frequency encoding of the kinetics is analyzed theoretically and implemented experimentally. The kinetics are sampled in the frequency domain using linearly chirped, amplified 33 fs FWHM pulses derived from a Ti:sapphire laser. A variable length grating pair compressor is used to achieve the time resolution of 500-1000 channels per a 2-to-160 ps window with sensitivity > 5x10-4. In terms of the acquisition time, FDSS has an advantage over the pump-probe spectroscopy in a situation when the "noise" is dominated by amplitude variations o…
"Single-shot" ultrafast spectroscopy based on the frequency encoding of transient absorbance kinetics using chirped probe pulses is analyzed theoretically. FDSS has an advantage over pump-probe spectroscopy in a situation where the "noise" is dominated by amplitude variations of the signal. Unlike "single-shot" techniques based on spatial encoding of the kinetics, no a priori knowledge of the excitation profile of the pump is needed. FDSS spectroscopy can be used for many types of samples, liquid or solid, including those comparable in thickness to the wavelength of the probe light. Another ad…
Single-shot ultrafast spectroscopy based on the frequency encoding of transient absorbance kinetics (FDSS) is demonstrated. These kinetics are sampled spectrally using linearly chirped pulses derived from a Ti:sapphire laser. A variable length grating pair compressor is used to provide group velocity dispersion out to -1.6 ps^2 and achieve the sampling of 512 channels per a 2-to-160 ps window with sensitivity > 5e-4. The possibilities of FDSS are illustrated with studies of three photon ionization of liquid water and one-photon excitation of a thin-film
All-optical discrete illumination-based compressed ultrafast photography
针对压缩超快摄影中条纹相机伪影和图像质量折衷问题，提出全光学离散照明压缩超快摄影（AOD-CUP），利用FACED技术实现可调帧数和皮秒至纳秒间隔的高保真快照成像，并成功可视化应力波和等离子体通道。
Terahertz (THz)-based electron manipulation has recently been shown to hold tremendous promise as a technology for manipulating and driving the next-generation of compact ultrafast electron sources. Here, we demonstrate an ultrafast electron diffractometer with THz-driven pulse compression. The electron bunches from a conventional DC gun are compressed by a factor of 10 and reach a duration of ~180 fs (FWHM) with 10,000 electrons/pulse at a 1 kHz repetition rate. The resulting ultrafast electron source is used in a proof-of-principle experiment to probe the photoinduced dynamics of single-crys…
An ultrafast single-pixel optical 2D imaging system using a single multimode fiber (MF) is proposed. The MF acted as the all-optical random pattern generator. Light with different wavelengths pass through a single MF will generator all-optical random speckle patterns, which have a low correlation of 0.074 with 0.1nm wavelength step from 1518.0nm to 1567.9nm. The all-optical random speckle patterns are perfect for compressive sensing (CS) imaging with the advantage of low cost in comparison with the conventional expensive pseudorandom binary sequence (PRBS). Besides, with the employment of phot…
A flexible and accurate total variation and cascaded denoisers-based image reconstruction algorithm for hyperspectrally compressed ultrafast photography
针对高光谱压缩超快摄影重建质量差的问题，提出基于全变分与级联去噪器的TV-CD算法，在即插即用ADMM框架中融合深度去噪先验，提升重建精度与质量，促进实际应用。
We demonstrate a non-invasive time-sorting method for ultrafast electron diffraction (UED) experiments with radio-frequency (rf) compressed electron beams. We show that electron beam energy and arrival time at the sample after rf compression are strongly correlated such that the arrival time jitter may be corrected through measurement of the beam energy. The method requires minimal change to the infrastructure of most of the UED machines and is applicable to both keV and MeV UED. In our experiment with ~3 MeV beam, the timing jitter after rf compression is corrected with 35 fs root-mean-square…
Clean few-cycle blue soliton self-compressed pulses generation in hollow-core fibers
本文通过结合宽带倍频、多板连续谱后压缩与空芯光纤蓝色孤子自压缩，实验实现了4.4 fs清洁蓝色少周期脉冲，并展示了该方案在色散控制、效率和简化结构方面的三重优势。
Low-cost passive single-shot ultrafast imaging at 685 Gfps
本文提出一种低成本被动单次曝光超快成像系统，利用商用微透镜阵列和标准显微镜盖玻片将时间信息映射到多个空间通道，通过消费级CMOS图像传感器实现单次曝光捕捉，达到685 Gfps的帧率。
We interpret the purely spectral forward Maxwell equation with up to 3${^{\rm rd}}$ order induced polarizations for pulse propagation and interactions in quadratic nonlinear crystals. The interpreted equation, also named nonlinear wave equation in frequency domain, includes both quadratic and cubic nonlinearities, delayed Raman effects and anisotropic nonlinearities. The full potential of this wave equation is demonstrated by investigating simulations of solitons generated in the process of ultrafast cascaded second-harmonic generation. We show that a balance in the soliton delay can be achiev…
We report a simple and compact design of a dispersion compensated mode-locked Yb:fiber oscillator based on a nonlinear amplifying loop mirror (NALM). The fully polarization maintaining (PM) fiber integrated laser features a chirped fiber Bragg grating (CFBG) for dispersion compensation and a fiber integrated compact non-reciprocal phase bias device, which is alignment-free. The main design parameters were determined by numerically simulating the pulse evolution in the oscillator and by analyzing their impact on the laser performance. Experimentally, we achieved an 88 fs compressed pulse durati…
10-W Sub-100-fs Ultrafast Cr:ZnS/ZnSe MOPA System enabled by doping gradient engineering
本文报道了一种基于精细调谐掺杂分布的 Cr:ZnS/ZnSe 多晶体的高功率中红外飞秒 MOPA 系统，通过双级放大和色散补偿实现了 10.4 W 平均功率和 78 fs 脉冲持续时间，为中红外超快激光的功率提升和无活动部件应用奠定了基础。
Synthesis of single-cycle pulses based on a Yb:KGW laser amplifier
针对Yb:KGW激光脉冲难以压缩至单周期范围的问题，本研究采用双空心光纤模块展宽光谱，结合光场合成器首次实现该技术体系下的单周期脉冲，为超快光谱等应用提供新可能。
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…
Robust isolated attosecond pulse generation with self-compressed sub-cycle drivers from hollow capillary fibers
本文提出利用压强递减空芯毛细管光纤中的极端孤子自压缩，从多周期红外脉冲产生亚周期驱动光瞬态以驱动高次谐波，实现载波包络相位鲁棒、高对比度的孤立阿秒脉冲直接产生，为集成全光纤IAP源开辟新途径。
Ultrafast electron pulses, combined with laser-pump and electron-probe technologies, allow for various forms of ultrafast microscopy and spectroscopy to elucidate otherwise challenging to observe physical and chemical transitions. However, the pursuit of simultaneous ultimate spatial and temporal resolution has been largely subdued by the low monochromaticity of the electron pulses and their poor phase synchronization to the optical excitation pulses. State-of-the-art photon-driven sources have good monochromaticity but poor phase synchronization. In contrast, field-driven photoemission has mu…
Over the past years, ultrafast lasers with average powers in the 100 W range have become a mature technology, with a multitude of applications in science and technology. Nonlinear temporal compression of these lasers to few- or even single-cycle duration is often essential, yet still hard to achieve, in particular at high repetition rates. Here we report a two-stage system for compressing pulses from a 1030 nm ytterbium fiber laser to single-cycle durations with 5 $μ$J output pulse energy at 9.6 MHz repetition rate. In the first stage, the laser pulses are compressed from 340 to 25 fs by spect…
Gas-filled hollow-core fiber (HCF) pulse post-compressors generating few- to single-cycle pulses are a key enabling tool for attosecond science and ultrafast spectroscopy. Achieving optimum performance in this regime can be extremely challenging due to the ultra-broad bandwidth of the pulses and the need of an adequate temporal diagnostic. These difficulties have hindered the full exploitation of HCF post-compressors, namely the generation of stable and high-quality near-Fourier-transform-limited pulses. Here we show that, independently of conditions such as the type of gas or the laser system…
Addressing modulational instability in anti-resonant hollow-core fibers for pulse compression
本研究通过实验和数值模拟比较两种反谐振空芯光纤，发现合理选择反谐振元件壁厚可显著降低调制不稳定性增益，从而提升超快脉冲压缩的稳定能量上限。
Efficient spectral broadening and few-cycle pulse generation with multiple thin water films
本文提出以多重超薄流动水膜作为非线性介质，实现倍频程超连续谱展宽，并将35 fs脉冲压缩至3.9 fs，进而产生至33阶的高次谐波。
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…
High-Efficiency Plasma-Based Compressor for Ultrafast Soft X-ray Free-Electron Lasers
针对软X射线自由电子激光中传统光学压缩器的效率限制，提出利用高度电离惰性气体等离子体的高效压缩器，在5.2 nm处透射率超70%，可将25 fs脉冲压缩至1.4 fs，峰值功率超100 GW，克服了软X射线CPA效率瓶颈。
Compact, folded multi-pass cells for energy scaling of post-compression
本文提出一种紧凑折叠型多通池（CMPC），通过折叠光束路径缩小装置尺寸，实现高脉冲能量后压缩，实验将8 mJ脉冲从1 ps压缩至51 fs，并具备扩展至200 mJ的潜力。
Shot-noise-limited few-cycle mid-infrared frequency comb with attosecond phase stability
该研究开发了一款基于Cr:ZnS激光器的少周期中红外光频梳，实现了阿秒级相位稳定性与shot噪声受限的振幅稳定性，为量子极限计量等领域提供了新工具。
We present nonlinear pulse compression of a high-power SESAM-modelocked thin-disk laser (TDL) using an Ar-filled hypocycloid-core Kagome Hollow-Core Photonic Crystal Fiber (HC-PCF). The output of the modelocked Yb:YAG TDL with 127 W average power, a pulse repetition rate of 7 MHz, and a pulse duration of 740 fs was spectrally broadened 16-fold while propagating in a Kagome HC-PCF containing 13 bar of static Argon gas. Subsequent compression tests performed using 8.4% of the full available power resulted in a pulse duration as short as 88 fs using the spectrally broadened output from the fiber.…
Near single-cycle pulse generation using a cascaded all-bulk multi-pass cell compression system
该研究用级联全块状多通池压缩系统，从特定初始脉冲产生近单周期脉冲，实验与模拟验证其高效性，为强场等超快应用提供平台。
Passive harmonic mode-locked laser on lithium niobate integrated photonics
本研究在薄膜铌酸锂平台上实现了首个电泵浦自启动被动谐波锁模激光器，产生4.3 ps脉冲，重复率约20 GHz，为紧凑高重复率锁模激光器开辟新路径。
Generation of high power spatially-structured laser pulses via forward Raman amplification in plasma
本研究提出基于等离子体前向拉曼放大（FRA）的通用方案，通过理论建模与粒子模拟证明可将近红外结构种子激光放大1e4~1e5倍并自压缩至拍瓦级亚周期脉冲，为高场物理提供紧凑、高功率结构光产生途径。
Spatially homogeneous few-cycle compression of Yb lasers via all-solid-state free-space soliton management
本文提出利用全固态自由空间孤子管理实现Yb激光脉冲压缩，通过孤子模式传播和限制每层非线性相位小于1.0弧度，将170飞秒脉冲压缩至约9.2飞秒，实现超过50%的效率和约0.87的时空光谱均匀性，为少周期脉冲产生提供了高效、高质量的全固态方案。
We have specifically investigated the free-space mode locking dynamics of erbium-doped fiber (EDF) mode-locked ultrafast lasers via nonlinear polarization rotation (NPR) in the normal dispersion regime. To do so, we built a passively mode-locked fiber laser based on NPR with a repetition rate of 89 MHz producing an octave-spanning spectrum due to supercontinuum (SC) generation in highly nonlinear fiber (HNLF). Most significantly, we have achieved highly stable self-starting NPR mode-locked femtosecond fiber laser based frequency comb which has been running mode locked for the past one year wit…
High-pulse-energy integrated mode-locked lasers based on a Mamyshev oscillator
本文提出一种基于Mamyshev振荡器的高脉冲能量集成模式锁激光器，实现低损耗铒掺杂硅氮光子集成电路中的高能量脉冲输出，突破传统光子集成源的限制。
Streaking of photoelectrons with optical lasers has been widely used for temporal characterization of attosecond extreme ultraviolet pulses. Recently, this technique has been adapted to characterize femtosecond x-ray pulses in free-electron lasers with the streaking imprinted by farinfrared and Terahertz (THz) pulses. Here, we report successful implementation of THz streaking for time-stamping of an ultrashort relativistic electron beam of which the energy is several orders of magnitude higher than photoelectrons. Such ability is especially important for MeV ultrafast electron diffraction (UED…
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