50mJ超短脉冲KrF激光系统的参数优化

介绍了原子能院建立的钛宝石 /KrF混合型激光装置 ,主要输出参数的测量和性能优化。放电泵浦准分子激光器采用离轴放大结构 ,结合棱镜对进行GVD补偿 ,获得 5 0mJ,2 2 0fs的紫外超短脉冲。用4 0cm透镜聚焦 ,靶上功率密度达到 10 17W/cm2 。     

Multipurpose device for nonperturbative photoelectron diagnostics of high-energy H− ion beams

A method of nonperturbative photoelectron diagnostics of a high-energy negative-ion beam proposed earlier by one of the authors is briefly discussed. A multipurpose device using the proposed method of a relativistic H⁻ ion beam in straight-line segments of the transportation channel is described in detail. The beamprobing photonic targets are formed by diaphragming polarized radiation of an Nd:YAG laser. The ion energy (momentum) distributions in transverse and longitudinal phase spaces are promptly determined from the spatial distributions of photoelectrons formed at the corresponding detectors after passing through a homogeneous-field 180° magnetic analyzer.     

50mJ超短脉冲KrF激光系统的参数优化

 介绍了原子能院建立的钛宝石/KrF混合型激光装置，主要输出参数的测量和性能优化。放电泵浦准分子激光器采用离轴放大结构，结合棱镜对进行GVD补偿，获得50mJ，220fs的紫外超短脉冲。用40cm透镜聚焦，靶上功率密度达到10¹⁷ W/cm²。     

Measurement of the Gaponov-Miller force produced in vacuum by tightly focused intense femtosecond laser radiation

A method for measuring the Gaponov-Miller force (GMF) is demonstrated based on the deflection of a picosecond photoelectron beam exposed to tightly focused intense femtosecond laser radiation. It is shown experimentally that the action of this force produced by femtosecond laser pulses linearly depends on their intensity. The method can be used to verify the correctness of measuring the duration of an ultrashort electron bunch based on the GMF.     

Diffusion and aggregation of Ag n -clusters ( n =2-9) on HOPG probed by fs-two-photon-photoemission

The diffusion and aggregation of preformed Ag_n-clusters ( n = 2-9) deposited onto a highly oriented pyrolytic graphite (HOPG) substrate is studied by two-photon-photoemission (2PPE). The sample is irradiated with ultrashort laser pulse pairs and the kinetic energy of the emitted photoelectrons is analyzed in a magnetic bottle type time-of-flight spectrometer. During annealing of the sample from 100 K up to room temperature, nanoparticles are formed on the surface by diffusion and aggregation of the silver clusters. A steep increase of the total photoelectron yield at a sample temperature of about 150 K is explained by the excitation of plasmons in the silver nanoparticles. From the kinetic energy distribution of the photoelectrons we deduce a strong variation of the work function of the sample during the formation of the nanoparticles, which is attributed to a quantum size effect.     

Wide-spectrally-tunable CW and femtosecond linear fiber lasers with ultrabroadband loop mirrors based on fiber circulators

It is demonstrated for the first time that the fiber circulator-based loop reflectors exhibit an extremely wide spectral range. Fiber reflectors based on a commercially available circulator for a wavelength of 1064 nm provide a reflectance of greater than 90% (50%) in a spectral band with a width of 75 (180) nm. The application of such a reflector in a linear CW Yb laser in combination with the second prism reflector allows the smooth tuning of the laser wavelength in the range with a width of greater than 90 nm. The application of two ultrabroadband circulator-based reflectors in the linear all-fiber all-positive-dispersion mode-locked Yb laser makes it possible to generate unique combined femtosecond-picosecond pulses whose shortest component has a duration of less than 190 fs. The spectrum of ultrashort pulses is smoothly tuned in the range 1065–1115 nm owing to the prism reflector.     

Ultrafast dynamics of o-fluorophenol studied with femtosecond time-resolved photoelectron and photoion spectroscopy

The ultrafast dynamics of o-fluorophenol via the excited states has been studied by femtosecond time-resolved photoelectron imaging. The photoion and photoelectron spectra taken with a time delay between 267 nm pump laser and 800 nm probe laser provide a longer-lived S1 electronic state of about ns timescale. In comparison,the spectra obtained by exciting the S2 state with femtosecond laser pulses at 400 nm and ionizing with pulses at 800 nm suggest that the S2 state has an ultrashort lifetime about 102 fs and reflects the internal conversion dynamics of the S2 state to the S1 state.     

Formation of ultrashort electron pulses on scattering of an electron beam by a standing laser wave of ultrashort duration

The scattering of a well collimated electron beam by a strong standing laser wave of ultrashort duration, giving rise to a great number of scattered photons, is considered. This type of scattering is found to cause an electron beam to divide effectively into two parts. Ultrashort laser pulses are shown to be capable of forming ultrashort electron bunches whose length is governed by the laser beam diameter.     

Generation of a directed nanolocalized photoelectron beam by means of femtosecond laser pulses

A directed photoelectron beam is obtained when photoelectrons from a sharp metal tip irradiated by femtosecond laser pulses are passed through a quartz nanocapillary. Such a nanolocalized photoelectron train makes it possible to conduct experiments with simultaneous femtosecond time and nanometer spatial resolutions.     

Photoelectron emission for layers of finite thickness

Basic tools that describe the energy and angular distributions of photoelectrons emitted by inhomogeneous targets are presented. These are the functions of reflection and transmission, the function of photoelectron emission, the equation for photoelectron flow, and the equation for the transmission function, which describes the dynamics of the angular and energy spectra of photoelectrons when they move in the tar-get. The determining influence of the effects of multiple elastic scattering on the angular distribution of photoelectrons is shown. It is demonstrated in which way and by how much the effect of brightness body rotation, well known in optics, influences the X-ray photoelectron spectroscopy signal. Along with analytical solutions, the results of simulation of the X-ray photoelectron spectroscopy signals are presented.     

Group-delay Dispersion in Double-prism Pair and Limitation in Broadband Laser Pulses

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紫外超短脉冲激光放大过程中脉宽压缩的方案设计

采用放电泵浦KrF准分子激光放大器放大波长为248.4nm的紫外超短脉冲激光。对于能量为0.7mJ、脉宽为550fs的输入脉冲,在光束直径保持10mm不变的条件下,能量放大到15mJ,脉宽展宽到1200fs。为了压缩输出脉冲宽度,分析了群速度色散和自相位调制效应对脉宽展宽的影响。利用棱镜对,采用4种不同的实验方案对脉冲引入负的线性频率啁啾,以补偿KrF准分子激光放大器CaF2窗镜中的群速度色散和自相位调制对脉冲引入的正的线性频率啁啾。结果表明:在放大器之前放置棱镜对的方式可以在保持输出脉冲能量为15mJ的同时,在棱镜对间距为110cm的条件下,将输出脉冲宽度压缩到370fs,输出波长为248.4nm、带宽为0.4nm。     

Kerr Lens Mode-locked Operation of Yb:KYW Laser

Using a modified ABCD-matrix approach accounting for nonlinear refraction in active medium,the ranges of cavity parameters that provide a mode-locking of Yb∶KYW-laser in usual z-fold cavity configuration are determined.Taking the cavity parameters that provide a most efficient mode locking and based on fluctuation model,a numerical simulation of laser operation is performed.In the calculations the side-band pump power of 6W at 982 nm is used in 1 cm length KYW crystal with 1 cm×0.005 cm beam cross section.Calculations show that self-starting operation is possible with these parameters and dispersion compensation allows for bandwidth-limited ultrashort pulse generation.The shortest pulse duration was determined to be about 200 fs with self-starting buid-up time of 130 μs.Such a built-up time is comparable and even shorter than that one for the lasers with semiconductor saturable absorbers.The region of negative dispersion provided by prism pair for a stable ultrashort pulse generation was determined to be (-17000～-42000)fs2.     

Observation of fine structures in laser-driven electron beams using coherent transition radiation

We have measured the coherent optical transition radiation emitted by an electron beam from laser-plasma interaction. The measurement of the spectrum of the radiation reveals fine structures of the electron beam in the range 400-1000 nm. These structures are reproduced using an electron distribution from a 3D particle-in-cell simulation and are attributed to microbunching of the electron bunch due to its interaction with the laser field. When the radiator is placed closer to the interaction point, spectral oscillations have also been recorded, signature of the interference of the radiation produced by two electron bunches delayed by 74 fs. The second electron bunch duration is shown to be ultrashort to match the intensity level of the radiation. Whereas transition radiation was used at longer wavelengths in order to estimate the electron bunch length, this study focuses on the ultrashort structures of the electron beam.     

Surface Plasma Waves at a Rough Interface of a Solid

The dispersion law for surface polaritons in an inhomogeneous plasma is obtained and studied. The plasma is formed by surface electron states at the interface of a solid under conditions where the irregularity scale is much greater than the wavelength. It is shown that the irregularity of the plasma results in spatial dispersion of surface electrostatic oscillations.     

强激光与等离子体相互作用产生的超强太赫兹辐射

超短强激光脉冲在等离子体中传播时会激发大振幅的等离子体尾波场，它是一种电子等离子体波．由于这是一种静电波，它一般不能转换成电磁辐射．我们发现在不均匀等离子体中激发的尾波场在一定条件下可以通过线性模式转换产生电磁辐射．由于用超短强激光脉冲尾波场可以达到的电场振幅达100GV／m，其振动频率在太赫兹（10^12Hz）附近，用这种方法可以产生电场强度达到GV／m的太赫兹辐射．     

皮秒激光抽运高压H_2的受激拉曼散射研究

利用Nd :YAG锁模序列脉冲激光 (10 6 4nm)抽运充有高压H2 的拉曼池 ,输出光束经棱镜分光后投射在屏上 ,在可见光及近紫外光区用彩色胶卷摄得 15个受激拉曼散射光斑 ;经 1m光栅摄谱仪摄谱 ,在 36 5— 6 0 5nm波长范围内得到 6 5条受激拉曼谱线 .通过实验结果与理论计算值的比较 ,证明除了H2 的振动拉曼频移量 4 15 4 6cm- 1 外 ,还有多个振动及转动拉曼频移量共同参与作用 ,从而产生了从紫外到红外众多波长的受激拉曼散射光 .     

Group-delay Dispersion in Double-prism Pair and Limitation in Broadband Laser Pulses

A general expression of group-delay dispersion is obtained without any approximation for a pair of double prisms with an arbitrary apex angle. This expression also includes the change of dispersion resulting from change in insertion of the prism material into the beam by translating prism-pairs. The high-order dispersion can be calculated by means of this expression. The limitation for generation of negative group-delay dispersion by use of prism-pairs is presented for ultrashort laser pulses with broadband spectrum.     

Nondipole Effects in Atomic Ionization Induced by an Intense Counter-Rotating Bicircular Laser Field

Nondipole effects occurring in the process of atomic ionization by an intense, mid-infrared, counter-rotating bicircular laser field are investigated using the strong-field approximation with leading-order nondipole corrections. The time integrals appearing in the expression for the differential ionization rate are computed in two ways: numerically, and by applying the saddle-point approximation. The nondipole corrections introduce an asymmetry in the photoelectron momentum distribution along the field propagation direction. The asymmetry is quantified by the partial average value of the propagation-direction momentum component of the photoelectrons and by the normalized difference of the differential ionization rates computed including and excluding the nondipole corrections. Using the saddle-point approximation, it is investigated how the nondipole corrections change the solutions for direct photoelectrons and how this affects the momentum spectra. The impact of nondipole corrections increases with increasing photoelectron energy. Analysis of the complete photoelectron spectra including both direct and rescattered photoelectrons shows that, in the low-energy region, a shift against the propagation direction occurs. The partial average of the propagation–direction momentum component in the rescattering region exhibits a plateau structure and also a local minimum structure that was recently observed in an experiment with a linearly polarized laser field (Lin et al., Phys Rev. Lett. 128, 023201 (2022)).     

Propagation of intense laser pulses through inhomogeneous ionizinggas profiles

By simultaneously and self-consistently solving Maxwell's equations, the Ammosov-Delone-Krainov (ADK) field ionization equation, and the relativistic cold plasma equations, we have investigated the propagation of intense, ultrashort laser pulses through spatially inhomogeneous longitudinal gas gradients. Along with highly accurate calculations of the spatial and temporal beam profiles of the pulse at the end of various gradients, we have also determined simple scaling rules for the location of the vacuum-gas interface in order to minimize the pulse distortion at the focus. We show the benefits of using either preionized or low-Z gases, and we discuss the implications of this work for plasma-channel laser wakefield acceleration