Capturing the non-equilibrium state in light–matter–free-electron interactions through ultrafast transmission electron microscopy

Ultrafast transmission electron microscope(UTEM) with the multimodality of time-resolved diffraction, imaging,and spectroscopy provides a unique platform to reveal the fundamental features associated with the interaction between free electrons and matter. In this review, we summarize the principles, instrumentation, and recent developments of the UTEM and its applications in capturing dynamic processes and non-equilibrium transient states. The combination of the transmission electron microscope with a femtosecond laser via the pump–probe method guarantees the high spatiotemporal resolution, allowing the investigation of the transient process in real, reciprocal and energy spaces. Ultrafast structural dynamics can be studied by diffraction and imaging methods, revealing the coherent acoustic phonon generation and photoinduced phase transition process. In the energy dimension, time-resolved electron energy-loss spectroscopy enables the examination of the intrinsic electronic dynamics of materials, while the photon-induced near-field electron microscopy extends the application of the UTEM to the imaging of optical near fields with high real-space resolution. It is noted that light–free-electron interactions have the ability to shape electron wave packets in both longitudinal and transverse directions, showing the potential application in the generation of attosecond electron pulses and vortex electron beams.

Leser-Trélat征并发前列腺癌1例

患者男，58岁。因躯干部皮肤起黑褐色斑丘疹20年余．近2个月突然增多来我科就诊。患者诉20年前下腹部长褐色斑丘疹，无明显自觉症状，遂未予治疗。近5年来皮损渐累及胸、背部及双上肢共约二四百个，近2个月突然增加一百多个．原有皮疹亦较前面积增大。发病以来，无发热乏力，精神尚可，饮食正常，大小便正常。

恶性黑棘皮病并发Leser-Trélat征1例

患者男,72岁。全身褶皱部、乳晕肥厚、色素沉着3个月,周身泛发性丘疹伴剧痒2个月。皮肤科情况:颈部、腋窝、腹股沟、肛周皮肤肥厚、色素沉着,呈绒毛状或乳头瘤样增生,双侧乳头和乳晕角化、色素沉着,颈部、躯干及四肢散在米粒至黄豆大肤色至淡褐色角化性丘疹及斑丘疹。皮损组织病理示(上胸部):表皮角化过度,棘层肥厚,乳头瘤样增生,基底层色素增加;(右侧腹股沟):表皮中度角化过度,乳头瘤样增生,乳头似指样向上凸出,棘层中度肥厚,基底层色素增加,真皮浅层少许淋巴细胞浸润。诊断:恶性黑棘皮病并发Leser-Trélat征。

Leser-Trélat征

报告1例Leser-Trélat(莱泽-特雷拉)征并发鼻咽癌。患者男,70岁。30年前躯干部出现脂溢性角化,近3个月胸部皮损突然增多并出现呼吸困难,CT及鼻咽部病灶组织病理检查证实为鼻咽癌。

初诊为脂溢性角化病的Leser-Trelat征一例

Leser-Trelat征是指成年人突然出现大量瘙痒性脂溢性角化皮损合并内脏恶性肿瘤的征象。如果脂溢性角化病患者皮损短期内出现体积增大、数量增多并伴瘙痒,常提示内脏肿瘤,应进行相关排癌检查,特别是皮损的表皮生长因子免疫组化分析。本文就1例脂溢性角化病的Leser-Trelat征合并肺癌患者的诊治过程进行报道,以提高临床医师对该病的认识。

恶性黑棘皮病并发Leser-Trélat征

报告1例恶性黑棘皮病并发Leser-Trélat征。患者男,69岁。全身褶皱部位皮肤色素沉着、乳头瘤样增生,伴瘙痒半年。皮肤科检查:颜面部、双侧腹股沟、腋窝、肛周皮肤色素沉着,呈绒毛状或乳头瘤样增生;双眼睑缘和唇红区及颊黏膜乳头瘤样增生。双侧乳头和乳晕角化及色素沉着,颈部、上胸部、腹部及四肢可见米粒至黄豆大疣状角化性丘疹。胃镜检查及胃黏膜组织病理检查示贲门-胃底低分化腺癌。诊断:恶性黑棘皮病并发Leser-Trélat征。

恶性黑棘皮病并发Leser-Trélat征及牛肚掌

报告1例恶性黑棘皮病并发Leser-Trélat征及牛肚掌。患者男,77岁。面部、腋窝变黑7个月,躯干及上肢褐黑色斑丘疹6个月,1年前行胃癌根治性切除术。皮肤科检查:面部、颈部、胸部、背部及双上肢可见200余个米粒至黄豆大圆形或椭圆形扁平褐色斑丘疹。面部及双侧腋窝可见色素沉着,腋下、眶周及唇部乳头瘤样病变,双侧手掌散在粟粒状细小光滑乳头状凸起,呈牛肚掌样外观。皮损组织病理检查:角化过度,棘层肥厚呈乳头瘤样增生,棘层内可见角囊肿。诊断:恶性黑棘皮病并发Leser-Trélat征及牛肚掌。

Review of fully coherent free-electron lasers

Generation of intense, fully coherent radiation with wide spectral coverage has been a long-standing challenge for laser technologies. Several techniques have been developed in recent years to extend the spectral coverage in optical physics, but none of them hold the potential to produce X-ray laser pulses with very high-peak power. Urgent demands for intense X-ray light sources have prompted the development of free-electron lasers(FELs), which have been proved to be very useful tools in many scientific areas. In this paper, we give an overview of the basic principle of FELs, techniques for realizing fully coherent FELs, and the development of fully coherent FEL facilities in China.

Picosecond terahertz pump-probe realized from Chinese terahertz free-electron laser

Electron energy relaxation timeτis one of the key physical parameters for electronic materials.In this study,we develop a new technique to measureτin a semiconductor via monochrome picosecond(ps)terahertz(THz)pump and probe experiment.The special THz pulse structure of Chinese THz free-electron laser(CTFEL)is utilized to realize such a technique,which can be applied to the investigation into THz dynamics of electronic and optoelectronic materials and devices.We measure the THz dynamical electronic properties of high-mobility n-GaSb wafer at 1.2 THz,1.6 THz,and 2.4 THz at room temperature and in free space.The obtained electron energy relaxation time for n-GaSb is in line with that measured via,e.g.,four-wave mixing techniques.The major advantages of monochrome ps THz pump-probe in the study of electronic and optoelectronic materials are discussed in comparison with other ultrafast optoelectronic techniques.This work is relevant to the application of pulsed THz free-electron lasers and also to the development of advanced ultrafast measurement technique for the investigation of dynamical properties of electronic and optoelectronic materials.

Effect of normalized plasma frequency on electron phase-space orbits in a free-electron laser

Irregular phase-space orbits of the electrons are harmful to the electron-beam transport quality and hence deteriorate the performance of a free-electron laser （FEL）. In previous literature, it was demonstrated that the irregularity of the electron phase-space orbits could be caused in several ways, such as varying the wiggler amplitude and inducing sidebands. Based on a Hamiltonian model with a set of self-consistent differential equations, it is shown in this paper that the electron- beam normalized plasma frequency functions not only couple the electron motion with the FEL wave, which results in the evolution of the FEL wave field and a possible power saturation at a large beam current, but also cause the irregularity of the electron phase-space orbits when the normalized plasma frequency has a sufficiently large value, even if the initial energy of the electron is equal to the synchronous energy or the FEL wave does not reach power saturation.

Vacuum Ultraviolet Free-Electron Laser Photoionization Mass Spectrometry of Alpha-pinene Ozonolysis

α-pinene is the most abundant monoterpene that represents an important family of volatile organic compounds.Molecular identification of key transient compounds during theα-pinene ozonolysis has been proven to be a challenging experimental target because of a large number of intermediates and products involved.Here we exploit the recently developed hybrid instruments that integrate aerosol mass spectrometry with a vacuum ultraviolet free-electron laser to study theα-pinene ozonolysis.The experiments ofα-pinene ozonolysis are performed in an indoor smog chamber,with reactor having a volume of 2 m^(3) which is made of fluorinated ethylene propylene film.Distinct mass spectral peaks provide direct experimental signatures of previously unseen compounds produced from the reaction ofα-pinene with O_(3).With the aid of quantum chemical calculations,plausible mechanisms for the formation of these new compounds are proposed.These findings provide crucial information on fundamental understanding of the initial steps ofα-pinene oxidation and the subsequent processes of new particle formation.

Three-dimensional simulation of long-wavelength free-electron lasers with helical wiggler and ion-channel guiding

A three-dimensional simulation of a steady-state amplifier model of a long-wavelength free-electron laser （FEL） with realizable helical wiggler and ion-channel guiding is presented. The set of coupled nonlinear differential equations for electron orbits and fields of TE 11 mode in a cylindrical waveguide are solved numerically by the Runge–Kutta algorithm with averages calculated by the Gaussian quadrature technique. Self-fields and space-charge effects are neglected, and the electron beam is assumed to be cold and slippage is ignored. The parameters correspond to the Compton regime. Evolution of the radiation power and growth rate along the wiggler is studied. Ion-channel density is chosen to obtain optimum efficiency. Simulations are preformed for the FEL operating in the neighborhood of 35 GHz and 16.5 GHz for the electron beam energies of 250 keV and 400 keV, respectively. The result of the saturated efficiency was found to be in good agreement with the simple estimation based on the phase-trapping model.

Efficiency enhancement of a two-beam free-electron laser using a nonlinearly tapered wiggler

A nonlinear and non-averaged model of a two-beam free-electron laser （FEL） wiggler that is tapered nonlinearly in the absence of slippage is presented. The two beams are assumed to have different energies, and the fundamental resonance of the higher energy beam is at the third harmonic of the lower energy beam. By using Maxwell＇s equations and the full Lorentz force equation of motion for the electron beams, coupled differential equations are derived and solved numerically by the fourth-order Runge-Kutta method. The amplitude of the wiggler field is assumed to decrease nonlinearly when the saturation of the third harmonic occurs. By simulation, the optimum starting point of the tapering and the slopes for reducing the wiggler amplitude are found. This technique can be applied to substantially improve the efficiency of the two-beam FEL in the XUV and X-ray regions. The effect of tapering on the dynamical stability of the fast electron beam is also studied.

ANGULAR SPECTRUM PROPERTY OF SPONTANEOUS EMISSION IN A TWO-DIMENSIONAL UNDULATOR FREE-ELECTRON LASER

The angular spectrum of spontaneous emission in a two-dimensional undulator free-electron laser is analyzed theoretically. Numerical calculation shows that the 3-th harmonic spontaneous emission power density can be greatly enhanced by using a two-dimensional undulator, for which l=s, so the harmonic number can be selected by selecting l. Therefore, the higher harmonic operation of a free-electron laser can be realized selectively.

Dispersion relation and growth rate for a corrugated channel free-electron laser with a helical wiggler pump

The effects of corrugated ion channels on electron trajectories and spatial growth rate for a free-electron laser with a one-dimensional helical wiggler have been investigated. Analysis of the steady-state electron trajectories is performed by solving the equations of motion. Our results show that the presence of a corrugated channel shifts the resonance frequency to smaller values of ion channel frequency. The sixth-order dispersion equation describing the coupling between the electrostatic beam mode and the electromagnetic mode has also been derived. The dispersion relation characteristic is analyzed in detail by numerical solution. Results show that the growth rate of instability in the presence of corrugated ion channels can be greatly enhanced relative to the case of an uniform ion channel.

Theoretical study of the enhancement of saturable absorption of Kr under x-ray free-electron laser

The generation of hollow atoms will reduce the probability of light absorption and provide a high-quality diffraction image in the experiment. In this paper, we calculated the ionization rate of the Kr atom under x-ray free-electron laser(XFEL) using Hartree–Fock–Slater model and simulated the ionization model of Kr atom using Monte–Carlo method to determine the response of the hollow atom of Kr atom to the XFEL photon energy. Calculating the correlation between the total photoionization cross-section of the ground state of Kr atom and the photon energy, we determined three particular photon energies of 1.75 ke V, 1.90 ke V, and 14.30 ke V. The dynamics simulation under the experimental condition's17.50 ke V photon energy was achieved by implementing the Monte–Carlo method and calibrating the photon flux modeling parameters. Consequently, our calculated data are more consistent with experimental phenomena than previous theoretical studies. The saturable absorption of Kr at 1.75 ke V, 1.90 ke V, 14.30 ke V, and 17.50 ke V energies was further investigated by using the optimized photon flux model theory. We compared the statistics on main ionization paths under those four specific photon energies and calculated the population changes of various Kr hollow atoms with different configurations.The results demonstrate that the population of hollow atoms produced at the critical ionization photon energy is high. Furthermore, the change of population with respect to position is smooth, which shows a significant difference between the generation mode of ions with low and high photon energies. The result is important for the study of medium-and high-Z element hollow atoms, which has substantial implications for the study of hollow atoms with medium and high charge states, as well as for the scaling of photon energy of free electron lasers.

Effects of self-fields on electron trajectory and gain in planar wiggler free-electron lasers with two-stream and ion-channel guiding

The effects of self-fields on electron trajectories and gain in planar wiggler free-electron lasers with two-stream and ion-channel guiding are investigated. An analysis of the two-stream quasi-steady-state electron trajectories is given by solving the equation of motion in the presence of ion-channel guiding and the planar wiggler. The electron trajectories and the gain are derived. The stability of the trajectories, the characteristics of the linear gain, and the normalized maximum gain are studied numerically. The numerical calculations show that there are eight group trajectories rather than the two groups reported in the absence of the self-fields. It is also shown that the normalized gain group seven （G7） decreases while the rest increases with the increase in normalized ion-channel frequency. The two-stream instability and the self-field lead to a decrease in the maximum gain, except for G7.

Synchrotron-Infrared Microscopy Analysis of Amyloid Fibrils Irradiated by Mid-Infrared Free-Electron Laser

Amyloid fibrils are widely recognized as a cause of serious amyloidosis such as Alzheimer’s disease. Although dissociation of amyloid fibril aggregates is expected to lead to a decrease in the toxicity of the fibrils in cells, the fibril structure is robust under physiological conditions. We have irradiated amyloid fibrils with a free-electron laser (FEL) tuned to mid-infrared frequencies to induce dissociation of the aggregates into monomer forms. We have previously succeeded in dissociating fibril structures of a short peptide of the thyroid hormone by tuning the oscillation frequency to the amide I band, but the detailed structural changes of the peptide have not yet been determined at a high spatial resolution. Synchrotron-radiation infrared microscopy (SR-IRM) is a powerful tool for in situ analysis of minute structural changes of various materials, and in this study, the feasibility of SR-IRM for analyzing the microscopic conformational changes of amyloid fibrils after FEL irradiation was investigated. Reflection spectra of the amyloid fibril surface showed that the amide I peaks shifted to higher wave numbers after the FEL irradiation, indicating that the initial β-sheet-rich structure transformed into a mixture of non-ordered and turn-like peptide conformations. This result demonstrates that conformational changes of the fibril structure after the FEL irradiation can be observed at a high spatial resolution using SR-IRM analysis and the FEL irradiation system can be useful for dissociation of amyloid aggregates.

Use of a Mid-Infrared Free-Electron Laser (MIR-FEL) for Dissociation of the Amyloid Fibril Aggregates of a Peptide

Amyloid fibrils are deposited in various tissues in the body, and are linked to the putative causes of serious diseases such as amyloidosis. Although the conditions of the disease would be expected to improve if the fibril structure could be destroyed, the aggregated structure is stable under physiological conditions. Recently, we found that the amyloid fibrils of lysozyme could be refolded into their active form by using a mid-infrared free-electron laser (MIR-FEL) tuned to the amide I band (corresponding to the C=O stretch vibration), with the MIR-FEL having specific oscillation characteristics of a picosecond pulse structure, a tunable wavelength within mid-infrared frequencies, and high photon density. In the study, we tested the usability of the FEL for dissociation of aggregates of pathological amyloid fibrils by using a short peptide of human thyroid hormone. The fibrils (after being placed on a glass slide) were irradiated using the FEL tuned to the amide I band (1644 cm?1), and those in situ were analyzed by Congo-Red assay, scanning-electron microscopy, and transmission-electron microscopy. All of the results obtained using these microscopic analyses indicated that the amyloid fibril formation was considerably decreased by FEL irradiation. Moreover, upon irradiation, a strong fibril peak at the amide I band in the infrared spectrum was transformed into a broad peak. These results imply that the β-sheet-rich structure of the amyloid fibrils changed into non-ordered or unspecified structures after the FEL irradiation. This FEL irradiation system, combined with various analytical methods, shows promise for the dissociation of amyloid aggregates.

Electron-Cyclotron Laser Using Free-Electron Two-Quantum Stark Radiation in a Strong Uniform Axial Magnetic Field and an Alternating Axial Electric Field in a Voltage-Supplied Pill-Box Cavity

We consider the radiation from the beam electrons traveling in a strong uniform axial magnetic field and an axial alternating electric field of wavelength Aw generated by a voltage-supplied pill-box cavity. The beam electrons emit genuine laser radiation that propagates only in the axial direction through free-electron two- quantum Stark radiation. We find that laser radiation takes place only at the expense of the axial kinetic energy when Aw 〈〈 c/（ωc/γ）, where ωc/γ is the relativistic electron--cyclotron frequency. We formulate the laser power based on quantum-wiggler electrodynamics, and envision a laser of length lore with estimated power 0.1 GW/（kA） in the 10-4 cm wavelength range.