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Photo-Modification of Melanin by a Mid-Infrared Free-Electron Laser
摘要： Melanin is rigidly constructed by several nitrogen-containing aromatic rings, and its excess accumulation in skin tissue is closely associated with melanosis. Although visible lasers (wavelength: 600–1000 nm) are conventionally used for the photo-thermolysis of melanocyte, several pigmented nevi are difficult to be treated. Here, we propose an alternate method for targeting the molecular structure of melanin using an infrared free electron laser (FEL) tuned to 5.8 μm that corresponds to the stretching vibrational mode of carboxylate group. A drastic morphological change on the black-colored surface of melanin powder were observed after the pulse irradiation with a power of 500 mJ/cm2, and the minimum irradiation time for damage to the morphology was 1.4 seconds. Analyses by mass spectroscopy, infrared spectroscopy, and 13C-nuclear magnetic resonance implied that a pyrrole group was removed by the FEL irradiation. In addition, the FEL irradiation dispersed almost all of the melanoma cells from a culture solution without any influence on other ingredients in the medium, and one-cell analysis by infrared microscopy showed that the structure of melanoma could be substantially damaged by the irradiation. This study proposes the potency of intense mid-infrared laser as novel alternative way to reduce melanin.
关键词： Infrared free electron laser,Melanoma,Vibrational mode,Melanin,Photo-modification
更新于2025-11-21 11:03:13
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Two- and Three-Photon Partial Photoionization Cross Sections of Li+, Ne8+ and Ar16+ under XUV Radiation
摘要： In this work, we present the photon energy dependence of the two- and three-photon cross sections of the two-electron Li+, Ne8+ and Ar16+ ions, following photoionization from their ground state. The expressions for the cross sections are based on the lowest-order (non-vanishing) perturbation theory for the electric field, while the calculations are made with the use of an ab initio configuration interaction method. The ionization cross section is dominated by pronounced single photon resonances in addition to peaks associated with doubly excited resonances. In the case of two-photon ionization, and in the non-resonant part of the cross section, we find that the 1D ionization channel overwhelms the 1S one. We also observe that, as one moves from the lowest atomic number ion, namely Li+, to the highest atomic number ion, namely Ar16+, the cross sections generally decrease.
关键词： free-electron laser,X-ray radiation,cross sections,lowest-order perturbation theory,multiphoton ionization
更新于2025-09-23 15:23:52
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Measurement of bunch length evolution in electron beam macropulse of S-band linac using coherent edge radiation
摘要： Intense coherent edge radiation (CER) with a power of 0.10 mW was observed in a straight line with an undulator of Kyoto University Free Electron Laser (KU-FEL). To investigate the evolution of a bunch length in a macropulse of an electron beam, a technique was developed using the CER beam. The measured air-extracted CER beam pro?le has a hollow structure resembling the ?rst-order Laguerre–Gaussian mode with asymmetric intensity in horizontal direction. It roughly agrees with the pro?le calculated considering the effective area of a de?ection mirror employed to extract the beam from the FEL optical cavity into air. The root-mean-squared (RMS) bunch length determined from a measured spectrum of the CER beam is 60 μm for an electron-beam macropulse. Changes in the CER intensity in the electron-beam macropulse were measured by diode detectors with short time constants at two frequencies. The evolution of the RMS bunch length was determined using the ratio of the CER intensity at the two frequencies. It could be concluded that the evolution correlated with the macropulse structure of the FEL power. Therefore, measuring the evolution of the CER intensity at multiple frequencies proved useful to control FEL macropulses.
关键词： Bunch length,Terahertz,Coherent edge radiation,Free-electron laser,Linac
更新于2025-09-23 15:23:52
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Software Platform for European XFEL: Towards Online Experimental Data Analysis
摘要： Large amount of data being generated at large scale facilities like European X-ray Free-Electron Laser (XFEL) requires new approaches for data processing and analysis. One of the most computationally challenging experiments at an XFEL is single-particle structure determination. In this paper we propose a new design for an integrated software platform which combines well-established techniques for XFEL data analysis with High Performance Data Analysis (HPDA) methods. In our software platform we use streaming data analysis algorithms with high performance computing solutions. This approach should allow analysis of the experimental dataflow in quasi-online regime.
关键词： single particle imaging,X-ray Free-Electron Laser,High Performance Data Analysis,X-ray Cross-Correlation Analysis,Expectation-Maximization
更新于2025-09-23 15:22:29
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Angular and Spectral Bandwidth of Extreme UV Multilayers Near Spacer Material Absorption Edges
摘要： High resolution imaging systems for EUV range are based on multilayer optics. Current generation of EUV lithography uses broadband Sn LPP sources, which requires broadband mirrors to fully utilize the source power. On the other hand, there always remains a possibility to use FEL or synchrotron as EUV source. FEL can produce very bright narrowband EUV light of a tunable wavelength, and the spectral bandwidth of the mirror is no longer a restriction. In this paper we look at the consequences of switching to different wavelengths if FEL source is used. For instance, it is known that the reflectance of Mo/Si multilayers increases when approaching Si L-edge, and the spectral bandwidth drops. But the behavior of an angular bandwidth (and its relation with the spectral bandwidth) is usually left out. It is also sometimes assumed that these bandwidths are correlated. For a large aperture EUV optical system with diffraction-limited resolution angular acceptance of a mirror is also a very important parameter. We show that the angular bandwidth of several multilayer systems (Mo/Si, Mo/Be, Ru/Si, Ru/B, La/B) actually increases close to spacer absorption edges, opposite to what occurs with the spectral bandwidth. We study this effect and show that it is caused by an interplay of changing optical constants of respective materials used in these multilayer combinations. We also provide an experimental check of the angular bandwidth of Mo/Si multilayers at 13.5 and 12.6 nm, which confirms our calculations.
关键词： Multilayer,Free Electron Laser,EUV Photolithography
更新于2025-09-23 15:22:29
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Possibilities for serial femtosecond crystallography sample delivery at future light sourcesa)
摘要： Serial femtosecond crystallography (SFX) uses X-ray pulses from free-electron laser (FEL) sources that can outrun radiation damage and thereby overcome long-standing limits in the structure determination of macromolecular crystals. Intense X-ray FEL pulses of sufficiently short duration allow the collection of damage-free data at room temperature and give the opportunity to study irreversible time-resolved events. SFX may open the way to determine the structure of biological molecules that fail to crystallize readily into large well-diffracting crystals. Taking advantage of FELs with high pulse repetition rates could lead to short measurement times of just minutes. Automated delivery of sample suspensions for SFX experiments could potentially give rise to a much higher rate of obtaining complete measurements than at today’s third generation synchrotron radiation facilities, as no crystal alignment or complex robotic motions are required. This capability will also open up extensive time-resolved structural studies. New challenges arise from the resulting high rate of data collection, and in providing reliable sample delivery. Various developments for fully automated high-throughput SFX experiments are being considered for evaluation, including new implementations for a reliable yet flexible sample environment setup. Here, we review the different methods developed so far that best achieve sample delivery for X-ray FEL experiments and present some considerations towards the goal of high-throughput structure determination with X-ray FELs.
关键词： automation,serial femtosecond crystallography,X-ray free-electron laser,sample delivery,high-throughput
更新于2025-09-23 15:22:29
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Beam phase retrieval based on higher order modes in cylindrical superconducting radio frequency cavities
摘要： The control of beam phase relative to the accelerating RF field within a superconducting cavity is important in many accelerator applications and is of particular importance for a free electron laser facility. As standard practice, the phase is usually inferred from the beam-induced transient field with respect to a timing reference. We report here on an alternative and novel means of beam phase determination based on beam-excited higher order electromagnetic modes and the accelerating electromagnetic mode, which are conveniently available from the same coupler. The monopole modes are immune to the electron beam offset and therefore are best suited for the task. A coupled circuit model is used to assist the development and to rapidly assess the facility of the method. Simulations based on the circuit model indicate that the resolution of this system depends critically on the signal to noise ratio. Beam-based measurements with a test setup were carried out at the European X-ray Free Electron Laser (XFEL), Germany. Based on this new method, we have routinely obtained a resolution of 0.1°. The best resolution observed with the current setup was 0.03°. These results agree very well with the predictions from those predicted by a circuit model. The system investigated here can be used to provide diagnostic information for the current low level RF system employed in the European XFEL. To this end, the associated electronics are under development. This monitor is the first of its kind that can deliver direct and online measurements of the beam phase with respect to the RF field.
关键词： higher order modes,accelerator applications,beam phase retrieval,free electron laser,superconducting radio frequency cavities
更新于2025-09-23 15:21:21
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An Ellipsometric Technique with an ATR Module and a Monochromatic Source of Radiation for Measurement of Optical Constants of Liquids in the Terahertz Range
摘要： Measuring the optical constants of liquids, especially water-containing solutions, is very difficult in the terahertz range. The well-known methods of measurement of the refractive index and absorption coefficient in this range include time-domain spectroscopy and Fourier-transform spectrometry. We have developed a highly sensitive ellipsometry method for measuring the optical constants of liquids using the tunable monochromatic radiation from the Novosibirsk free-electron laser. The ellipsometer is supplemented with an internal reflection module for the measurement of highly absorbing samples. The angle of incidence on the sample in the silicon prism of the module has been optimized for maximum sensitivity to parameters to measure. Measurements of the optical constants of various liquids have been performed, and a sensitivity of 0.01 has been demonstrated.
关键词： Internal reflection ellipsometry,Free electron laser,Aqueous solution,Terahertz range
更新于2025-09-23 15:21:21
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[IEEE 2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz2018) - Nagoya, Japan (2018.9.9-2018.9.14)] 2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Lasing and saturation of CAEP THz FEL facility
摘要： A high power THz free electron laser (FEL) facility is under construction at China Academy of Engineering Physics (CAEP) since October, 2011. The radiation frequency of the FEL facility is designed in range of 1~3 THz and the average output power is about 10 W. First lasing of the CAEP THz FEL (CTFEL) facility was obtained in August 29, 2017. Then the saturation operation is observed in September 20, 2017. The radiation frequency is sequentially as 1.99THz, 2.41THz and 2.92THz. And the average output power is larger than 10 W; the largest output power is about 20W. The peak power of micro-pulse is larger than 0.5MW. The optical resonator of CTFEL is optimized to ensure wavelength tunable in a wide range and high power operation. In this paper, the main designed and present status of the facility is given.
关键词： free electron laser,lasing,CAEP,saturation,FEL,THz
更新于2025-09-23 15:21:01
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Effect of a tightly focused chirped Gaussian laser pulse on electron acceleration in helical undulator
摘要： The chirped-pulse inverse free electron laser (CIFEL) interaction has been investigated by considering a tightly focused chirped Gaussian laser pulse and a helical undulator in vacuum. We consider the more realistic description of a laser, i.e., seventh-order calculation in the spatial term and first-order calculation in the temporal term. Numerical calculations show that better electron acceleration can be achieved using a tightly focused chirped Gaussian laser pulse in the CIFEL scheme. The investigation shows that a 10 MeV electron can be accelerated up to a few giga-electron volts energy with the present available laser parameters.
关键词： CIFEL,tightly focused chirped Gaussian laser pulse,helical undulator,electron acceleration,chirped-pulse inverse free electron laser
更新于2025-09-23 15:19:57