Single-shot spectra of temporally selected micropulses from a mid-infrared free-electron laser by upconversion

We demonstrate the measurement of single-shot spectra of temporally selected micropulses from a mid-infrared (MIR) free-electron laser (FEL) by upconversion. We achieve the upconversion of FEL pulses at 11 \mu m using externally synchronized Nd:YAG or microchip laser pulses at 1064 nm to produce sum-frequency mixing (SFM) signals at 970 nm, which are detected by a compact CCD spectrometer without an intensifier. Our experimental system is very cost-effective, and allows us to obtain the laser spectra of selected micropulses at any temporal position within a single macropulse from an oscillator-type FEL.Comment: 3 pages, 4 figure

Record high extraction efficiency of free electron laser oscillator

共振器型自由電子レーザの世界最高変換効率を達成 --長波長赤外での強光子場の実現とアト秒X線源の開発に大きく前進--. 京都大学プレスリリース. 2020-10-13.The highest extraction efficiency (9.4%) of a free electron laser (FEL) oscillator has been achieved at the midinfrared FEL facility of Kyoto University. Because of the interaction between the electron beam and FEL electromagnetic field, a maximum electron energy decrease of 16% was observed. The measured energy decrease was consistent with the measured FEL spectrum. An FEL micropulse energy of ~100 μJ with the expected few-cycle pulse duration at a wavelength of 11 μm was observed. This result is an important milestone for the high-extraction-efficiency FEL oscillator and will contribute to the strong-field physics of atoms and molecules

Full characterization of few-cycle superradiant pulses generated from a free-electron laser oscillator

The detailed structure of few-cycle superradiant pulses generated from a free-electron laser (FEL) oscillator was experimentally revealed for the first time. As predicted in numerical simulations, the obtained pulse structures have ringing, i.e., a train of subpulses following the main pulse. Owing to the phase retrieval with a combination of linear and nonlinear autocorrelation measurements, the temporal phase was also obtained with the pulse shape, and $\pi$-phase jumps between each pulse were confirmed. This particular pulse shape with $\pi$-phase jumps is a common feature of Burnham-Chiao ringing or superradiance ringing. Using unaveraged FEL simulations, the ringing was found to originate from repeated formation and deformation of microbunches across successive bunch slices. The simulation results imply that there should be superluminal propagation of the FEL pulse due to strong gain modulation along the undulator of the FEL oscillator.Comment: Main: 16 pages, 5 figures, Supplementary material: 10 pages, 10 figures, 1 vide

The Particle-Tracking Simulation of a New Photocathode RF Gun in the Free-Electron Laser Facility, KU-FEL

A project is underway that aims to generate attosecond pulses via high-harmonic generation in rare gases, driven by extremely short and highly intense pulses from free-electron-laser oscillators. For this purpose, it has been planned that a new photocathode RF gun, dedicated to high-bunch-charge operation, will be installed at the KU-FEL (Kyoto University Free Electron Laser) oscillator facility. In this study, RF guns with two different structures (1.6-cell and 1.4-cell) were compared, from the perspective of exploring the possibility of introducing bunch-interval modulation, which is important for achieving high extraction efficiency in the FEL oscillator. As a result, it was confirmed that the introduction of bunch-phase modulation would be possible only in the case of the 1.6-cell RF gun. After the structure of the RF gun was decided on, particle-tracking simulations were performed, to study the electron-beam parameters using the 1.6-cell RF gun and 1 nC bunch charge. The results showed that we could obtain the peak current of 1 kA without a large degradation of the other parameters

Development of Phonon Dynamics Measurement System by MIR- FEL and Pico-second Laser

FEL2015, Daejeon, Republic of KoreaCoherent control of a lattice vibration in bulk solid (mode-selective phonon excitation: MSPE) is one of the attractive methods in the solid state physics because it becomes a powerful tool for the study of ultrafast lattice dynamics (e.g. electron-phonon interaction and phonon-phonon interaction). Not only for that, MSPE can control electronic, magnetic, and structural phases of materials. In 2013, we have directly demonstrated MSPE of a bulk material with MIR-FEL (KU-FEL) by anti-Stokes Raman scattering spectroscopy. For the next step, we are starting a phonon dynamics measurement to investigate the difference of physical property between thermally excited phonon (phonon of equilibrium state) and optically excited phonon (phonon of non-equilibrium state) by time-resolved method in combination with a pico-second VIS laser. By using pico-second laser, we also expect to perform the anti-Stokes hyper-Raman scattering spectroscopy to extend MSPE method to the phonon mode which has Raman inactive . As the first step, we have commissioned the time-resolved phonon measurement system and started measurement on 6H-SiC. In this conference, we will present the outline of measurement system, and experimental results

ネツ インキョク コウシュウハ デンシジュウ ニ ヨル チュウセキガイ ジユウ デンシ レーザヨウ コウヒンシツ デンシ ビーム セイセイ

京都大学0048新制・課程博士博士(エネルギー科学)甲第14846号エネ博第200号新制||エネ||45(附属図書館)27252UT51-2009-F488京都大学大学院エネルギー科学研究科エネルギー変換科学専攻(主査)准教授 増田 開, 教授 長﨑 百伸, 教授 大垣 英明学位規則第4条第1項該当Doctor of Energy ScienceKyoto UniversityDA

Study for electron-hole plasma on semiconductor surface at mid-infrared region

Although semiconductor is a good transparent material for the radiation with the wavelength from mid to far infrared, it becomes highly reflective when the electron-hole plasma is formed on the surface by irradiating the femto- or picosecond laser pulse. Thus, it is possible to use as a reflective switch with high-speed response for the radiation of mid to far infrared range. In this project, we will reveal the reflective characteristics and dynamics of the plasma switch for the mid infrared range at the KU-FEL. At present we are designing the optics and layout for the experiment and making the comparison with the experimental results at the far infrared range. We will show the design of optics for the experiment at KU-FEL and the discussion for the characteristics of the plasma switch at the mid infrared range deduced from the results at the far infrared range.The 11th International Symposium of Advanced Energy Scienc

Upgrade Projects of Mid-Infrared Free Electron Laser at Kyoto University for High Peak Power and Ultra-short Pulse Operation

A mid-infrared Free Electron Laser (MIR-FEL) is a candidate to realize a high-repetition-rate attosecond hard X-ray source based on the high harmonic generation (HHG). A new project to conduct proof of principle experiment of HHG driven by a MIR-FEL has been started from November 2018. For this purpose, upgrade projects of MIR-FEL at Kyoto University (KU-FEL) has been started to achieve high peak power and ultra-short pulse operation