[Show abstract][Hide abstract] ABSTRACT: By monitoring coherent transition radiation (CTR) with a Michelson interferometer, bunch length measurement was investigated. Less-than-20-fs electron bunches were generated by a photocathode-based linear accelerator (linac) and a magnetic bunch compressor. From the femtosecond electron bunch of 2.1 pC and 32 MeV, CTR was measured using a Michelson interferometer that had two detectors with different spectral ranges, which enhanced the detection spectral range of CTR (ranging from 3 to 50 THz) and enabled us to determine the bunch length of the electron bunch. A model based on the interferometer's frequency sensitivity was proposed and introduced to analyze the measured interferograms. The measured interferograms and the frequency spectra were explained using the model.
Physical Review Special Topics - Accelerators and Beams 07/2014; 17(7). DOI:10.1103/PhysRevSTAB.17.072803 · 1.66 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The solvated electron in room temperature ionic liquids (RTILs) has been the subject of several investigations and several reports exist on its nature and absorption spectrum. These studies concluded that the solvated electron exhibits an absorption spectrum peaking in the 1000–1400 nm region; a second absorption band peaking in the UV region has been assigned to the hole or dication radicals simultaneously formed in the system. Here we report on the fate of the excess electron in the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, P14+/NTf2− using nanosecond pulse radiolysis. Scavenging experiments allowed us to record and disentangle the complex spectrum measured in P14+/NTf2−. We identified a bi-component absorption spectrum, due to the solvated electron, the absorption maxima located at 1080 nm and around 300 nm, as predicted by previous ab-initio molecular dynamics simulations for the dry excess electron. We also measured the spectra using different ionic liquids and confirmed the same feature of two absorption peaks. The present results have important implications for the characterization of solvated electrons in ionic liquids and better understanding of their structure and reactivity.
[Show abstract][Hide abstract] ABSTRACT: Ultrashort electron bunches are essential for time-resolved measurement methods such as pulse radiolysis from the viewpoint of time resolutions. On the other hand, generation of electro-magnetic wave in the THz range using short electron bunches has been investigated. Frequency spectra of coherent transition radiation (CTR) emitted by an electron bunch depend on bunch form factor (BFF), which is expressed by Fourier coefficients of longitudinal distribution in the electron bunch. In this study, the bunch length measurement was demonstrated by analyzing THz-waves generated by CTR. Femtosecond electron bunches were generated by a laser photocathode RF gun linac and magnetic bunch compressor. THz-waves generated by CTR, which was emitted on an interface of an aluminum mirror along the beam trajectory, were transported to a Michelson interferometer. The bunch length was measured by analyzing interferogram, which was an infrared detector output as a function of a moving mirror position. Finally, the bunch length was measured according to fitting curves for the interferogram near the centerburst. Minimum bunch length of 1.3 fs was obtained at a bunch charge of ~1 pC.
[Show abstract][Hide abstract] ABSTRACT: Ultrashort, e.g., picosecond or femtosecond, electron beams are useful for electro-magnetic radiation production in terahertz (THz) range due to the inverse of 1 ps bunch length corresponding to the frequency of 1 THz. The electron beams were generated by a photocathode radio-frequency (RF) gun linac. Electron beams with energy of ̃4 MeV at the RF gun exit were accelerated up to ̃30 MeV in a linac. The accelerated electron beams were compressed by a magnetic bunch compressor, resulting in femtosecond pulse width. THz radiation of the order on 0.1 THz based on coherent Cherenkov radiation (CCR) using hollow dielectric tubes and Smith-Purcell radiation (SPR) using a metallic grating or metasurface were reported.
IEEJ Transactions on Electronics Information and Systems 01/2014; 134(4):502-509. DOI:10.1541/ieejeiss.134.502
[Show abstract][Hide abstract] ABSTRACT: Femto-second pulse radiolysis system is developed for the study of the electron beam induced reaction in materials. Femtosecond electron pulse was generated by optimizing the laser photocathode RF electron gun accelerator. 240 fs time resolution was achieved by femtosecond electron pulse and formation of hydrated electron was observed by femtosecond pulse radiolysis. For more fine time resolution of the pulse radiolysis, the Equivalent velocity spectroscopy (EVS) method is required to avoid degradation of time resolution caused by velocity difference between electron and light in sample.
IEEJ Transactions on Electronics Information and Systems 01/2014; 134(5):664-669. DOI:10.1541/ieejeiss.134.664
[Show abstract][Hide abstract] ABSTRACT: This paper proposes the use of a solid-state plasma lens in the fs linacs, in which the bunch radii of the beams are much larger than the lengths. Although gas plasmas degrade vacuum, solid-state plasmas do not. Another problem is that a return current flowing in the beam region of plasmas decreases the focusing power of the lens. By orientating anisotropic plasmas, we can constrain the return current, while maintaining the focusing power.
Proceedings of the 10th Meeting of Particle Accelerator Society of Japan, Nagoya; 08/2013
[Show abstract][Hide abstract] ABSTRACT: The generation of radially polarized terahertz (THz) waves from a photoconductive antenna (PCA) with radial microstructures was investigated. Microstructured electrodes with 10 μm lines and spaces were fabricated on a semi-insulating InP wafer using photolithography. The PCA with three layers was driven by an amplified femtosecond laser and DC power supply. Radially polarized THz waves from the PCA were measured by a Michelson interferometer with a 4.2 K silicon bolometer. The polarization components of THz waves were analyzed by a wire grid polarizer.
[Show abstract][Hide abstract] ABSTRACT: The kinetics of geminate ion recombination was studied by the
femtosecond pulse radiolysis of n-dodecane with biphenyl solution. The
complicated biphenyl concentration-dependence behaviors of the transient
absorptions at 800 nm are observed and elucidated with a Monte Carlo
simulation of geminate recombination and charge transfer processes in
the biphenyl-dodecane solution. The experimental data suggested the
existence of n-dodecane excited radical cation in the radiolysis. It
plays very important roles especially in the high-concentration
solution. The reaction rate constant of the excited radical cation with
biphenyl molecule was 3.5×1011 dm3
mol-1 s-1, which is comparable with
the reaction rate constant of the electron with biphenyl molecule. The
contributions of the geminate ion recombination, the charge transfer
reaction and the relaxation of the excited radical cation were obtained
as a function of the biphenyl concentration.
[Show abstract][Hide abstract] ABSTRACT: Double-decker pulse radiolysis (DDPR), which utilizes double-decker electron beams, was investigated to develop a new pulse radiolysis with a high time resolution. The double-decker electron beams were generated by injecting two UV pulses into a photocathode radio-frequency gun. In the pulse radiolysis, one electron beam was used as a pump beam, and the other was converted to a probe pulse. Finally, as its first application, the DDPR was successfully used for observing solvated electrons in water, with a 10%-90% rise time of 8.6 ps.
The Review of scientific instruments 07/2012; 83(7):073302. DOI:10.1063/1.4731652 · 1.61 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Pulse radiolysis spectroscopically studies the initial stage of atomic and molecular reactions induced by electron beams. Single-bunched beams with bunch lengths on the order of femtosecond or shorter are fervently requested for this purpose. The laser wake field acceleration is readily applicable now, which is able to realize beams with bunch length of 1 fs, energy of 30 MeV, repetition rate of 1 Hz, bunch charge of 10 pC, energy width of 10%, etc.
International Journal of Modern Physics B 01/2012; 21(03n04). DOI:10.1142/S0217979207042239 · 0.94 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this paper, Smith-Purcell effect, which utilizes metallic grating and electron bunches, was investigated for a new device of terahertz (THz)-wave generation. Femtosecond electron bunches induced multimode THz-wave at a frequency of
Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 2012 37th International Conference on; 01/2012
[Show abstract][Hide abstract] ABSTRACT: In this paper, Smith-Purcell effect, which utilizes metallic grating and electron bunch, was investigated for a new device of terahertz (THz)-wave generation. Electron bunches and metallic gratings realized monochromatic or THz-wave generation at a frequency of <0.7 THz.
[Show abstract][Hide abstract] ABSTRACT: Two ultrashort electron-bunch photocathode RF guns in
picosecond (ps) and femtosecond (fs) time region are reviewed. The ps
gun was developed and used successfully to generate an
ultralow-emittance and high-charge electron beam with normalized
emittance of 1.2 mm-mrad at bunch charge of 1 nC. The low-emittance
electron beam has been used successfully to produce a 100-fs high-charge
electron single bunch with a booster linear accelerator and a magnetic
bunch compressor. An ultrafast pulse radiolysis with time resolution of
240 fs was constructed using the fs electron beam for the study of
ultrafast reactions in radiation chemistry and biology. The fs gun,
developed under the KEK/Osaka University collaboration with a new
structure cavity and many improvements, was succeeded in producing
directly a near-relativistic 100-fs electron beam with energy of 1-3
MeV. Femtosecond time-resolved electron diffraction has been constructed
using the fs RF gun for the study of photon-induced phase transition in
materials. Some experimental results of pulse radiolysis and MeV
electron diffraction in fs time region were reported and discussed.
Journal of the Vacuum Society of Japan 01/2012; 55(2):42-49. DOI:10.3131/jvsj2.55.42
[Show abstract][Hide abstract] ABSTRACT: Femtosecond pulse radiolysis is developed for studies of electron beam induced ultra-fast reaction in matter. 98 fs electron pulse was generated by a photocathode RF (radio frequency) gun linear accelerator (LINAC) with a magnetic bunch compressor. However for more fine time resolution, the Equivalent velocity spectroscopy (EVS) method is required to avoid degradation of time resolution caused by velocity difference between electron and analysing light in sample. In the EVS method, incident analysing light is oblique toward electron beam with an angle associated with refractive index of sample, and then, electron pulse is rotated toward the direction of travel to overlap with light pulse. In previous studies, pulse rotation had not been compatible with pulse compression. However, by oblique incident of light to the photocathode, pulse rotation was compatible with pulse compression, and the time resolution was improved by principle of the equivalent velocity spectroscopy.