No abstract

A picosecond pulse radiolysis facility based on a laser-driven photocathode electron accelerator has been constructed. First observation of picosecond dynamics in ionic liquid of DEMMA-TFSI in radiation chemistry was reported. It is found that the electrons produced by ionization are solvated to full solvation in ionic liquid with a rate constant of 3.9 × 10 10 s -1 , and dry electrons before full solvation react rapidly with biphenyl and pyrene with rate constant of 3.8 to 7.9 × 10 11 dm 3 mol -1 s -1 . The geminate ion recombination in n-dodecane and n-hexane was also observed by monitoring transient optical absorption at 523 nm.

The molar absorption coefficient and the radiolytic yield of solvated electron in ionic liquid of DEMMA-TFSI were estimated respectively to be 2.3 × 10 4 L mol -1 cm -1 and 0.8 × 10 -7 mol J -1 by observing the reaction and kinetics of solvated electron and dry electron in the ionic liquid. The solvated electron in DEMMA-TFSI has a very broad absorption spectrum peaking at 1100 nm and reacts slowly with pyrene with a rate constant of 3.5 × 10 8 L mol -1 s -1 , while the dry electron is captured rapidly by pyrene with C 37 value of 0.065 mol L -1 .

Multimode terahertz(THz)-wave generation using coherent Cherenkov radiation (CCR) was investigated. The frequency spectra of CCR, which utilized a metal-wrapped hollow dielectric tube of 7 mm outer radius and a picosecond electron bunch of 27 MeV beam energy, were measured by a Michelson interferometer with a 4.2 K silicon bolometer. In this study, discrete spectral components at frequencies of 0.09, 0.14, and 0.36 THz were observed experimentally and explained as transverse magnetic (TM) modes of TM03, TM04, and TM09, respectively, according to a theoretical calculation for the tube.

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.