Jitter-free 40-fs 375-keV electron pulses directly accelerated by an intense laser beam and their application to direct observation of laser pulse propagation in a vacuum

ジッターフリーな超短パルスな電子ビームを実証 --超短パルス電子による超高速な電磁場観察--. 京都大学プレスリリース. 2020-12-04.We report the generation of ultrashort bright electron pulses directly driven by irradiating a solid target with intense femtosecond laser pulses. The duration of electron pulses after compression by a phase rotator composed of permanent magnets was measured as 89 fs via the ponderomotive scattering of electron and laser pulses, which were almost at the compression limit due to the dispersion of the electron optics. The electron pulse compression system consisting of permanent magnets enabled extremely high timing stability between the laser pulse and electron pulse. The long-term RMS arrival time drift was below 14 fs in 4 h, which was limited by the resolution of the current setup. Because there was no time-varying field to generate jitter, the timing jitter was essentially reduced to zero. To demonstrate the capability of the ultrafast electron pulses, we used them to directly visualize laser pulse propagation in a vacuum and perform 2D mapping of the electric fields generated by low-density plasma in real time

Search for sub-eV scalar and pseudoscalar resonances via four-wave mixing with a laser collider

The quasi-parallel photon-photon scattering by combining two-color laser fields is an approach to produce resonant states of low-mass fields in laboratory. In this system resonances can be probed via the four-wave mixing process in the vacuum. A search for scalar and pseudoscalar fields was performed by combining 9.3 $\mu$J/0.9 ps Ti-Sapphire laser and 100 $\mu$J/9 ns Nd:YAG laser. No significant signal of four-wave mixing was observed. We provide the upper limits on the coupling-mass relation for scalar and pseudoscalar fields, respectively, at a 95\% confidence level in the mass region below 0.15~eV.Comment: Accepted by Prog. Theor. Exp. Phy

Relationships between Stratospheric Quasi-Biennial Oscillation (QBO) and Precipitation Activities in Asia

The influence of stratospheric quasi-biennial oscillation (QBO) on global precipitation features was studied over a 25-year period. The years from 1980 to 2004 are classified into easterlyand westerly phases of QBO. Composite analyses in Asia reveal noteworthy pluvial anomalies near the Philippines, and inactive front activity and typical drought events due to adiabatic descent over Japan during the easterly phase of QBO. Cool summers and extreme rainfall events in Japan tend to prevail in the westerly phase. In particular, ten Typhoons struck Japan in 2004 accompanied by the westerly phase of QBO

d-Psicose Inhibits Intestinal α-Glucosidase and Suppresses the Glycemic Response after Ingestion of Carbohydrates in Rats

d-psicose is one of the rare sugars present in small quantities in commercial carbohydrates and agricultural products. In this study, we investigated the effects of d-psicose on the activities of α-amylases and α-glucosidases in vitro, and evaluated the effects of d-psicose on the in vivo postprandial glycemic response using rats. In the in vitro study, d-psicose potently inhibited the intestinal sucrase and maltase, however, slightly inhibited the intestinal and salivary α-amylase activities. Male Wistar rats (6 months old) were administrated 2 g/kg of sucrose, maltose or soluble starch together with 0.2 g/kg of d-psicose or d-fructose. The d-psicose significantly inhibited the increment of plasma glucose concentration induced by sucrose or maltose. The starch-induced glycemic response tended to be suppressed by d-psicose, however the suppression was not significant. These results suggest that d-psicose inhibits intestinal sucrase and maltase activities and suppresses the plasma glucose increase the normally occurs after sucrose and maltose ingestion. Thus, d-psicose may be useful in preventing postprandial hyperglycemia in diabetic patients when foods containing sucrose and maltose are ingested

Modulation of left ventricular diastolic distensibility by collateral flow recruitment during balloon coronary occlusion

AbstractOBJECTIVESThe goals of this study were to elucidate the scaffolding effect of blood-filled coronary vasculature and to determine the functional role of recruited collateral flow in modulating left ventricular (LV) distensibility during balloon coronary occlusion (BCO).BACKGROUNDAlthough LV distensibility is an important factor affecting acute dilation after myocardial infarction, the response of LV diastolic pressure–volume (P-V) relations to coronary occlusion is inconsistent in humans.METHODSMicromanometer and conductance derived LV P-V loops were serially obtained from 16 patients undergoing percutaneous transluminal coronary angioplasty. Coronary collateral flow recruitment was angiographically evaluated by contralateral and ipsilateral contrast injection during BCO.RESULTSIn the group with poor collateral flow (grades 0–I; n = 8), BCO resulted in a downward and rightward shift of the diastolic P-V relations, where end-diastolic volume (EDV) increased by 13% (p < 0.05) without appreciable change in end-diastolic pressure (EDP; 18 ± 6 to 18 ± 8 mm Hg). In contrast, BCO in the group with good collateral flow (grades II–III; n = 8) shifted the diastolic P-V relations upward to the right with a concomitant increase in minimal pressure (min-P; 6 ± 4 to 10 ± 5 mm Hg, p < 0.05), EDP (15 ± 7 to 21 ± 9 mm Hg, p < 0.05) and EDV (+10%, p < 0.05). Reactive hyperemia after balloon deflation caused a rapid and parallel upward shift of the diastolic P-V relations with a marked increase in min-P and EDP, especially in the group with poor collateral flow, before any improvement in LV contraction or relaxation abnormalities.CONCLUSIONSGrades of coronary filling, either retrograde or anterograde, abruptly modulate LV distensibility through the rapid scaffolding effect of coronary vascular turgor

Directional linearly polarized terahertz emission from argon clusters irradiated by noncollinear double-pulse beams

It has been demonstrated that the interaction between argon clusters and intense femtosecond double laser pulses with appropriate intervals in time and space provides important properties for terahertz electromagnetic wave generation, namely, high forward directivity, power enhancement, and linear polarization with a variable direction. Irradiating argon clusters with double pulses (1 and 3 mJ, 40 fs, 810 nm) in 133-ps and 40-μm intervals results in terahertz wave emission in the forward direction that is 10 times greater than that for a single pulse. The polarization direction of terahertz electromagnetic waves can be varied by changing the relative focal positions of the first and second pulses

Demonstration of periodic nanostructure formation with less ablation by double-pulse laser irradiation on titanium

By pairing femtosecond laser pulses (duration ∼40 fs and central wavelength ∼810 nm) at an appropriate time interval, a laser-induced periodic surface structure (LIPSS) is formed with much less ablation than one formed with a single pulse. On a titanium plate, a pair of laser pulses with fluences of 70 and 140 mJ/cm² and a rather large time interval (>10 ps) creates a LIPSS with an interspace of 600 nm, the same as that formed by a single pulse of 210 mJ/cm², while the double pulse ablates only 4 nm, a quarter of the ablation depth of a single pulse