We report subpicosecond electro-optic measurements of the length of individual relativistic electron bunches. The longitudinal electron-bunch shape is encoded electro-optically on to the spectrum of a chirped laser pulse. The electron-bunch length is determined by analyzing individual laser-pulse spectra obtained with and without the presence of an electron bunch. Since the length of the chirped laser pulse can be easily changed, the electron bunch can be visualized on different time scales. This single-shot imaging technique is a promising method for real-time electron-bunch diagnostics.
1 Significant differences in the overwintering densities of predatory carabid and staphylinid beetles and spiders occurred on an 'island' grassy bank habitat composed of blocks of Agrostis stolonifera, Dactylis glomerata, Holcus lanatus and Lolium perenne, within and between winters during a 7-year study. 2 Densities of the predators over the last three winters of the study were greater in the bank than in the boundary of the field in which the bank was situated. 3 Succession occurred in plots of L. perenne, with D. glomerata fully replacing this species. Plots of D. glomerata and H. lanatus remained virtually monospecific. 4 Over the period of study, the beetle bank maintained its role in providing overwintering habitat for polyphagous predators and carabid diversity has increased since the bank was first established. Beetle banks were therefore shown to contribute to conservation biodiversity in an agroecosystem.
Electro-optic detection of the Coulomb field of a relativistic electron bunch combined with single-shot cross correlation of optical pulses is used to enable single-shot measurements of the shape and length of femtosecond electron bunches. This method overcomes a fundamental time-resolution limit of previous single-shot electro-optic measurements, which arises from the inseparability of time and frequency properties of the probing optical pulse. Using this new technique we have made real-time measurements of a 50 MeV electron bunch, observing the profile of 650 fs FWHM ( approximately 275 fs rms) long bunches.
Given the limitations of a retrospective audit and reliability of the data, this result nevertheless compares favourably with reported figures in the literature.
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