Abstract
We study the efficiency limitation affecting laser-induced coherent synchrotron radiation (CSR) at high laser power. Experiments are made on the UVSOR-II storage ring in conditions of narrowband terahertz CSR emission. While, at moderate power, CSR power increases quadratically with laser power, a noticeable decrease in efficiency and eventually a decrease in CSR power is observed experimentally at high power. Details of the underlying process are analyzed numerically. As the saturation effect depends almost instantaneously on the laser intensity, the saturation occurs locally in longitudinal space. This has important consequences on the modulation pattern induced on the electron bunch.
Highlights
We study the efficiency limitation affecting laser-induced coherent synchrotron radiation (CSR) at high laser power
Experiments are made on the UVSOR-II storage ring in conditions of narrowband terahertz CSR emission
A relativistic electron bunch can radiate coherent synchrotron radiation (CSR) in the terahertz domain when its longitudinal charge density distribution presents Fourier components at terahertz frequencies. This happens in short electron bunches [1,2], and in long electron bunches in which a longitudinal modulation has been performed. Such modulated bunch experiments have been realized in the conditions of slicing [3,4,5,6,7,8], in which an external laser creates a picosecond/subpicosecond ‘‘dip’’ in the longitudinal charge distribution, leading to broadband short terahertz emission
Summary
Pulses (duration 300 ps FWHM, energy 70 mJ) at 10 Hz. We constructed a custom external grating compressor delivering pulses, the duration of which is adjustable in a wide range (from 191 ps to full compression), providing another way to adjust the peak power. We constructed a custom external grating compressor delivering pulses, the duration of which is adjustable in a wide range (from 191 ps to full compression), providing another way to adjust the peak power For this purpose, we placed one of the gratings on a long range translation stage (60 cm) and carefully designed the compressor so that the introduced delay was almost independent of the distance between gratings. Near the maximum laser pulse duration available from the pulse shaper (191 ps FWHM), only a slight (though noticeable) departure from quadratic scaling is observed [Fig. 4(b)].
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