Single-shot measurement of the spectral envelope of broad-bandwidth terahertz pulses from femtosecond electron bunches

Abstract

We present a new approach (demonstrated experimentally and through modeling) to characterize the spectral envelope of a terahertz (THz) pulse in a single shot. The coherent THz pulse is produced by a femtosecond electron bunch and contains information on the bunch duration. The technique, involving a single lowpower laser probe pulse, is an extension of the conventional spectral encoding method (limited in time resolution to hundreds of femtoseconds) into a regime only limited in resolution by the laser pulse length (tens of femtoseconds). While only the bunch duration is retrieved (and not the exact charge profile), such a measurement provides a useful and critical parameter for optimization of the electron accelerator.

Complete characterization of laser wakefield acceleration

“…Bunch duration measurements up to now have relied on techniques utilizing THz radiation emitted by the electrons while passing through a boundary yielding upper limits for the electron pulse length corresponding to a temporal resolution of ≥ 30 fs [7][8] [9] [10]. Recently, parallel to our work, few-femtosecond features of the electron pulses have been observed indirectly from the transition radiation spectrum [11].…”

Diagnostics of electron beams and plasma wave in laser-plasma accelerators

“…To account for the shot-to-shot variations of the electron beam properties various single shot version have been developed [21,22]. The spectral encoding geometry [22,23] modulates the spectrum of a chirped probe pulse with some limitations on the temporal resolution. It delivers the THz electric field in a single spectral measurement, which can be fitted by assuming a generating electron bunch temporal structure.…”

“…It delivers the THz electric field in a single spectral measurement, which can be fitted by assuming a generating electron bunch temporal structure. Some enhancements to this technique [23] might further improve the temporal resolution to reach the probe pulse duration. The noncollinear cross-correlation or temporal decoding geometry [24,25] offers a simple way to single shot and high temporal resolution characterization.…”

High-Acquisition-Rate Single-Shot Pump-Probe Measurements Using Time-Stretching Method

“…Recent efforts have therefore been focused to allow the capture of an entire ultrafast signal waveform in a single probe shot, which is of particular advantage in terahertz (THz) and other varieties of ultrafast spectroscopy123. Single-shot techniques make possible measurements of photoinduced irreversible phenomena, asynchronous or chaotic phenomena, and phenomena with potential picosecond shot-to-shot jitter, such as the timing of pulses from a laser system synchronized to an x-ray free electron laser pulse45678. Because of the increasing interest in and importance of understanding these and other phenomena, single-shot diagnostic tools are becoming more crucial in the field of ultrafast spectroscopy.…”

“…This is a variation on spectrally-encoded single-shot measurements, where the probe pulse is linearly chirped, and the temporal signal is thus encoded in the probe spectrum5914. Instead of observing the spectrum with a grating and a 2-D detector, the probe pulse and encoded temporal dynamics are further chirped to nanosecond time scales using the group velocity dispersion in the optical fiber, thus slowing down the ultrafast signal to time scales easily recorded with fast detectors and high-bandwidth electronics.…”