Fig. 1: Multispectral COTR imaging experiments. | Nature Photonics

Fig. 1: Multispectral COTR imaging experiments.

From: Revealing the three-dimensional structure of microbunched plasma-wakefield-accelerated electron beams

Fig. 1

Experimental setup (top) and representative electron spectra (top right) for three injection schemes. The total charge above 100 MeV was 54 pC (down-ramp), 280 pC (STII) and 865 pC (self-injection). The laser pulses are focused to a 20 μm spot in the 3-mm-long helium gas jet, creating a plasma of electron density ne = 2.3 × 1018 cm−3 (down-ramp and STII) or 4 × 1018 cm−3 (self-injection) and a nonlinear wake. For down-ramp injection, a knife edge perturbed the gas flow, creating a shock near the jet entrance; for STII, the gas was doped with 1% nitrogen. Representative single-shot, eight-panel COTR image sets (bottom) from three types of injection (rows), bandpass filtered (10 nm FWHM) at eight wavelengths (columns), acquired on the same shots as the electron spectra in the top right. The yellow dashed lines on 400 nm images exemplify the method for defining the area of each pattern. Each image uses a grey scale that optimizes the visibility of its details.

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