Abstract
The need for precisely defined beam shapes in photoelectron sources has been well established. In this paper, we use a spatial light modulator and simple shaping algorithm to create arbitrary, detailed transverse laser shapes with high fidelity. We transmit this shaped laser to the photocathode of a high voltage dc gun. Using beam currents where space charge is negligible, and using an imaging solenoid and fluorescent viewscreen, we show that the resultant beam shape preserves these detailed features with similar fidelity. Next, instead of transmitting a shaped laser profile, we use an active feedback on the unshaped electron beam image to create equally accurate and detailed shapes. We demonstrate that this electron beam feedback has the added advantage of correcting for electron optical aberrations, yielding shapes without skew. The method may serve to provide precisely defined electron beams for low current target experiments, space-charge dominated beam commissioning, as well as for online adaptive correction of photocathode quantum efficiency degradation.
Highlights
For any photoemitted electron beam, the 3D intensity distribution of the laser determines the initial density distribution of the electrons
In this paper we demonstrate that using a commercially available liquid crystal spatial light modulator (Hamamatsu LCOS-SLM X10468-04) in the transverse plane to shape a drive laser, a low current beam from high voltage dc gun imaged onto a target plane can be shaped with high accuracy
We show that a simple method of SLM-based laser shaping, the polarization subtractive method, enables us to generate arbitrary to generate arbitrary low-current electron beam shapes of high accuracy from photoelectron sources
Summary
For any photoemitted electron beam, the 3D intensity distribution of the laser determines the initial density distribution of the electrons. In this paper we demonstrate that using a commercially available liquid crystal spatial light modulator (Hamamatsu LCOS-SLM X10468-04) in the transverse plane to shape a drive laser, a low current beam from high voltage dc gun imaged onto a target plane can be shaped with high accuracy. This method has been shown in [18] to have nearly equivalent performance in terms of accuracy and efficiency to the best Fourier space method We demonstrate that this method has both the ability to offer a precise transverse shape for beam dynamics purposes, and the adaptive capability to correct for imperfections in the quantum efficiency of a photocathode. We will show that using an active feedback with an unshaped beam, we can achieve high fidelity beam shapes free from electron optical aberrations and QE nonuniformities present in our system
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