Microlens Array Laser Transverse Shaping Technique for Photoemission Electron Source

TL;DR

This paper explores the use of microlens arrays to improve laser spot uniformity on photocathodes, aiming to enhance electron beam quality in accelerators by reducing asymmetries caused by laser distortion.

Contribution

It presents an experimental study and analysis of microlens arrays for transverse laser shaping at photocathodes, including characterization and comparison with theoretical models.

Findings

Microlens arrays significantly improve laser spot uniformity.

Enhanced beam quality observed due to better laser shaping.

Good agreement between experimental results and theoretical models.

Abstract

A common issue encountered in photoemission electron sources used in electron accelerators is distortion of the laser spot due to non ideal conditions at all stages of the amplification. Such a laser spot at the cathode may produce asymmetric charged beams that will result in degradation of the beam quality due to space charge at early stages of acceleration and fail to optimally utilize the cathode surface. In this note we study the possibility of using microlens arrays to dramatically improve the transverse uniformity of the drive laser pulse on UV photocathodes at both Fermilab Accelerator Science \& Technology (FAST) facility and Argonne Wakefield Accelerator (AWA). In particular, we discuss the experimental characterization of the homogeneity and periodic patterned formation at the photocathode. Finally, we compare the experimental results with the paraxial analysis, ray tracing and wavefront propagation software.