Realtime Tomography of Gas-Jets with a Wollaston Interferometer

TL;DR

This paper introduces a real-time, tomographic gas-density diagnostic using a Wollaston interferometer and advanced algorithms to reconstruct three-dimensional, non-symmetric gas jet densities for applications in free electron lasers and laser wakefield acceleration.

Contribution

It presents a novel real-time tomographic algorithm with GPU acceleration for characterizing complex, non-symmetric gas jet density distributions.

Findings

Successful real-time 3D density reconstruction of gas jets.

Application to both low-density and high-density gas jets.

Capability to characterize non-symmetric density profiles with high resolution.

Abstract

A tomographic gas-density diagnostic using a single-beam Wollaston interferometer able to characterise non-symmetric density distributions in gas jets is presented. A real-time tomographic algorithm is able to reconstruct three dimensional density distributions. A Maximum Likelihood -- Expectation Maximisation algorithm, an iterative method with good convergence properties compared to simple back projection, is used. With the use of graphical processing units, real time computation and high resolution are achieved. Two different gas jets are characterised: a kHz, piezo-driven jet for lower densities and a solenoid valve based jet producing higher densities. While the first is planned for to be used in bunch length monitors at the free electron laser at Paul Scherrer Institut (PSI, SwissFEL), the second jet is planned to be used for laser wakefield acceleration experiments, exploring the linear regime. In this latter application, well-tailored and non-symmetric density distributions produced by a supersonic shock front generated by a razor blade inserted laterally to the gas flow, which breaks cylindrical symmetry, need to be characterized.