Real-Time Tomography of Gas-Jets with a Wollaston Interferometer

Abstract

A tomographic gas-density diagnostic using a Single-Beam Wollaston Interferometer able to characterize 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 Maximization 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 characterized: a kHz, piezo-driven jet for lower densities and a solenoid valve-based jet producing higher densities. While the first jet is used for free electron laser photon beam characterization, the second jet is used in laser wake field acceleration experiments. 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.

Optical diagnostics for density measurement in high-quality laser-plasma electron accelerators

“…For the simplest case of cylindrically symmetric samples the well-known Abel inversion method is used, which allows one to extract the actual value of the radially dependent density from line-integrated measurements along several chords [17, 18] . In the case of non-cylindrically symmetric targets, multiple measurements along different lines of sight are necessary to implement a 3D tomographic reconstruction procedure [19, 20] . Finally, in the case of homogeneous samples, such as uniformly filled gas cells, the density is actually given by the average density measured by means of interferometry [21] .…”

Supersonic gas jet stabilization in laser–plasma acceleration

“…In this case, a more stable gas target prepared for laser irradiating can be expected. Here, the numerical calculations are proved by the experimental measurements via the Mach-Zehnder interferometric method [44][45][46] .…”

AnaBHEL (Analog Black Hole Evaporation via Lasers) Experiment: Concept, Design, and Status

“…An electrically controlled valve is placed between the nozzle and the tank to control the flow. There are several techniques to quantitatively characterize the density of a supersonic gas jet, including interferometry and shadowgraphy [62][63][64][65], tomography [62,66,67], planar laser-induced fluorescence (PLIF) [60,68,69], Schlieren optics [70,71] (more references can be found in [71]). As the first step, we built a Schlieren imaging system in the lab for the jet characterization.…”