Plasma & Gas density measurement

Introduction

STRAIGHTFORWARD & HIGH SENSITIVITY DIAGNOSIS | using high resolution phase imaging


SID4 Density is a straightforward and highly sensitive solution for neutral gas and plasma density measurement. It relies on an direct phase shift measurement with our ultra high resolution wavefront sensor, the SID4 HR.


Acknowledgments:

The works on plasma were pioneered at LOASIS, LBNL, which is now known as BELLA (Berkeley Lab Laser Accelerator) Center. The solution results from a fruitful collaboration between SourceLab and Phasics. SourceLab has brought its top-level know-how in laser-plasma interaction experiments and Phasics its strong expertise in phase measurement and analysis.

For

  • For plasma source designers
      • Homogeneity assessment
      • Gas Nozzle optimization

For plasma researchers

  • Plasma density imaging
  • Evolution study, even at the very early stages of creation

Achievements

PLASMA IONIZATION FRONT
Measurement at early creation stages


Plasma-ionization-front

Plasma produced in a 1.1×1020 cm-3 He gas jet

PLASMA DENSITY MEASUREMENT
Using high resolution wavefront sensing


Plasma-density-measurement

Courtesy of LOA

GAS DENSITY
for any axisymmetric monoatomic gas jet


  • high accuracy, from 2 to 300 bars

 
gas-density-measurement

Courtesy of LOA

Introduction

Density is determined by measuring the phase shift induced by the plasma or the gas in a probe beam when it propagates through it. This phase shift is measured with our high resolution wavefront sensor, the SID4 HR. It is related to the plasma (or gas jet) refractive index change. Reverse Abel transform is then used to retrieve the density map. Phasics sensor high spatial resolution (300×400 measurement points) and high sensitivity (<2nm phase shift) ensure reliable density calculations.

Set Up

► As a common-path interferometer, Phasics wavefront sensor directly measures the induced phase shift with no reference arm. Consequently the set-up is very compact and easy to align.
 
► The probe source can be a simple halogen or LED source, as well as a laser beam leakage, as the sensor is achromatic. The solution is cost-effective and versatile.

Advantages

ONE SHOT MEASUREMENT
No scanning


  • Instantaneous image
  • Compatible with femtoseconds laser
  • Small footprint

VERY LOW NOISE
8x lower than Mach-Zender interferometer*


  • Accurate measurement, even at low gas pressure (2 – 300 bars)

*READ MORE

HIGH SHOT-TO-SHOT REPEATABILITY
High resolution & high sensitivity


  • Efficient comparison and gas homogeneity (nozzle selection, laser pulse illumination…)
  • fs-flash measurements to observe how plasma expands at very early stages

STRAIGHTFORWARD SET-UP
No reference arm


  • Easy alignment
  • Compatible with any sources
  • Small footprint
  • Insensitive to vibrations

Comparisons to other techniques

The solution overcomes the classical Mach-Zender interferometer (MZI) limitations by offering compactness, very low measurement noise and compatibility with ultrashort probes.

High Resolution Wavefront Sensor for Plasma & gas density measurement

Scientific publications

American Institute of Physics

DOI: 10.1063/1.3360889

Wavefront-sensor-based electron density measurements for laser-plasma accelerators

Application Note

Plasma density measurement with a common-path interferometric technique

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