Plasma & Gas Jet Metrology

Straightforward and high-sensitivity diagnostic tool using high resolution phase imaging

The SID4 Density is a straightforward and extremely sensitive solution for neutral gas and plasma density measurement. It relies on a direct phase-shift measurement with our high-resolution wavefront sensor, the SID4 HR. The Phasics Density module addresses plasma and gas density measurement challenges for engineers and researchers working in plasma source design, laser-wake field acceleration (LWFA), and high-field sciences experiments. 

The works on plasma were pioneered at LOASIS, LBNL, which is now known as BELLA (Berkeley Lab Laser Accelerator) Center. The solution resulted 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.

  • ▽ Neutral gas particle density measurement setup

    Setup showing neutral gas particle density measurement setup with SID4 HR wavefront sensor

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

    As a common-path interferometer, the Phasics wavefront sensor directly measures the induced phase shift with no reference arm. Consequently, the setup 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.

  • ▽ Plasma electron density measurement setup

    Setup showing plasma electron density measurement setup with SID4 HR wavefront sensor

    For plasma density measurement, the principle and implementation are similar as for the gas density. The only difference is that the probe beam must be synchronized with the drive laser. To do so, it  is easy to use a small portion of the drive laser via a mirror leakage. A delay line can be used to study plasma dynamics and the probe can be frequency doubled to increase sensitivity.


Measurements Examples

Electron density map of a helium gas jet measured  with a visible SID4-HR wavefront sensor

Plasma density

Measurement map of density produced by an Argon gas jet measured  with QWLSI technology

Gas density

GIF with 3 images of the plasma electron density with 3differnent  delays between the pump and the probe

Plasma ionization front


Single-shot measurement

  • No scanning
  • Live phase-shift calculation
  • Intensity images 

Very low noise 

  • Phase shift sensitivity <2nm 
  • 8x lower than Mach-Zehnder 
  • Accurate measurement

Small footprint

  • Easy to align 
  • Not sensitive to environment
  • Easy to integrate in the optical setup 


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