Phasics Plasma & Gas Density Measurement

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.

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)

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 source
• 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.