CETAL-PW | Research | Plasma diagnostics

It is well known that when a high-intensity laser beam interacts with matter, it induces ionization and particle acceleration. Electron, proton and ion beams arise from the primary ionization and acceleration process, while neutrons and very intense gamma flux are generated in secondary processes as bremsstrahlung and nuclear reactions.
The investigation of laser-based acceleration process and of the radiations generated in this way, implies a complete diagnostics of plasma and accelerating structures generated by high power laser pulses. Detailed knowledge about spatial and temporal distribution of plasma parameters helps to predict spatial and temporal characteristics of the accelerated beams.

Plasma diagnosis methods:

Folded wave and interferometry
The transversal interferometry technique is based on a folded-wave configuration where the probe beam passing through the plasma is split in two beams of equal intensity. By spatially inverting the beam in one arm before recombining the two beams, the area of each laser beam unaffected by the plasma interfered with the affected area of the other. Later, the plasma density is recover from the interferograms by fringe pattern analysis and electron density map is deduced from the phase map via its relation to the refractive index applying an Abel inversion.

Wave-front sensor based diagnosis
In the wave-front sensor measurement, only one arm of a nonperturbative probe laser beam is required, the wavefront sensor measuring directly the phase front curvature of an incoming laser beam. The data processing follow the same path with as the interferometric method.

Single shot investigation based on chirped pulse
In the single-shot investigation of the plasma, single shot temporal characterization of the plasma using an additional beam synchronized with the main laser beam. Principal parameter of the ionized medium which can be investigated using a light pulses is the refractive index which is directly related to the electrons density localized at the interaction between the main pulse and the molecules of a gas.