How hot plasma breathes
doi:10.1038/nindia.2010.133 Published online 29 September 2010
Extremely short and high-intensity laser pulses are generally used to ionize a solid and create hot and dense plasma. A team of researchers has now used similar but weaker laser pulse to probe plasma, providing the first glimpse of hot, ultrarapid plasma motion.
The research is important for a wide variety of applications, ranging from the optimization of X-ray and particle emissions to achieving laser fusion.
It is difficult to track plasma as it moves on ultrafast timescales. The researchers used femtosecond pump–probe Doppler spectroscopy to map the dynamics of hot plasma.
They employed a high-intensity 30 fs pump laser pulse to heat polished glass coated with a thin layer of aluminium. The glass yielded a hot and dense plasma. A small fraction of the pump laser was split off and used as a probe to monitor the plasma motion.
The team observed that the plasma critical surface was initially pushed inwards under the influence of a compression wave launched by the pump pulse, giving a red shift in the reflected probe light. The compression wave then moved deeper and the plasma moved away from the target, which induced a blue shift.
"Tracking plasma motion is important to understand how laser light interacts with plasma and leads to the generation of energetic electrons," says lead researcher G. Ravindra Kumar. It also sheds light on the generation of ultrastrong magnetic fields and electromagnetic emissions in the plasma.
The authors of this work are from: Tata Institute of Fundamental Research, Mumbai, India; Department of Physics, University of York, York, United Kingdom; and Central Laser Facility, Rutherford Appleton Laboratory, Oxfordshire, United Kingdom.