Laser window into the universe
doi:10.1038/nindia.2012.94 Published online 26 June 2012
Researchers have created extremely hot laser-induced plasmas with strong turbulent magnetic fields by irradiating a solid target with extremely short infrared pulses. Studying such hot plasmas with visible laser probe beams could be helpful for simulating ultrahigh-pressure intra-planetary matter and developing tools to model astrophysical bodies such as stars.
The movement of electrons through hot dense matter at nearly the speed of light is a complex process that is still poorly understood. In addition, researchers have yet to investigate the generation of turbulent magnetic fields on a micrometer spatial scale and over a picosecond timescale.
To investigate such short-lived turbulent magnetic fields and electron jets, the researchers irradiated an optically polished aluminium-coated BK-7 glass target with 30 fs infrared pump pulses in a vacuum chamber. The incident pulses interacted only with the aluminium coating to create a hot, electron-rich plasma-on-aluminium layer. They then used a weak 80 fs probe pulse to sample the plasma at different time delays after irradiation.
The researchers used a microscope coupled to a CCD camera to view the spatial overlap between the pump and probe pulses. The pump laser produced hot energetic electrons at the critical-density surface — the area in the plasma that reflects the pump pulse. These electrons propagated inwards and the resulting space–charge and induction field generated a return shielding current of the background cold electrons. The reflected probe pulse was useful for measuring magnetic fields larger than the pump focal spot at the target. The observed magnetic field was cylindrically asymmetric.
The magnetic field at the critical surface of the probe increased from 0 to 63 megagauss over a period of 3.2 ps, after which it decreased. The researchers observed filamentary magnetic structures at the critical surface up to 7.0 ps after pump irradiation.
The authors of this research are from: Tata Institute of Fundamental Research, Mumbai, and Institute for Plasma Research, Bhat, Gandhinagar, India; Beijing National Laboratory of Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing and Laboratory for Laser Plasmas (Ministry of Education) and Department of Physics, Shanghai Jiao Tong University, Shanghai, China.
- Mondal, S. et al. Direct observation of turbulent magnetic fields in hot, dense laser produced plasmas. P. Natl. Acad. Sci. USA 109, 8011-8015 (2012) | Article |