We don’t often have experimental JPhysB Images of the Week, but this week we’ve chosen a great image that gives us a close up look at what is really going on in an experiment. The image below is from a paper by U Zastrau et al in which they assess XUV spectroscopy of hydrogen to show the behaviour of electrons via bremmstrahlung. They show that bremmstrahlung spectroscopy can be used to determine the density and temperature fof free electrons in an evolving plasma on very short timescales (in the order of picoseconds). This timescale is important, because liquid gas jets such as the ones used in the experiment quickly solidify and fragment, at which point spectroscopy becomes difficult.
This image shows a stream of liquid hydrogen being expelled from a cold nozzle through which it has been injected out into a vacuum chamber. The liquid is produced by cooling and compressing hydrogen gas, passing it thorugh a very small point to force it into liquid form. Laser pulses from the FLASH Free-electron laser experiment at DESY are focussed onto a spot in the vacuum chamber where they heat the stream of liquid hydrogen to the point that a plasma is formed which releases radiation. A spectrograph records the spectrum from which information about the behaviour of electrons within the plasma can be inferred.
- Ultrafast electron kinetics in short pulse laser-driven dense hydrogen
- Special Issue on Transient plasmas
- Special Issue on the Frontiers of Free-electron laser science I & II
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Front Image and article image: The liquid hydrogen jet operational in high vacuum, as viewed from a long-range microscope outside the vacuum chamber, from U Zastrau et al 2015 J. Phys. B: At. Mol. Opt. Phys. 48 224004