First-of-its-Kind Hard X-ray Free-Electron Laser Images Intact Viruses 84
Zothecula writes "In a paper published in the current edition of Nature, an international team of scientists describe how they obtained the world's first single-shot images of intact viruses – a technology that could ultimately lead to moving video of molecules, viruses and live microbes. Another paper by the same team describes how they were also able to successfully utilize a new shortcut for determining the 3D structures of proteins. Both advances were achieved using the world's first hard X-ray free-electron laser – the Linac Coherent Light Source (LCLS) – which scientists hope could revolutionize the study of life."
Link (Score:5, Informative)
Simple answer: No. (Score:4, Informative)
The duration of its individual pulses is incredibly short – a few millionths of a billionth of a second. That’s still long enough to cause its subjects to vaporize , but that doesn’t happen until after their pictures have been snapped.
OK, this was in the second paragraph, but even so...
"Laser", but not really (Score:5, Informative)
I am a physicist-in-training (grad student), and when I first heard of "free electron lasers" I was extremely impressed, because getting electrons into a multi-keV energy state that can lase without atoms involved sounded nearly impossible. Turns out it is, because these are not actually "lasers" the sense of Light Amplification by Stimulated Emission of Radiation. There is no population inversion [wikipedia.org] as in real lasers.
The name of this specific FEL, the "Linac Coherent Light Source", is a much more correct name. They shoot electrons through a wiggler, and as they wiggle they emit coherent photons. Coherency is they key property of laser light, but the name refers to the method of light creation more than the actual output. I don't know why the x-ray community has felt the need to use this misleading name.
Video from Stanford onn LCLS (Score:5, Informative)
Here's a video (animation) from Stanford explaining how the LCLC works.
http://lcls.slac.stanford.edu/AnimationViewLCLS.aspx [stanford.edu]
Re:"Laser", but not really (Score:2, Informative)
Not only that, a Free electron laser (FEL) is only spatially coherent, not temporally coherent. This is a drawback of the "single-pass" method of X-Ray generation in FELs. Essentially, you can compare a FEL to amplified spontaneous emission (ASE) that is common in devices like superluminescent diodes. The bunching of electrons in FELs along the wiggler leads to different bunches that emit temporally coherent X-Rays, but across the entire FEL there are a large number of such bunches resulting in a spectral output that consists of a wide range of x-ray energies with many peaks overlayed on top.
There isn't any temporally coherent X-Ray laser to date. People have proposed using very pure diamond crystals as X-Ray mirrors to set up a feedback cavity to a FEL, thus allowing for true temporal coherence just as in the case of traditional lasers that rely on a feedback cavity to establish temporal coherence. There are also some more esoteric proposals involving using a coherent "seed" laser, to seed the FEL oscillations, but it involves using 500+ order harmonics via non-linear effects.
For the curious (and those with access to Nature) - this is a very nice, informative review on FELs: http://www.nature.com/nphoton/journal/v4/n12/abs/nphoton.2010.239.html
Re:Simple answer: No. (Score:4, Informative)
You mean "normal" X-rays which is defined as the electromagnetic spectrum between 10 and 10,000 pm? As opposed to the backscatter X-rays which could range anywhere in the electromagnetic spectrum between 10 and 10,000 pm? Attenuation (transmission) and backscatter are different techniques for X-ray imaging - but they both still use X-rays. It's like the difference of looking at a stain glass window from the inside or the outside of the church - in both cases it's sunlight that does the illumination.
It does get more complicated when you talk about specific wavelength, intensity, and etc... when you try to measure dosage. But all X-ray methods utilize ionizing radiation which is carcinogenic. Dose may be a very small portion of what you get every day, or in the case of the X-ray laser here, it may be enough to vaporize you.