Cognitive Daily

Researchers have developed a new method of creating laser beams which they believe may pave the way for practical laser X-rays:

Most of today’s X-ray lasers require so much power that they rely on fusion laser facilities the size of football stadiums, making their use impractical.

“We’ve come up with a good end run around the requirement for a monstrous power source,” research Henry Kapteyn said.

Once this hurdle is overcome, the researchers say, a small, inexpensive X-ray laser becomes practical. Instead of shadowy, fuzzy X-ray images, X-rays could become incredibly precise — perhaps even at the nano-scale. I don’t know much about lasers, so I’m wondering if readers (or fellow ScienceBloggers — Chad? Rob?) could help me out with answers to a few questions:

1. It looks like the research here just describes the principle; there’s no working prototype. How long does it generally take for this sort of research to be applied?

2. My understanding is that a laser isn’t necessarily more intense than other light sources — it’s just that the light waves are better synchronized. So is it possible that a lower intensity light source could be used for laser X-rays than traditional X-rays, thus making them safer? Or would the opposite be true — would laser X-rays have to be higher-intensity, and less safe than the traditional variety?

3. X-rays work in real time, right? So we could have not only very high-res images, but also movies. Could it be possible, then, that what we have here might be something like the holy grail of neuroscience — a device that could measure brain activity both at high resolution and in real time?

4. On the other hand, even at this resolution, maybe the device would still not be able to measure brain activity. After all, we’re talking about things happening at the molecular level. Perhaps the X-ray laser still couldn’t “see” individual neurons firing. Or is there some way people could be prepared in advance — perhaps by swallowing or being injected with some type of marker visible by X-rays?

In any case, the device looks to have important applications, especially in the detection of very small tumors. I look forward to seeing the images produced by the first working laser X-rays.


  1. #1 NJ
    February 27, 2007

    I suspect that they won’t be X-ray images that you’re familiar with. They would probably be used in crystallography to make the phase problem go away, i.e. they would be producing holographic images of atoms in crystals in order to solve the crystal structures.

  2. #2 Mustafa Mond, FCD
    February 27, 2007

    I took a look at the ScienceDaily press release, and it is very distorted. I haven’t seen the original paper yet, so it could be bad science reporting rather than bad science.

    Macromolecular crystallography requires “hard X-rays”; wavelengths of ~ 2 Angstroms or shorter. The press release specifically states they are not yet in that regime. It could instead be used for imaging of materials science samples (semiconductors, nanomaterials) or biological research specimens like bone or single cells. The radiation dose to do so would probably kill the cells, so this would be research rather than medical use.

    For example, the X-rays we get in the hospital are limited by spatial resolution. They can’t detect really small cancers because the X-ray source in your doctor’s office is like a light bulb, not like a laser. If you had a bright, laser-like X-ray beam, you could image with far higher resolution.”

    This is really dumb. Resolution is limited by wavelength, not brightness. The way to compensate for lack of brightness is to take a longer exposure. The wavelengths used for medical X-rays are even shorter than those used for crystallography, because they need to penetrate tissue. Increasing exposure would require careful consideration of the diagnostic benefit vs. the tissue damage, so it would not likely pay off to search for ever smaller tumors with X-rays. Something less damaging, like ultrasound or MRI would be a better bet. Moreover, medical X-rays do not require coherence, which is the selling point of a laser.

  3. #3 Mustafa Mond, FCD
    February 27, 2007

    X-rays work in real time, right? So we could have not only very high-res images, but also movies.

    Sure, X-rays work in real time. The limiting factor to this would be the detector. The current “state of the art” are charge-coupled devices (CCDs), like in a digital camera. By pushing the technology you could probably get it pretty close to video speed.

    As for using it on a living brain, the bit about tissue damage would be highly relevant, and also the lack of penetrating power of the “soft X-rays” they are working with. No way would I let someone fry my brain with an X-ray laser.

  4. #4 Ponderer of Things
    February 27, 2007

    in xray imaging (radiology) resolution is limited by many factors, including size of pixel/grain size of the film, but also how parallel x-rays are (otherwise x-ray transmission from different angles will overlap, making objects “blurry”).
    Higher brightness (more precisely, higher emittance, keeping flux constant) can help reduce this effect, ultimately down to diffraction limit.

    Coherent x-ray sources (x-ray lasers) are more exciting for other reasons – one could do tricks like phase contrast imaging (using phase, rather than intensity), which can be used to differentiate soft tissues of similar adsoption contrast. In far-field diffraction regime one could use holography, or lens-less imaging (a technique based on phase retrieval that can provide full 3D images of illuminated objects, ultimately down to diffraction limit).

    But those techniques do require incredible brightness such as new free electron laser facility at Stanford (LCLS) – you can use this to image hard-to-crystallize biological molecules, but not the brain activity.

    For brain activity, I would imagine phase constrast imaging is the most exciting development, and probably could be used for things you mention, including single neuron firing off.

    High energy of x-ray photons doesn’t mean that the overall dose (number of photons per second times energy of individual photon) has to be high. The dose could be actually quite low for these type of measurements.

    Another great advantage of highly coherent x-ray sources is that you can focus x-rays down to nanometer-sized spots. Radiation damage then becomes a big issue, but in principle you could imagine doing all kinds of microscopies with spot size well below wavelength of visible light, plus x-rays can of course penetrate much deeper into the sample than electrons or visible photons (for many non-transparent materials), and there is plenty of resonance edges in x-ray energy spectrum to use fluorescence as a chemical marker (to see for example where potassium or zinc is in the cell).

    But I suspect that top science is going to be done at big facilities such as LCLS. Table top x-ray lasers (or “tiny” synchrotrons that can fit in the room developed commercially) have a long way to go before getting anywhere close to the flux/emittance parameters of the bigger machines.

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