The X-Ray laser was a main weapon envisioned for the Reagan administration's Strategic Defense Initiative (SDI).  The descendants of that technology are used to image nano-scale structures the size of individual proteins.  This is a prime example of how science is not a moral pursuit. Science simply reveals tools for our use. 


In the early 1980's, Ronald Reagan was president and had been talking tough when it came to the Soviet Union. After reviewing our operational plans and facilities for fighting a nuclear war, he came to a grim conclusion.   We could accurately track inbound missiles, bombers, and subs. We could tell where they would strike and when. However, there was nothing we could do to stop them.  The presidents options were to retaliate, or ride out the attack and try to keep the upper hand in a post war world. (With our cities destroyed, what would we have to loose by attacking at that point? While the other guy would have everything to loose. ) 

Edward Teller contacted the president and made him aware of the theoretical possibility that this weapon could shoot down multiple inbound ICBM's.  This artist rendering is typical of the era. 

Click for larger version

The image above comes from a poster I prepared for a class in Laser Physics.  I don't recall the artist, and don't claim to have rendered it myself.  As the poster says only one test of this weapons system was carried out successfully.

The basic physics of the X-ray laser are the same as for a normal laser. Energy bonds within a system are excited to a higher energy state.  Then, once that high energy state reaches a certain saturation, it releases that energy as a single wavelength pulse of energy.  The classic visible light LASER involves a medium such as ruby and a pumping source such as  LEDs.  The X-Ray lasers of SDI involved a metal crystal which would be stimulated by the intense radiation from an atomic bomb blast and emit X-rays.   In the process the device destroys itself.  One design called for multiple laser emitters powered by one nuclear device. Each emitter would target a missile, and they would all simultaneously fire when the device detonated. It was said at the time that a device the size of a large office desk could take out a dozen missiles.

There was only one underground test of this concept which had possibly successful results.  The other possibility is that the sensor which detected the X-ray emission was faulty.  That sensor was destroyed in the test so this possibility could not be checked. 

X-ray Free Electron Lasers

In the last decade the development of X-Ray lasers has accelerated with the introduction of high energy free electron lasers.  The way these work is quite different from the SDI era devices.  The current technology uses a linear electron accelerator and a long set of alternating magnets called an undulator.  The rapid accelerations of the electrons release radiation at a precise X-ray frequency which depends on the spacing of the magnets in the undulator.  As this image illustrates. 

An illustration of an FEL undulator (Credit Wikimedia foundation) 
As the electrons pass by each magnet radiation is released.  To get a useful amplification the undulator has to be quite long. 

The most powerful operating facility which uses this technique to generate an X-ray laser is in Hamburg Germany. A major new facility is under construction the European XFEL.

Uses of this technology.  

What good is this technology?   It is of course used for imaging, but you would not want to put your possibly broken leg in front of it! 

These lasers have the intensity to make high resolution images of tiny structures.  Things like proteins, molecules, nanomachines etc can be destructively imaged by this technique. 

This image, taken from the same poster  illustrates the process. The X-ray laser beam, in red, enters from the left.  The beam shines on a tiny (twenty micrometer) spot on a known sample. The sample is only nanometers thick. The beam scans the image onto a specially made mirror. The angle the mirror is chosen to reflect the x-rays which can happen at certain angles.

The image produced on the charge couple device (CCD) which is sensitive to X-rays is actually an interference pattern.  At first glance this pattern does not contain any useful information.  However with enough processing power and a really complicated fourier transform the image can be reconstructed. 

This last panel shows a comparison of the known image to the reconstructed image.  The level of detail is quite high.   

The applications of this technology are bounded only by our imaginations.  Imagine that  the surface of a deadly virus like Ebola or HIV could be imaged in high detail. We could design pharmaceuticals which would interface more precisely with these  bugs. Perhaps the European XFEL will be able to do this.  The possibilities are endless. 

A technology devised for war can now be used for peace and progress.