Driving down the Junipero Serra Freeway in Palo Alto, California, one comes upon an unusual site – a two-mile long white building that looks like something straight out of Star Trek. And actually, the structure houses a device that isn’t too far off from that futuristic fantasy.
The Stanford Linear Accelerator was founded in 1962 and – for a time – was home to the most powerful nuclear accelerator in the world and still the longest. The device ramped up electrons and their opposite partner the positron to nearly the speed of light before smashing them together. It was some of the first forays into the most basic building blocks of the universe.
But 50 years passed, and today the Tevatron at Fermilab and the Large Hadron Colider at CERN are the kings of the high energy physics world. Being out-powered and in danger of becoming irrelevant, Stanford had to find a different way to utilize the machine and thus the Linac Coherent Light Source (LCLS) was born.
When electrons traveling at high speeds are forced to wiggle back and forth by a magnetic field, they give off x-rays. If you get them going fast enough, wiggle a bunch of them at the same time and make sure it’s done at ridiculously high frequencies, you get an x-ray laser. Scientists take these x-ray laser pulses and shine them on microscopic objects like proteins, molecules and such. When the laser hits the sample, the x-rays bounce off of it in all different directions. By retracing the paths of those x-rays, the researchers can form a “picture” or an “image” of the object.
What makes this sort of process so interesting, however, isn’t just the minuscule objects that are imaged; it’s how fast the pictures can be taken. The frequency between laser pulses is between just 1 and 100 femtoseconds long.
I know, I know – you have no clue what the hell a femtosecond is. Let me help.
It takes about 100 femtoseconds for a shock wave to propagate through a single atom. No? Okay, light – the absolute fastest thing in the universe, the same light that can circle the Earth 7.5 times in a single second – can travel only one millimeter in three femtoseconds.
The only thing faster is the plummet of LeBron James’ popularity.
Blasting proteins or other organic molecules with such an intense light immediately destroys the sample. However, the laser is so fast that it can snap hundreds of images before the sample even has time to react and realize it has been destroyed. I mean it can even take a series of images that shows chemical reactions in progress.
So where am I going with this?
Well, lasers like this are extremely useful machines and scientists fight over who gets to use it for the next experiment. And unfortunately, not everybody has a two-mile-long linear accelerator in their back yard that can make their own x-ray laser. Nor do they have $900 million to build a different sort of synchrotron light source like Brookhaven National Laboratory is in the process of as I type.
But soon scientists may not need it anymore.
In a paper recently published in Nature Physics, researchers at the University of Michigan in collaboration with the Imperial College of London and Instiuto Superior Technico Libson have demonstrated the feasibility of a machine that can make these same probing lasers but fit on your kitchen table.
Using a high power laser beam in Ann Arbor named HERCULES, the team shot a beam into a jet of helium gas to create a tiny column of ionized (atoms stripped of electrons) helium plasma (matter so hot that molecular bonds break apart.) In this plasma, the laser pulse creates an inner bubble of positively charged helium ions surrounded by a sheath of negatively charged electrons.
Due to this charge separation, the plasma bubble has powerful electric fields that both accelerate some of the electrons in the plasma to form an energetic beam and also make the beam ‘wiggle’. These, in turn, make the same x-rays of comparable power on comparable time scales as the mammoth Stanford Linear Accelerator.
It is going to take quite a while to figure out the logistics of what a final machine would look like and exactly how it would function, and even more time to begin producing such machines. And it’s not like lasers as powerful as HERCULES are a dime a dozen. However, in the long run, it is very exciting news. Researchers wanting to detail how proteins interact with each other or how antibodies fight viruses will be able to do so without having to wait their turn at a big national laboratory and the scientific information will flow like never before.