In the first half of the 20th century, ability to observe events at a scale of microseconds—millionths of a second—was considered a remarkable achievement and in the second half the research passed through nanoseconds (billionths of a second) and picoseconds (trillionths). In 2000, researchers could easily reach into the realm of femtoseconds—quadrillionths (or millionths of a billionth) of a second, the timescale of motions within molecules.
Today top-shelf technologies are beginning to make it possible to observe events that last less than 100 attoseconds, or quintillionths of a second.
The ability to observe events on such timescales is important for basic physics—to understand how atoms move within molecules—as well as for engineering semiconductor devices, and for understanding basic biological processes at the molecular level.
But physicists and engineers are interested in pushing these limits even further to the attosecond and ultimately zeptosecond (sixtrillionths of a second) range to understand the movements of electrons, and eventually those of subatomic particles.
High-energy X-ray pulses with femtosecond duration could make it possible to obtain detailed images, and ultimately movies, of the dynamics of complex protein molecules, Kaertner says—something that can’t be done with existing techniques, and could be of great interest for biomedical research. But high-energy X-ray pulses that can probe these complex structures also destroy them in the process, so the pulse has to be so quick that the image can be obtained before the pieces fly apart.
“If the pulse is short enough, all the X-rays diffract from the protein before it is destroyed,” Kaertner says. This is called diffraction before destruction. “It’s a hot field at the moment,” he adds.
Beyond basic research, femtosecond lasers have many practical applications as well. The most common are in the micromachining of materials and in Lasik eye surgery—which was enabled by the development of robust femtosecond pulsed lasers. These extremely short pulses made it possible to deposit high energy to destroy material such as tissue on a tiny spatial scale, without having enough time for the energy to diffuse and damage surrounding tissue, Kaertner says.
So, just how short is a femtosecond? One way to think of it, Kaertner says, is in terms of how far light can move in a given amount of time. Light travels about 300,000 kilometers (or 186,000 miles) in one second. That means it goes about 30 cm—about one foot—in one nanosecond. In one femtosecond, light travels just 300 nm—about the size of the biggest particle that can pass through a HEPA filter, and just slightly larger than the smallest bacteria.
Another way of thinking about the length of a femtosecond is this: One femtosecond is to one second as one second is to about 32 million years.
As the technology continues to march forward, there may be more talk about zeptoseconds and yoctoseconds—or, going in the other direction, things such as zettabytes of data or yottawatts of power—coming up in our future.
- Shortest laser pulse lasts just 67 attoseconds (whitenewsnow.com)
- Femtosecond lasers non-invasively destroys brain and other cancer tumors (nextbigfuture.com)