Faster lasers could reveal better data storage

"Even if there is a laser faster than a femtosecond laser, there will be a limit as to how fast this transition can occur and information can be recorded, just because of the physics of these phase-change materials," says Giovanni Vanacore. "It's something that cannot be solved technologically—it's fundamental." (Credit: "DVDs" via Shutterstock)

DVDs and Blu-ray disks contain so-called phase-change materials that morph from one atomic state to another after being struck with pulses of laser light, with data “recorded” in those two atomic states.

Using ultrafast laser pulses that speed up the data recording process, researchers adopted a novel technique, ultrafast electron crystallography (UEC), to visualize directly in four dimensions the changing atomic configurations of the materials undergoing the phase changes.


By shedding light on the fundamental physical processes involved in data storage, the work may lead to better, faster computer memory systems with larger storage capacity. The research, done in the laboratory of Ahmed Zewail, professor of chemistry and of physics at Caltech, appears online in ACS Nano.

Recording data in 0s and 1s


“Today, nanosecond lasers—lasers that pulse light at one-billionth of a second—are used to record information on DVDs and Blu-ray disks, by driving the material from one state to another,” explains Giovanni Vanacore, a postdoctoral scholar and an author of the study. The speed with which data can be recorded is determined both by the speed of the laser—that is, by the duration of each “pulse” of light—and by how fast the material itself can shift from one state to the other.

Thus, with a nanosecond laser, “the fastest you can record information is one information unit, one 0 or 1, every nanosecond,” says Jianbo Hu, a postdoctoral scholar and the first author of the paper. “To go even faster, people have started to use femtosecond lasers, which can potentially record one unit every one millionth of a billionth of a second. We wanted to know what actually happens to the material at this speed and if there is a limit to how fast you can go from one structural phase to another.”

A new limit

To study this, the researchers used their technique, ultrafast electron crystallography. The technique, a new development, allowed researchers to observe directly the transitioning atomic configuration of a prototypical phase-change material, germanium telluride (GeTe), when it is hit by a femtosecond laser pulse.



“Even if there is a laser faster than a femtosecond laser, there will be a limit as to how fast this transition can occur and information can be recorded, just because of the physics of these phase-change materials,” Vanacore says. “It’s something that cannot be solved technologically—it’s fundamental.”

Better data storage








The National Science Foundation and the Air Force Office of Scientific Research supported the work. The research too place in Caltech’s Center for Physical Biology, which is funded by the Gordon and Betty Moore Foundation.

Source: Caltech