Biomedical engineer Lihong Wang and his research lab at Washington University in St. Louis have invented or discovered a whole bunch of high-tech imaging techniques, with sophisticated names like functional photoacoustic tomography, dark-field confocal photoacoustic microscopy and time-reversed ultrasonically encoded optical focusing.
So it probably won’t come as a surprise that the new camera Wang’s team has developed is far from ordinary. But he describes the accomplishment in a very straightforward manner: “For the first time, humans can literally see light pulses traveling in space at the speed of light," he said.
This video captured by Wang’s new imaging system shows a laser pulse propagating in air and being reflected from a mirror. The movie is slowed down 10 billion times to make it visible to the human eye. (Credit - Lihong Wang, Washington University)
One hundred billion pictures a second
The speed of light is almost 300-million meters per second (299,792,458 m/s). Going that fast, it would take you about one second to go all the way around the world, seven and a half times.
“Based on Einstein’s Theory of Relativity, any mass or energy can propagate only up to the speed of light," Wong explained. "So we’re literally talking about the fastest phenomenon in the world.”
So how do you take a picture of a light pulse moving at the speed of light? Wang says you start with something called a streak camera, a specialized device that allows him to convert time into space.
Converting time into space is a simple concept for physicists, at least. “We convert light particles, or photons, into electrons, then pull the electrons, really hard, at different rates, depending on the time of arrival. So the time of arrival will be converted into different vertical positions," he said.
The details only get more complicated, but here’s the main point: Wang’s new technology improves on previous ultrafast cameras in two important ways.
Up until now, streak cameras could only take a one-dimensional snapshot ― think of it as looking through a vertical slit and trying to take a picture of something flying by really fast.
And the fastest cameras had to have an external light source to work.
Wang’s technique doesn’t need special lighting, and it produces 2-dimensional images ― more like regular photographs ― but at a rate of one every 10 trillionths of a second.
A major development
Dartmouth biomedical engineer Brian Pogue wasn’t involved with developing the new imaging system ― but he reviewed it for the journal Nature, where Wang’s research is published.
“Anytime that you create a system that images a thousand times faster than what exists today, that’s a big deal," said Pogue.
Pogue says this new way of visualizing the movement of light could lead to major scientific breakthroughs in fields like physics… and military defense, such as optical cloaking, a term familiar to fans of the American TV show Star Trek.
In science fiction, cloaking is a technology that can make an object ― like a spaceship ― seem to disappear. Pogue says it’s something the military would like to be able to do in real life.
“There’s a lot of interest in getting light to bend around objects, so it sort of looks like you’re seeing through them," he said.
He says Wang’s new system would allow researchers to image the light as it bends ― something they haven’t been able to do before, and that could help make optical cloaking a reality.
Lihong Wang imagines other uses for the new camera, from molecular biology to astronomy ― really any field where ultrafast imaging could lead to new discoveries.