Laser technology has been synonymous with the “cutting edge” of science since its invention in the 1950s. The concept was first theorized by Albert Einstein in 1917, and has been rapidly advancing ever since.
That’s not to mention the intrinsic link between lasers and science fiction. In virtually all futuristic fiction, lasers make an appearance as the weapon of choice.
After all, hypothetically, why carry around bullets when you can have an unlimited supply of laser pulses? Coupled with this are the shields that these futuristic warriors have. Shiny, fluid-like membranes are shown encompassing a ship from which laser blasts simply bounce right off.
The physics here are actually reasonably sound; after all, mirrors reflect optical lasers. What if there could be a device that, rather than reflecting the light, simply absorbed and destroyed it? New research done at Yale University shows that such technology, in fact, might not be science fiction.
In an article titled “Time Revered Lasing and Interferometric Control of Absorption” published last week in Science, a team of physicists described the theoretical and experimental proof of a device. The team named such a device a “coherent perfect absorber” (CPA).
The idea was first proposed by A. Douglas Stone, one of the co-authors of the new paper.
“The idea of time-reversed lasing came from [him] about two years ago when he was working on the theory of complex laser,” co-author Hui Cao wrote in an email to The News-Letter. “I participated in many discussions while his group was developing the theory of time-reversed laser . . . [and] started working on the experiments right after the theory was developed.”
The simplest manifestation of a CPA involves a single laser beam that passes through a cavity and then hits a mirror, reflecting back upon itself.
When tuned correctly, the original laser beam and the reflected beam interfere destructively. The two beams essentially line up and cancel each other out, causing the laser’s energy to be absorbed by the CPA.
A more complex version of the system, a two-channel CPA involves a network of mirrors and beam splitters in which a silicon wafer about a 10th of a millimeter thick is placed in the beam.
Again, once the phase of the light is adjusted, the silicon wafer can absorb the laser beam and turn its energy into another form such as heat or electrical current. Overall, the prototype was able to absorb over 99 percent of the incident light.
To get to this point though, the researchers had to “ensure the spatial and temporal coherence of two beams that are incident on the silicon wafer from the opposite sides, and also improve the spectral resolution of our detector to see large modulation of output intensity when varying the relative phase of the two beams,” Cao wrote.
“This is a very intriguing result,” Daniel Reich, chair of the department of physics and astronomy at Hopkins wrote in an email to The News-Letter. “From the fundamental physics viewpoint, it is a very elegant demonstration of time reversal symmetry in coherent optics.”
One potential use for this technology is in the field of high-speed computing. The computers of tomorrow will use optical instead of electrical signals.
“As the authors suggest,” continued Reich, “[this research] also holds out the potential for applications in optical communications technology, particularly if the effect can be made tunable so that it can work at multiple frequencies.”
Other potential applications for the anti-laser in the field of biology include detection systems for pollutants as well as surgical devices that can focus energy to be absorbed at a specified depth under the skin. This could prove a very useful property in targeting a specific area of the body in medical imaging.
