A team of researchers from the California Institute of Technology (CalTech) have reported the ability to transform physical materials using only the power of light. Unlike previous, more limited methods, this new approach dramatically reduces the absorption of waste heat, allowing the undamaged material to return to its original form.
BACKGROUND: PREVIOUS METHODS AND HEAT ABSORPTION
In movies and TV, characters working in top secret facilities can often turn the glass walls of a room opaque with the flip of a switch, providing the needed privacy for hatching their nefarious plans. In real life, the ability to transform materials using light does currently exist, but with a wide range of limitations. At the top of that list is the excess heat absorbed by the transformed material, which can often lead to permanent damage.
Now, the team from CalTech shows that a new approach seems to address those issues, potentially issuing in a new age of advanced materials science.
ANALYSIS: LET THERE BE LIGHT BUT NOT HEAT
In the study published in the journal Nature, CalTech Physics Professor David Hsieh and a team of researchers led by the study’s lead author Junyi Shan, a graduate student, have shown that they can successfully sculpt the structure of materials using powerful lasers that would typically cause heat damage.
“The lasers required for these experiments are very powerful so it’s hard to not heat up and damage the materials,” said Shan in the press release announcing the breakthrough approach. “On the one hand, we want the material to be subjected to very intense laser light. On the other hand, we don’t want the material to absorb any of that light at all.”
To solve this problem, which has often stymied others in this field of research, Shan, Hsieh and the CalTech team zeroed in on the perfect material, a semiconductor called manganese phosphor trisulphide. This material is noted for its ability to absorb only a very tiny amount of light energy across a wide range of frequencies.
Next, the team found the ideal frequency for their laser, what Shan referred to as a “sweet spot,” where the targeted material undergoes a dramatic structural change, including from opaque to transparent forms, without the absorption of damaging levels of heat energy.
As the press release notes, “the material shifted from a highly opaque state, for certain colors of light, to becoming highly transparent.”
Furthermore, as soon as the laser light was turned off, the material returned to its previous, opaque state without any signs of heat damage. This, the team explains, is because the material’s low level of heat absorption combined with the laser’s magic frequency keeps the targeted material from undergoing a change at the atomic level.
“It’s as if you have a boat, and then a big wave comes along and vigorously rocks the boat up and down without causing any of the passengers to fall down,” explained Hsieh. “Our laser is vigorously rocking the energy levels of the material, and that alters the materials’ properties, but the electrons stay put.”
OUTLOOK: A NEW TOOL FOR MATERIALS SCIENTISTS
The project’s researchers point out that their work is built on previous research done by CalTech alumnus John H. Shirley all the way back to the 1960s. And, they say, their new results match perfectly with Shirley’s predictions, meaning they may have finally delivered on the promise of that early work, while simultaneously offering a whole new set of tools for present day materials scientists.
“In principle, this method can change optical, magnetic and many other properties of materials,” explained Shan. “This is an alternative way of doing materials science. Rather than making new materials to realize different properties, we can take just one material and ultimately give it a broad range of useful properties.”
Follow and connect with author Christopher Plain on Twitter: @plain_fiction