Transforming Materials With Light – Enabling Windows That Transform Into Mirrors and Super High-Speed Computers


You can see a powerful laser illuminating the material in the cold chamber. Lasers are used to change the transparency of a material. Credits: Caltech / David Hsieh Laboratory

Imagine a window that can easily be transformed into a mirror, or an ultra-fast computer that runs on light instead of electrons. These are just a few of the potential applications that can result from optical engineering, a technique that uses lasers to change material properties quickly and temporarily.

“With these tools, you can convert the electronic properties of a material with the push of a light switch,” said David Hsieh, a professor of physics at the California Institute of Technology. “But the technology has been limited by the problem that lasers generate excessive heat in the material.”

In a new study of NatureHsieh, including lead author and graduate student Junyi Shan, and his team report that they have succeeded in dramatically engraving the properties of a material using a laser without generating excessive heat of damage. increase.

“The lasers needed for these experiments are so powerful that it’s difficult to heat the material to prevent damage,” says Shan. “On the one hand, we want to shine a very strong laser beam on the material. On the other hand, we don’t want the material to absorb that light at all.”

The team has found a “sweet spot” to avoid this, says Shan. There, the frequency of the laser is fine-tuned to significantly change the properties of the material without applying unnecessary heat.

Jun Ishan

Jun Ishan. Credit: Caltech

Scientists also say they have found the ideal material to demonstrate this method. This material is a semiconductor called phosphorus trisulfide, which absorbs only a small amount of light over a wide range of infrared frequencies. In their experiments, Hsieh, Shan, and colleagues used powerful infrared laser pulses, each lasting about 10-13 seconds, to rapidly change the energy of electrons in the material. As a result, the material has moved from a highly opaque state to a highly transparent state for light of a particular color.

More importantly, the process is reversible. When the laser is turned off, the material immediately returns to its original, completely intact state. This is not possible if the material absorbs the laser light and is heated, as it takes a long time to dissipate the heat. The heatless operation used in the new process is known as “coherent optical engineering”.

This method works because light changes the difference in energy levels of electrons in a semiconductor (called the bandgap) without kicking the electrons themselves to different energy levels. This produces heat.

David She

David Shay. Credit: Caltech

“Big waves come in and rock the boat violently up and down without knocking down passengers, as if you were holding a boat,” she explains. “Our laser violently shakes the energy level of the material. It changes the properties of the material, but the electrons remain in place.”

Researchers have previously theorized how this method works. For example, in the 1960s, California Institute of Technology graduate Jon H. Shirley (PhD ’63) presented a mathematical idea on how to solve the electron energy levels of a material in the presence of light. Based on this work, Hsieh’s Caltech team worked with theorists Mengxing Ye and Leon Balents at the University of California, Santa Barbara to calculate the expected effect of laser illumination on manganese trisulfide phosphorus.Theory matched the experiment with “notable” Accuracy, Hsieh says.

The findings may allow other researchers to use light to artificially create materials such as exotic quantum magnets that were otherwise difficult or even impossible to create naturally. It means that.

“In principle, this method can change the optical, magnetic, and many other properties of the material,” says Shan. “This is an alternative way to do materials science. Instead of creating new materials to achieve different properties, use only one material and ultimately give it a wide range of useful properties. I can.”

Reference: “Giant Modulation of Optical Nonlinearity by Floquet Engineering”, Jun-Yi Shan, M. Ye, H. Chu, Sungmin Lee, Je-Geun Park, L. Balents, D. Hsieh, December 8, 2021 Nature..
DOI: 10.1038 / s41586-021-04051-8

This study was funded by the Army Institute. David Andrseal Packard Foundation; National Science Foundation via the Institute of Quantum Information and Materials, California Institute of Technology and the University of California, Santa Barbara. Gordon and Betty Moore Foundation; and Korea National Research Foundation. Other authors include Hao Chu (PhD ’17), Sungmin Lee, and Jaegun Park of Seoul National University.

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