New Approach to Generate Lasers

In this optical microcavity confined light interacts with an atomically thin semiconductor to create particles with negative mass. The device also presents a way to generate laser light with an incrementally small amount of power. (Source: M. Osadciw, U. Rochester)

Most objects react in predictable ways when force is applied to them unless they have nega­tive mass. And then they react exactly opposite from what you would expect. Now Univer­sity of Rochester researchers have succeeded in creating particles with negative mass in an atomically thin semi­conductor, by causing it to interact with confined light in an optical micro­cavity. This alone is “interes­ting and exciting from a physics perspec­tive,” says Nick Vamivakas, an associate professor of quantum optics and quantum physics at Rochester’s Insti­tute of Optics. “But it also turns out the device we’ve created presents a way to generate laser light with an incremen­tally small amount of power.”

The device consists of two mirrors that create an optical micro­cavity, which confines light at different colors of the spectrum depending on how the mirrors are spaced. Researchers in Vamivakas’ lab, including co-lead authors Sajal Dhara and PhD student Chitraleema Chakra­borty, embedded an atomically thin molyb­denum dise­lenide semi­conductor in the micro­cavity. The semi­conductor was placed in such a way that its inter­action with the confined light resulted in excitons from the semi­conductor combining with photons from the confined light to form polari­tons.

“By causing an exciton to give up some of its identity to a photon to create a pola­riton, we end up with an object that has a negative mass associa­ted with it,” Vami­vakas explains. “That’s kind of a mind-bending thing to think about, because if you try to push or pull it, it will go in the opposite direction from what your intuition would tell you.” Other research groups have been experi­menting with similar devices, Vamivakas says, but this is the first device to produce particles with negative mass.

Though appli­cations are “still down the road,” Vamivakas adds, his lab will continue to explore: How the device might serve as a substrate for produ­cing lasers. “With the pola­ritons we’ve created with this device, the prescrip­tion for getting a laser to operate is completely different,” Vami­vakas says. “The system starts lasing at a much lower energy input” than tradi­tional lasers now in use. “We’re dreaming up ways to apply pushes and pulls. Maybe by applying an elec­trical field across the device and then studying how these pola­ritons move around in the device under appli­cation of external force.” (Source: U. Rochester)

Reference: S. Dhara et al.: Anomalous dispersion of microcavity trion-polaritons, Nat. Phys., online 30 October 2017; DOI: 10.1038/nphys4303

Link: Inst. of Optics, Univ. of Rochester, Rochester, USA

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