New Source for Ultrafast Laser Pulses

In the stretched-pulse soliton Kerr resonator, a single frequency laser enters a fiber ring cavity, generating a broad bandwidth comb of frequencies at the output that supports ultrashort femtosecond pulses. (Source: M. Osadciw, U. Rochester)

University of Rochester researchers are setting a new standard when it comes to producing ultra­fast laser pulses over a broader range of wavelengths than traditional laser sources. William Renninger, an assistant professor of optics, along with members of his lab, developed a new device, a stretched-pulse soliton Kerr resonator, that enhances the perfor­mance of ultra­fast laser pulses. The work has important implications for a range of engi­neering and bio­medical appli­cations, including spectro­scopy, frequency synthesis, distance ranging, pulse generation, and others.

The device creates an ultrafast laser pulse on the order of femto­seconds, that’s freed from the physical limits endemic to sources of laser light. “Simply put, this is the shortest pulse ever from a gain-free fiber source,” Renninger says. Renninger and his team of graduate research and post­doctoral associates improved upon Kerr resonators, an exciting new alter­native for generating femto­second laser pulses that have been the subject of consi­derable research. The lab overcame a challenge to pulse duration in other versions of Kerr resonators by discovering a new soliton – a short burst or localized envelope of a wave – that maintains its shape while propa­gating at a constant velocity. The solitons generated in Renninger’s device differ from the solitons in other Kerr resonators, speci­fically in the shape and behavior of the stretching pulses they create.

“It is stable in the sense it keeps repeating the same thing over and over, getting longer, then shorter, longer then shorter,” Renninger says. The pulses “feature a broad spectral band­width and a compressed pulse duration of 210 femto­seconds, which is the shortest pulse duration observed to date from fiber Kerr resonators,” the researchers stated.

“There are now commercial products, but they’re very expensive. They are prohi­bitive for many research groups with limited budgets for equipment,” Renninger says. Much of the cost is for expertise, not compo­nents, so his group will use part of their funding to provide consulting for research groups at smaller univer­sities in how to design and build femto­second lasers for basic research. “The ultimate goal is to have a design guide published on our website for everybody,” Renninger says. (Source: Rochester U.)

Reference: X. Dong et al.: Stretched-Pulse Soliton Kerr Resonators, Phys. Rev. Lett. 125, 033902 (2020); DOI: 10.1103/PhysRevLett.125.033902

Link: Institute of Optics, University of Rochester, New York, USA

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