January 14, 2020
A single semiconductor laser can produce each an amplitude-modulated and a frequency-modulated frequency comb, demonstrating a bodily relationship between two kinds of output beforehand considered impartial.
J. Hillbrand et al., Phys. Rev. Lett. (2020)
A frequency-comb laser concurrently emits many wavelengths of sunshine, with every being equidistant from the subsequent in frequency area. Some emit an amplitude-modulated (AM) beam, which seems as pulsed quite than steady mild, others emit a frequency-modulated (FM) beam, the place the sunshine has a gradual depth however a modulated frequency. As a result of these two kinds of comb produce completely different outputs, researchers thought that their spectra arose from impartial bodily mechanisms. Now, in a brand new experiment, Benedikt Schwarz of the Technical College of Vienna and colleagues show a quantum-dot laser that produces each kinds of frequency combs.
The researchers produce the AM and FM frequency combs utilizing a near-infrared laser, the place the sunshine comes from photons emitted by excited quantum dots. Once they apply a adverse voltage to the dots, they discover that they will excite the dots extra rapidly, and the laser produces an AM beam. With out the adverse voltage, the laser emits a FM beam.
To elucidate the discovering, the crew likens the AM and FM laser outputs to the movement of a gaggle of metronomes. Metronomes are recognized to swing in both synchrony or antisynchrony when positioned on a tabletop, the movement sort relying on the desk’s damping. Within the comb, every frequency to its neighbor to provide a so-called “beat observe” whose frequency is the same as the spacing between the comb’s enamel. If all contributions to the beat observe have the identical part—transfer in synchrony—the beat observe depth is maximized, and the result’s an AM “pulsed” output. Nonetheless, if the laser’s acquire medium is sufficiently damped, the phases antialign, and the beat observe vanishes, resulting in a FM output. Their theoretical work means that many semiconductor lasers can maintain each settings.
This analysis is revealed in Bodily Overview Letters.
Sophia Chen is a contract science author primarily based in Tucson, Arizona.
In-Part and Anti-Part Synchronization in a Laser Frequency Comb
Johannes Hillbrand, Dominik Auth, Marco Piccardo, Nikola Opačak, Erich Gornik, Gottfried Strasser, Federico Capasso, Stefan Breuer, and Benedikt Schwarz
Phys. Rev. Lett. 124, 023901 (2020)
Printed January 14, 2020
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