In a new study, the team shows how to eliminate a critical source of noise in\u00a0Brillouin lasers<\/a>, a special class of light source known for its extraordinary purity, producing an ultranarrow spectrum that is almost a perfect single wavelength (or colour) of light.<\/p>\n Light produced from sources like a lightbulb have a broad wavelength spectrum and are fine for everyday use but are too \u2018noisy\u2019 for precision scientific purposes, where lasers are needed.<\/p>\n Brillouin lasers generate light so pure that they can be used in optical atomic clocks, which only lose seconds over many thousands of years. But until now, their potential has been constrained by a phenomenon called Brillouin cascading, in which \u2018parasitic modes\u2019 of light emerge and degrade performance.<\/p>\n \u201cBrillouin lasers are among the most coherent light sources, and you can make them at chip-scale,\u201d said lead author Ryan Russell, a PhD candidate at the\u00a0University of Sydney Nano Institute<\/a>\u00a0and\u00a0School of Physics<\/a>.<\/p>\n \u201cBut once you try to increase their output power, they tend to break up into multiple parasitic modes. These extra modes add noise and steal energy from the fundamental mode, which is the one you want to use. For many real-world applications, that\u2019s quite a problem.\u201d<\/p>\n Speed Bump For a Laser<\/p>\n To solve the problem, the Sydney team turned to \u201cphotonic bandgap engineering\u201d. By burning in nanoscale features \u2013 more than 100 times smaller than a human hair \u2013 directly inside the laser\u2019s optical cavity, the researchers created a precise \u201cdead zone\u201d that blocks the formation of parasitic modes at their origin, while not impeding the primary mode.<\/p>\n These features are called \u2018Bragg gratings\u2019, named after William and Lawrence Bragg, an Australian father and son scientific team who together won the 1915 Nobel Prize in Physics.<\/p>\n \u201cThink of it as carving tiny speed bumps into the light\u2019s racetrack, preventing the noisy by-products from forming,\u201d said co-author\u00a0Dr Moritz Merklein<\/a>, also at Sydney Nano and a researcher in the ARC Centre of Excellence in Optical Microcombs for Breakthrough Science (COMBS<\/a>).<\/p>\n \u201cIn simple terms, we\u2019ve learned how to tame the cascade before it even begins,\u201d Dr Merklein said. \u201cThe photonic bandgap removes the density of states that these parasitic modes rely on to operate. Without available states, the parasitic processes just cannot take place. It\u2019s like trying to shout into the vacuum of space \u2013 the sound has nowhere to go.\u201d<\/p>\n![\"Responsive](\"https:\/\/www.newsbeep.com\/ie\/wp-content\/uploads\/2025\/10\/Website-Banner-Quantum-2.gif\")
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