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For optical lasers, these irregular spurts – or filamentation – result from the index of refraction changing in the laser material.—Thomas Linker, The Conversation, 15 Oct. 2025 Light travels through water at three-quarters its speed in a vacuum, making water’s index of refraction 1.33.—Bysara Reardon, science.org, 5 Sep. 2024 The higher the index of refraction, the slower light travels in that medium.—Rhett Allain, WIRED, 23 Aug. 2024 Similarly, a time mirror is formed by an abrupt change in the index of refraction—but in time.—IEEE Spectrum, 30 Aug. 2023
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