reddened sunlight can also be scattered by cloud droplets and other relatively large particles, which give the sky above the horizon its red glow.

Lasers

Lasers emitting in the red region of the spectrum have been available since the invention of the ruby laser in 1960. In 1962 the red helium-neon laser was invented, and these two types of lasers were widely used in many scientific applications including holography,

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