Short answers, pulled from the story.
Theodore H. Maiman operated the first functioning laser on the 16th of May 1960 at Hughes Research Laboratories in Malibu, California. It used a flashlamp-pumped synthetic ruby crystal to produce red light at 694 nanometers and could only fire in pulses.
Laser is an acronym for light amplification by stimulated emission of radiation. Because a laser produces light by itself, it is technically an optical oscillator, leading one observer to joke that LOSER, for light oscillation by stimulated emission of radiation, would have been more accurate.
Laser light is coherent, which ordinary light is not. Spatial coherence lets a laser focus to a tiny spot and stay narrow over great distances, while temporal coherence gives it a very narrow frequency spectrum, properties a lightbulb or star cannot match.
Stimulated emission is the process where a passing photon triggers an atom to release a second photon identical in wavelength, phase, and polarization. Both photons can then trigger further emissions, creating a chain reaction when enough atoms sit in an excited state, a condition called population inversion.
Credit for the laser remains unresolved among historians. Gordon Gould recorded the term and an open-resonator design in his 1957 notebook and filed a patent in April 1959, but the patent office awarded the patent to Bell Labs in 1960, provoking a twenty-eight-year legal fight; Gould won a significant infringement claim only in 1987.
Lasers are used in barcode scanners, compact disc players, laser printers, fiber-optic communication, industrial cutting and welding, and medicine, including cancer treatment and eye surgery. The first widely noticeable use was the supermarket barcode scanner in 1974, and global industrial laser sales in 2023 reached 21.85 billion dollars.
Yes, even low-power lasers of only a few milliwatts can harm eyesight, because the eye focuses the coherent, low-divergence beam into an extremely small spot on the retina and causes localized burning in seconds. Lasers carry safety class numbers from Class 1, which is inherently safe, to Class 4 at 500 milliwatts or more, which can burn skin.