Theodore Maiman invented the world’s first laser which was ruby laser on May 16, 1960.
Ruby Laser is a solid-state laser that uses a synthetic ruby crystal as its gain medium.
It produces deep red light of the wavelength of 694.3 nm.
Reference source:
[1] Wikipedia Contributors. Ruby laser. Wikipedia. Published November 15, 2021. Accessed January 6, 2022. https://en.wikipedia.org/wiki/Ruby_laser.
[2] Potter KS, Simmons JH. Optical gain and lasers. Optical Materials. Published online 2021:369-428. doi:10.1016/b978-0-12-818642-8.00007-7