A ruby laser is a solid state laser. It used a synthetic ruby crystal as its gain medium.
It was the first type of laser invented, & was first operated by Theodore H Maiman at Hughes Research Laboratories in 1960.
The ruby laser produces pulses of visilight at a wavelength of 694.3 nm which appears as deep red to human eyes.
Typical ruby laser pulse lengths are on the order of a millisecond. These short pulses of red light are visible to the human eyes, if the viewer carefully watches the target area where the pulses will fire.
Ruby laser have declined in use with the discovery of better lasing media. They are still used in a number of application where short pulses of red light are required.
Holographers around the world produce holographic portraits with ruby lasers, in sizes up to a metre squared.
The red 694 nm laser light is preferred to the 532 nm green light of frequency doubled.
Many non-destructive testing labs use ruby laser to create holograms of large objects such as aircraft tyres to look for weakness in the lining.