The red light emitted by a ruby laser is of wavelength ____________. 

Ruby laser

• A ruby laser is a solid-state laser that uses a synthetic ruby crystal as its gain medium.
• Ruby lasers produce pulses of coherent visible light at a wavelength of 694.3 nm, which is a deep red color.
• Typical ruby laser pulse lengths are on the order of a millisecond.
• A ruby laser most often consists of a ruby rod that must be pumped with very high energy, usually from a flashtube, to achieve a population inversion.
• The rod is often placed between two mirrors, forming an optical cavity, which oscillate the light produced by the ruby's fluorescence, causing stimulated emission.
• Ruby is one of the few solid state lasers that produce light in the visible range of the spectrum, lasing at 694.3 nanometers, in a deep red color, with a very narrow line width of 0.53 nm.