True or False: A laser is specifically defined by its medium of operation.

A laser is indeed specifically defined by its medium of operation. This is because the medium determines how the laser light is generated and characterized. Lasers operate by stimulating a definite medium, whether it be a gas, solid, liquid, or semiconductor, which then emits light through a process known as stimulated emission.

Each type of laser medium has unique properties that affect the laser's output wavelength, efficiency, and operational characteristics. For example, a carbon dioxide laser uses a gas medium and typically produces infrared light, while a neodymium-doped yttrium aluminum garnet (Nd:YAG) laser uses a solid crystal medium and can emit visible or infrared light. Hence, the classification of a laser is largely reliant on its medium, making this statement true.