KASHA RULE
Polyatomic molecular entities luminesce with appreciable yield only from the lowest excited state of a given multiplicity. There are exceptions to this rule.

KASHA-VAVILOV RULE
The quantum yield of luminescence is independent of the wavelength of exciting radiation. There are exceptions to this rule.

KOOPMANS' THEOREM
See photoelectron spectroscopy.

KRYPTON ION LASER
A CW or pulsed laser emitting lines from 337 to 859 nm from singly ionized krypton. Principal emissions are at 530.9, 568.2, 647.1, and 752.5 nm.

See gas lasers.