Abstract: A method and apparatus for producing intense, coherent, monochromatic light from a low temperature plasma are disclosed. The apparatus includes a housing for confining a gas at subatmospheric pressure and including a set of reflectors defining an optical cavity. At least one anode and cathode are positioned within the gas. First control means control the voltage applied to the anode and second control means independently control the temperature of the cathode. The pressure of the gas is controlled by a third control means. An intense monochromatic output is achieved by confining the gas in the housing at a controlled pre-determined reduced pressure, independently controlling the temperature of the electron emitting cathode and applying a predetermined controlled low voltage to the anode. An intermediate mode current is drawn from the cathode and produces in the confined gas, a region having a high density of metastable atomic states leading to a population inversion.