A RF excited diffusively cooled carbon monoxide kilowatts laser is reported.In this laser,the top electrode was cooled with the tap water and the bottom electrode was cooled with the liquid nitrogen to maintain the slab waveguide gas discharge region at a low temperature.In the experiments,a slab waveguide region was excited by a RF transverse gas discharge at a frequency of 90 MHz,a new type of optical resonator consisting of a conventional unstable resonator and a flat feedback mirror was employed.The maximum laser power output of over 1 kilowatts was obtained with a gas composition of P(CO):P(He):P(Xe):P(O2) at a ratio of 24:71:4:1.