a stark - tuned laser operating in the 119 micron line of ch 3 oh has an output power of several tens of milliwatts at 30 watts of pump power while exhibiting a doublet splitting of about ten mhz with the application of a stark field on the order of 500 volts / cm . this output power allows for use of the laser in a multi - channel interferometer , while its high operating frequency permits the interferometer to measure rapid electron density changes in a pellet injected or otherwise fueled plasma such as encountered in magnetic fusion devices . the laser includes a long far - infrared pyrex resonator tube disposed within a cylindrical water jacket and incorporating charged electrodes for applying the stark field to a gas confined therein . with the electrodes located within the resonator tube , the resonator tube walls are cooled by a flowing coolant without electrical breakdown in the coolant liquid during application of the stark field . wall cooling allows for substantially increased fir output powers . provision is made for introducing a buffer gas into the resonator tube for increasing laser output power and its operating bandwidth .