Intensity modulation, frequency stabilization, and tuning of a CO laser by an extracavity Stark cell

An investigation was made of the feasibility of modulation and frequency tuning of about 50 lines emitted by a CO laser. Tests were made on various gases and vapors in an extracavity cell and six of them modulated laser radiation: these were NF₃, C₂H₃Cl, NH₃, CF₃I, CH₂O₂, and C₂H₄O₂, which modulated 12, 5, 3, 6, 16, and 4 transitions, respectively. The modulation index was determined for those cases when the polarization of the output radiation of the laser was parallel or perpendicular to the electric field vector. The modulation index could have a positive or negative value. The maximum positive index (4%) was obtained for NH₃ and the P(15) line of the 13–12 stimulated emission transition of the CO laser; the maximum negative index (3%) was obtained using CH₂O₂ and it was exhibited by the P(15) line of the 14–13 transition. In the case of some transitions it was possible to identify a separate component or a group of superimposed components suitable as a reference point in frequency tuning by means of the Stark effect. Four gases were found suitable for stabilized frequency tuning of six stimulated emission transitions in the CO laser. The maximum tuning range (66 MHz) was achieved for the P(17) line of the 11–10 transition using the CH₂O₂ gas for stabilization.