Intermodal tuning behavior of an etalon tuned slm tea-co2 laser

Interference fringes produced by an extra-cavity wedged etalon and recorded with a 128-element pyroelectric detector array have been used to study the mode structure and fine-tuning behavior of a TEA-CO2 laser, which is tuned with a diffraction grating and a temperature controlled intracavity etalon (1). The TEA-CO2 laser can be tuned over a range of about ± 2 GHz centered on each of its strong emission lines, and its longitudinal mode spacing is ∼120 MHz. The wedge and detector array provide an experimental resolution of a few 10's of MHz so that the intermode spacing of the laser can be probed in several well-resolved steps. As the temperature of the intracavity etalon is changed, the fine-scale tuning curve of the laser is a staircase function, with a series of flat (nearly constant frequency) segments separated by sharp jumps to the next longitudinal mode frequency. Oscilloscope traces recorded with a photon drag detector show the laser pulses to alternate, as the frequency scan proceeds, between pure single longitudinal mode structure and a small admixture of a second longitudinal mode. These results will be discussed in the context of the development of a high-power multi-atmosphere continuously-tunable SLM CO2 laser (2).