Knowledge Bank

Millimeter-wave rotational spectroscopy has been applied as a diagnostic probe of the HCN submillimeter-wave gas discharge laser. Although the laser line assignments were $made1$ and unambiguously $confirmed2$ in 1967, the laser mechanism is extremely complex and is not yet well understood. The mid-section of our laser tube is quartz which allows us to propagate our diagnostic probe through the positive column of the laser plasma. The laser oscillation can be Q-switched by chopping the beam with a mechanical shutter. In addition, the discharge itself can be operated in pulsed or cw mode. This allowed us to measure life times of vibrational states and also to observe laser oscillation induced competition effects between different vibrational modes. These data impact questions of current interest including the determination of the excitation mechanism and the basis of the remarkable efficiency of the HCN laser.