Experimental Studies on Longitudinal Mode Characteristics of a Hollow Cathode He-Cd+ White Light Laser

A hollow cathode CW He-Cd+ white light laser can oscillate simultaneously at three primary colors (five transitions) in a single tube. The frequency characteristics are important parameters in many applications. Therefore, we have investigated the longitudinal mode of our white light laser. In our experiment, we have found that the red and green transitions oscillate in a single longitudinal mode in spite of a wide gain profile and that the blue transition oscillates in a few longitudinal modes. We consider that this single-mode operation can be caused by hole burning due to mode competition between the longitudinal modes and the saturation coupling. Furthermore, we measured the pressure broadenings and the natural linewidths of the five transitions upon changing of the He gas pressure in the He-Cd+ white light laser.