ABSTRACT
The continuous-wave He–Cd laser is perhaps the best known and most widely used metal vapour laser. It produces visible laser output in the blue at 441.6 nm [1] and ultraviolet output at 354.0 and 325.0 nm [2]. The blue transition produces the most power output [3], while the 354 nm transition is the weakest. A number of other lasers in the green and red portions of the spectrum have been observed in various types of He–Cd discharges. However, these lasers are not available in the commercial He–Cd laser that operates in a positive column type of dc discharge, similar to that of the He–Ne laser. Hence, these other visible transitions will not be dealt with further in this discussion.
