Parameter studies of helium-neon lasers at 543 nm

Previously, there have been little other than empirical reports on the 543 nm helium-neon laser, these have usually revolved around commercial laser tubes. An attempt to describe the behavior of this transition, by measuring the optical gain at 543 nm under different discharge conditions and explaining the results, is made. Initially, empirical results of commercial laser tubes are presented, in an attempt to clarify previously published reports on this transition. A commercial 543 nm laser, oscillating in a single mode, was frequency stabilized to a Zeeman stabilized 633 nm helium-neon laser in a scanning Fabry-Perot interferometer. The long term stability of this laser was estimated as being roughly 1MHz. The output from this laser was used to probe various helium-neon discharges, with the amplification of the beam's intensity being used to measure the variation of optical gain at 543 nm as a function of discharge gas fill and current. This method of measuring the optical gain could resolve changes in the probe beam's intensity of less than 0.001 percent. This experimental technique yielded results for the optical gain at 543 nm, which did not mimic those seen at 633 nm. The optimum total gas pressure of the discharge was found to lie at roughly 2/3 of that seen at 633 nm (measured using the same method), and furthermore the optical gain at 543 nm at the optimum total gas pressure for the 633 nm transition was almost zero. This behavior was explained as being caused by an electron resonance peak at 219 eV observed in the electron excitation cross section to the lower laser state of the 543 nm transition, which is not seen in the 633 nm transition. A numerical model is developed to show the effects of this resonance peak on the optical gain of the laser system as a function of gas pressure, and this predicts a similar result to that observed by the above experiments. Unsuccessful attempts to absorb 19 eV electrons and thus remove the effects of this resonance peak are also described. The behavior of the optical gain at 543 nm as a function of discharge current is found to be explicable using existing helium-neon laser theory.