528 is a tough puppy to lase.
It's not that it needs high current, just very clean optics, and a precise gas fill. If I recall, a trace amount of Neon needs to be present for it to lase with any accuracy. Beyond that, it's really hard, and takes a bit of luck.
However, it is
possible as you can see to get it without the Neon, just takes care. My texts mention that with very clean optics, and decent alignment, is it doable.
A snippet from the FAQ where Steve Roberts (Mixed Gas on PL, and LSRFAQ on LPF) speaks on the matter.
(Steve Roberts) said:
I wanted 528 nm from an argon ion laser. I'd only seen it once in a huge Laser Ionics tube at very high pressure. Strangely, that tube had a more or less orange glow at the cathode sheath, much more orange then normal. Now I know why. After a year of research and wondering if my prism was walking out of alignment when cranked to the 528 nm position, I found the solution in a old gas laser text the library was throwing out. It turns out you need a trace of neon in the tube to get the right upper state. No wonder 528 is always labeled "special testing required" from the manufacturer.
PS. Ar also has a 78nm line from the decay process of the electrons to ground state. It's labeled in a few of my tests as a special interest project. However, I would need to find old HR's from used UV AR II/III heads, or from an old 325nm HeCd. Also, I would need sunscreen. If that would even help that deep in the UV. WAY more dangerous that A/B/C as it is much further down the spectrum.
Danger has never stopped me though. Except when I wanted to build an X-Ray machine. Though that's another story.
If a certain someone is reading, how good is krypton at seeing the innards of a circuit board?
/end_inside_joke
