Erm.. Everything about everything?
I'd say advanced. I've held my own in a university lab, as long as they keep the equations out of the topic. Gas is the one realm that I can really talk for days, though I am by far nowhere near "expert".
Hell ... I almost feel boastful claiming "advanced".
Though there's the added benefit of starting with gas I'd say. On a fundamental level, all lasers are the same. There's a pump source, whether electrical, light, heat, etc. There's a gain medium excited by this source. Again, whether that's gas, a crystalline lattice doped with some rare earth metal, or a semiconductor. Then there are mirrors to create the cavity, gathering the output light, allowing it to resonate and "gain", and releasing a percentage of this light in a coherent beam.
On a basic level, they're all the same. Pump, gain medium, mirrors. The great thing about gas is that you can, with ease, manipulate the cavity to do whatever you want. I say "with ease" as in it is very easy to change something. Not that it's easy to change from one working system, to another, it's just easy to make changes. Making the right changes is the challenge.
So I guess, yes, I'd say advanced. Though again, I do not want to sound boastful or anything. I still have TONS to learn. If anything, the past week and unaligned 532nm cavity in front of me can attest to that. As can anyone I have skyped with over the same period.
On the bright side, I can now identify 1064nm over 808nm ... Soo ... there's that.