If you design a REALLY good reflector you might be able to get away with one linear lamp, but It really will be easier with two. And if you only use one, it HAS to to have an active area of at least the length of the rod. If it's only half the length it wont lase.
The higher the pulse width and duty cycle, the more cooling it will need. Some just allow cold tap water to run through tubing to cool the resonant cavity and especially the rod and then it flows down the drain. The rod will crack if it overtemps. At least that was how Yags reacted to excessive heat.
Omg, I'm still waiting for my occasion to buy such thing, it's amazing, also as I remember ruby rods provide 670nm, also the power you can get from it ;s
I have installed some Solar Tubes in my house, and the inside of those are highly reflective. They are also curved already, so it wouldn't be hard to bend it into a smaller diameter tube. I believe you can buy just tube extensions fairly cheaply
The rod needs to be coated on each face - one 100% reflective and the opposite 50%. The 50% face will emit the beam.
It looks like the rod is lightly doped so your "pumping power" will be reasonable. You will need to acquire large, high-voltage capacitors - I',m talking about perhaps 5 to 10 100 micro farads at 5 KV. These puppies are big - oil filled and weigh about 50 # each. To that you add a HV DC powersupply to charge the caps up - a trigger circuit (20-25kv spark) and presto - a giant pulse.
I used just this design to open the Chicago 1963 Science fair - bursting a balloon 20 feet away with ribbons tied to it.