# What optical resonator configuration produces the most output power for a laser?

For various reasons, I have a HeNe laser setup with two external spherical mirrors that I can position and align at will. I've looked around at various sources, which all make mention of which optical resonator configurations give "decent" or "improved" mode volume and the relative amounts of diffraction losses, but am having trouble nailing down which would ideally give the best output power (I know, it's related to mode volume). I'm pretty confident, based on what I've read, that the spherical cavity configuration would produce lower power outputs, but I can't figure out which of the confocal or the long-radius configurations is better for output power.

So let's keep everything else fixed. Can't change the mirror properties, input power, tube length, etc. Let's also say I don't care about which TEM mode is output nor how hard it is to align the laser. Given this, which optical resonator configuration using two spherical mirrors is better for maximizing output power? Which gives the most bang for your buck? And what are the limitations of this configuration?

For reference, Sam's Laser FAQ - an amazing reference for all things laser - gives a great illustration of many of the common types of configurations ($r$ refers to the radius of curvature of the mirror):

• I don't know if this is possible: can a HeNe laser be used as q-switched? (if yes it could help to get higher power pulses). CO2 lasers are used in in q-switching, they are inhomogeneously broaden gas lasers, so at least the broadening does not seem a fundamental limitation of HeNe. But I cannot find any info about this, so it's probably unpractical for some reason. – scrx2 Sep 4 '17 at 20:09
• @scrx2 I'm just using this as a CW laser. No pulsing – Jim Sep 8 '17 at 12:35