nano size laser weld spot size for stainless steel sheets

Sounds like you should talk to someone in the micro-chip industry. They weld the connecting wire between the silicon chip and the connecting pins. I believe though, that the wire are gold not stainless.

It doesn't sound unreasonable to me, but why don't you try to get one of the laser manufacturers to do an evaluation? I got to spend a few days recently playing with a very large welding laser. One of the things we had to optimize was the amount of defocussing required to weld the very small (~.010 dia) part rather than drill a tiny hole thru it.

Lasag is one possibility, Synrad another...

It's pretty amazing what you can do with e-beam welding, but it's a very expensive process. OTOH, it would almost certainly work for this.

-- Bob (Chief Pilot, White Knuckle Airways)