In article .com,
says...
sorry for not mentioning the dimensions
sheets r 100 micro meter and spot sizes needed are 50 micro meter plz
remember the weld should have atleast 160 micrometer depth(for weld
strength) ...open for any ideas


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...
http://www.lasag.com/index.html
http://www.synrad.com/search_apps/process/welding.htm

Ned Simmons