We final[ly] had time to ray trace your configuration. We have determined that using a 2.0x beam expander collimator along with a 2.5″ focusing lens will indeed produce a spot size ~150um with a DOF (depth of focus) of 2.2mm. Please note DOF is defined as 2x the Rayleigh Length. This only works however when the collimator is placed 350mm from the laser. It is also important to note that our 2.5x beam expander will not work at this distance. The full expanded beam diameter exceeds our 15mm clear aperture. Let me know if you have any questions.
Gary, Sales Engineer, Laser Mechanisms