Making a 50 um collimated beam on a budget

Hello again,

My handy optics engineer has left the country leaving me with a problem that's over my head. I need a low cost (i.e. $500.00) solution to produce a circular, collimated, 405nm beam. My beam needs to be within the target diameter (+/-20%) from 0 - 4" from the output lens and have an output power of about 6.5 mW +/-2mw.

My first thought is to take a 405nm laser with single-mode pigtail coupled into a lens tube with an aspheric lens to collimate it and a couple of plano- convex lenses to reduce the collimation to .002".
This method is more expensive than I like, but it avoids having a pinhole / alignment fixture, which is also expensive.

Any ideas?

Thanks in advance,

Mike