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Need help focusing a 405nm or 10.6 uM laser to 1-25 micron spot

  1. Apr 18, 2012 #1
    Hi all, I'm a total NEWB to this forum, so Hi!

    I need help deciding which laser to go with, and choosing optics (I'm almost a complete optics NEWB, I don't know any of the simple equations by heart)

    I'm working on microfluidics, and am building a custom CNC laser etcher that has a step size of about 0.2 microns. I need to cut about 50 microns depth of a silicone, PDMS, and another 50 microns depth of acrylic.

    I'm not sure whether its more realistic and/or cheaper to go with a CO2 laser of the 405nm laser. I know CO2 cuts my material, but electronics are higher voltage, its physically larger, and optics are more expensive and working distance won't be as large. Blue lasers have a worse beam profile, are untested with my material (though likely to work), have lower power, but optics are much cheaper and its easier to get a small spot size.

    I know in either case I'll need a beam expander (galilean) and a focus lens (plano convex I think).

    Some rough calculations:
    Spot Diameter = ( 4 * wavelength * (lens focal length) ) / ( pi * beam
    diameter )

    If that's true, then for a 2mm focal length and a 1W 405nm wickedlaser's 5mm beam:
    (4 * 0.405 * 20000)/(3.14 * 5000) = 2.06 microns

    For CO2 (10.6 micron wavelength) @ 20mm focus with 2mm beam (no expansion):
    (4 * 10.6 * 20000)/(3.14 * 2000) = 135 microns
  2. jcsd
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