Surface prep of acrylic for engraving

I would like to engrave some translucent white acrylic with my 4W diode laser. It shipped with a black dry erase marker. If I don’t coat the plastic with the marker, nothing happens. My question are:

  1. What is the function of the marker?
  2. Is over-the-counter dry-erase the best product for the job?
  3. What about paper covering?
  4. If you use paper, should it be adhered to the plastic, or will the adhesive interfere with the laser?

Part of what makes laser engraving (and cutting) work is that the energy contained in the beam of light is transferred to the work piece. For acrylic materials, especially non-pigmented or slightly pigmented acrylic materials, LED laser frequencies do not excite the plastic. Bored plastic simply sits in place, while excited acrylic jumps up and runs away. CO2 lasers use a frequency that makes all acrylics excited.

The marker is absorbing the energy from your LED beam, getting all hot and bothered and by conduction, transferring that energy to the acrylic. It’s relatively inefficient, but not completely ineffective, as you may have discovered.

Any covering over the acrylic will absorb some of the energy and transfer less to the acrylic.

Thanks for your very informative answer!