All,
A while back I purchased a surplus lot that had ZnSe beam combiner optics. They are brand new unused and still in protective packaging. They are 15mm diameter by 1.5mm thick. They are designed to be placed in the CO2 beam at a 45 degree angle. The CO2 passes through with very little loss. (< 5%) because it is anti-reflective coated for 10.6um. A red laser is placed to strike the optic as if it is a mirror at 45 degrees. It is coated to reflect the red (630-680nm) so it is combined directly on top of the CO2 (10.6um) beam. When properly aligned, you get your red dot exactly where the CO2 beam strikes at all times, which is vastly superior to a beam coming in from the side that only hits at the focus point. These sell for $99 + $15 shipping on Ebay.
http://www.ebay.com/itm/Beam-Combiner-Optic-for-CO2-Laser-Red-aiming-diode-/390306503416?pt=LH_DefaultDomain_0&hash=item5ae0149af8I put one on my laser, and I sold one to a friend. I have 6 remaining.
I am selling mine to the first 6 USA customers who can pay me by paypal for $70 each. No charge for shipping because I will drop them in an envelope and use regular US post office.
Private message me for purchase. - John