Lens Savers® protective windows are polished optical crystal windows made from single crystal potassium chloride (KCl) and Sodium Chloride (NaCl). These optical materials absorb very little laser energy at 10.6 microns, which is the wavelength at which CO2 lasers operate. For YAG systems, the windows are made from a type of glass —BK-7— which absorbs little energy at 1064nm, the wavelength at which YAG lasers operate.

Lens Savers® windows are made from materials that have very low refractive indices at their operating wavelengths. KCl, for example, has a refractive index of 1.454 at 10.6 microns and it transmits at better than 93% without application of an AR coating. Reflection losses through the 2 surfaces of an uncoated KCl window at 10.6 microns are 6.8%. NaCl has a refractive index of 1.49 and reflection losses at 10.6 microns are around 8%. Coated BK-7 transmits 99% of the available energy at 1064nm. Uncoated BK-7 has a refractive index of 1.506 at 1064 nm and losses are about 8%. Coated BK-7 transmits over 99% of available energy in a YAG laser at 1064nm.

A Comparison of KCl with ZnSe is instructive to illustrate why the materials used in Lens Savers® work so well. The low refractive index of KCl makes it a much more efficient laser energy transmitter than uncoated ZnSe from which CO2 laser focusing lenses are made. ZnSe has a very high refractive index (2.40)—so high that it is the material of choice in the field of internal reflection spectroscopy where high reflection is desired. Without an anti-reflective (AR) coating, ZnSe will transmit less than 70% of available energy. Reflection losses through the two surfaces of an uncoated ZnSe window are 29% at 10.6 microns. After application of an AR coating to ZnSe, manufacturers claim that transmission at 10.6 microns is 99%. As the delicate AR coating on ZnSe focusing lenses deteriorates from spatter damage and normal cleaning, the performance of the lens degrades.

Unless you are operating near the power limit of a CO2 laser system, you will not need an AR coating on a Lens Savers® window in a CO2 laser system. ICL does not sell AR coated Lens Savers® for CO2 lasers, and we do not recommend AR coatings on Lens Saver® for CO2 lasers because they are too expensive for the nature of the product. However, ICL will provide AR coated windows for CO2 lasers at $23.99 per window in minimum batches of 50 windows for YAG lasers, AR coatings are relatively inexpensive and we offer both uncoated and AR coated windows from stock. We leave it the user to decide whether the extra performance is worth the extra cost of AR coatings..