When an OEM asks for “a ZnSe window for 10.6 µm,” they are really asking three questions at once: how much bulk absorption will heat the optic, how clean is the CVD grade, and whether the AR stack will survive the fluence. Zinc selenide remains the workhorse for mid- and long-wave IR laser delivery because it combines usable transmission from the red edge of the visible through the LWIR with manageable absorption at the CO₂ line — provided the material grade matches the power density.
Grade is not marketing
Laser-grade CVD ZnSe with controlled inclusion size (often specified as a class of inclusion diameter depending on supplier language) matters because scatter centres become damage initiators and thermal hotspots. For high-duty-cycle industrial cutting and medical CO₂ systems, specifying surface quality (40-20 typical, 20-10 on request) and flatness (λ/4 class, tighter when cavity alignment demands it) is as important as the diameter callout.
Coatings decide the system, not the blank
An uncoated ZnSe surface reflects a non-trivial fraction of 10.6 µm energy. Dual-side AR optimised at 10.6 µm is the default industrial path; dual-band stacks (IR plus a visible alignment band) help assembly without forcing a separate HeNe path through a different optic. Always request witness samples when qualifying a new coater or stack revision.
Design traps
Do not assume ZnS is interchangeable at 10.6 µm for high-power CO₂ — dispersion, absorption and hardness profiles differ. Watch thermal lensing: even “good” ZnSe can wavefront-distort under load if cooling and beam diameter are wrong. For RFQ packages, send power, beam diameter (1/e²), CW vs pulsed, environment (humidity, debris), and whether the part is a focusing lens, meniscus or flat window.
Quantum Optx supports ZnSe from blank preparation through coated, inspected optics for OEM repeat production. Use the Spectral Explorer to place 10.6 µm in context with other candidates, then request a quote with drawings.