Two grades. Same formula. Same CVD. Different rejection criteria. If you only tell us “ZnSe window, Ø25.4 × 3 mm,” we will ask which life it is going into.
Laser grade
This is the CO2 material. The number that matters is bulk absorption at 10.6 µm, plus damage-related scatter. High-power focusing lenses and output couplers live or die on parts-per-million-class absorption. Heat that does not leave through 18 W/m·K conductivity becomes focus shift, then coating failure, then a crater. We quote laser grade when the print says CO2, resonator, kW, or 10.6 µm AR.
Optical grade
This is the imaging and spectroscopy material. Thermal cameras, FTIR windows, dual-band sight glasses, medical IR paths that are not surgical resonators. You care about homogeneity, scatter, cosmetic quality, and broadband transmission. Absorption at 10.6 µm can be allowed higher because nobody is putting a kilowatt through it. It is usually the better economic choice for those jobs. It is the wrong choice for a cutting-head lens.
How to write the line
| If the optic… | Specify |
|---|---|
| Focuses or outcouples a CO2 beam | Laser grade + AR (10.6 or dual-band) |
| Looks at 8–12 µm scene radiance | Optical grade + LWIR AR |
| Is a raw blank you will grind and coat | Grade + SMTY / core / edged |
| Must pass a HeNe and a CO2 | Laser grade, dual-band AR, say so |
We stock and cut both. Mixing them on a BOM because the density is the same is how a thermal-camera window ends up in a laser cabin. Density will not save you. Absorption will find you.