CVD zinc selenide is not poured. It is deposited. A hot mandrel sits in a chamber. Zinc vapor and hydrogen selenide meet on that surface. A polycrystalline crust grows. We take the crust off, make plates, and you core them.
The reactor, not the myth
Commercial IR ZnSe of the size laser OEMs buy is almost always chemical vapor deposition. Melt growth fights selenium vapor pressure and stoichiometry; you can do it in a lab. You do not do it for 800 × 1200 mm class plates. CVD does.
Typical picture: a graphite (or similar) mandrel, a hot-wall or controlled-temperature zone, zinc metal generating vapor, H2Se as the selenium source, hydrogen as the byproduct. Growth is slow by glass-shop standards. Thickness is time plus surface kinetics plus how even the boundary layer stays. KM’s 2020 milestone — high-thickness laser-grade production — is exactly this problem, solved often enough to sell.
Polycrystalline on purpose
The deposit is polycrystalline, often with a columnar grain structure pointing away from the mandrel. Grain size is an optical parameter. Too fine, and you can pay in scatter. Too coarse or too dirty at the boundaries, and 10.6 µm absorption and damage threshold suffer. This is why “CVD ZnSe” is a process name, not a purity grade. Laser grade and optical grade are selections on that process, not different chemistries.
After growth the mandrel is released. You get a curved or plate-like boule depending on tooling. Then: slice, grind both faces (we have the shop photo of slab grinding for surface removal), inspect, and either ship as raw sheet, water-jet as SMTY, or core and edge.
What we do not claim
We do not publish residence times, mandrel alloys, or the exact thermal profile. That is the factory. We do tell you the process is CVD, the plant is Gwangju, and the grade on the line is laser or optical. If a competitor’s glossy PDF implies they melt optical ZnSe in a crucible the size of a car, ask them which century they are describing.
Effective sheet areas we actually photograph in inventory include 800 × 1200 mm and 800 × 1400 mm class plates. That is the point of CVD: area, then you nest blanks.