Demonstrates a simple way to identify a CO2 lens surface (concave, convex or plano) using the len's surface as a mirror. Identify lens surface: find out whether your CO2 laser lens is : Plano convex lens (Po/Cx) or Meniscus lens (Men)
The way identify the surface is very simple.
Look strait at one of the surface.
If you see your reflection that should be the concave (or plano) side.
If you don't see your reflection - it is the convex side.