I did experiment with green laser..
According to Greg, it must be UD glass then.
On the attached image it is visible that beam is passing through 6 glass elements.
So, washing with windex (diluted..) is safe
BTW.. does anyone know how to dismantle the built-in hood? It is badly damaged and I want to replace it with light plastic tube.
It seems I need to unscrew the cell with UD elements, to remove the hood, but I am not 100% sure this is the case.