ATR Crystal Hemisphere Design

Issue

• Why is the crystal shaped the way it is?
• Why does the crystal appear to have a film/coating on the center of it.?

Environment

Nicolet iN10 Microscope

Resolution

The backside of the crystal is hemispherical in shape to create the ATR affect. 

Also a secondary effect of the hemispherical shape is that it creates an immersion effect that helps focus the source energy to a smaller spot size on the contact surface of the crystal. 

The crystal has a reflective coating in the center to only allow source energy to enter at an area of the crystal to direct the energy at the correct incidence angle.