Diamond window

There is significant absorption around 4–5 Âµm. Note that this graph does not take into account that the FEL2 window is mounted under Brewster's angle

The refractive index of diamond is very constant in the near-infrared region from 3 Âµm.

Between the optical cavity of FEL1 and the optical transport system there is a diamond window under Brewster's angle. This is quite transparent from 1–230 Âµm, except for a small range around 4–5 Âµm. The window's thickness is specified to be between 0.4–0.6 mm.

There is also a (wedged) diamond beamsplitter in the FELIX optical diagnostic station. This produces two reflections (from front and back plane), which are used to illuminate the pyro and spectrum analyzer.

Physical properties of diamond:

• Refractive index: 2.417 at 589 nm, 2.378 at 3 Âµm
• Brewster's angle: 67.5° at 589 nm, 67.2° at 3 Âµm

References and notes

File:Optical properties of diamond V14 N1 1993 Thomas.pdf

Comparison between diamond and other window materials.

Brewster's angle - the angle under which p-polarized indicent light is almost completely transmitted.

Free-Electron Laser for Infrared eXperiments