Radiation is transported in a free space optical mode, using a periodic focussing system, after initial collimation.
Shorter wavelengths require only the initial collimation.
The clear aperture of the system is 10 cm. The cavity dump couplers use a pair of specially shaped mirrors that convert the highly asymmetrical waveguide mode to an approximately round mode for transport. Z-cut crystal quartz windows isolate the high vacuum of the FELs. Each output port has a 2 mm thick TPX window. A built in diagnostic station permits monitoring of power level and frequency.