The infrared light is extracted from the edge region of dipole D1 of the compact superconducting electron storage ring Helios 2. The nominal source point is located at half the maximum field, i.e., at 2.25 T. The light is collected by a water cooled plane mirror M1 placed at 2.0 m from the source point. Mirror M1 is inclined by 45° with respect to the horizontal and reflects the light vertically to torroidal mirror M2 located 0.4 m above M1 in the same vacuum chamber.

The light is deflected horizontally from M2 to outside the vault forming a beam waist at nearly 4 m away. Then collected by another torroidal mirror M3 placed 8 m downstream from M2 it is deflected vertically down to a plane mirror M4 placed 0.4 m below in the same vacuum chamber. Finally, the light is focused near the wedged diamond window (DW) located at 1.2 m from mirror M4. The DW separates the ultra high vacuum upstream from the fore vacuum downstream. The total geometrical path length from the “hard” edge of dipole D1 to the DW is 12 m. Further downstream, a rotational ellipsoidal mirror M6 is placed at 1.8 m from the DW to deflect and focus the light into the entrance port of the Bruker IFS 66v/s located at 0.8 m from M6. An additional plane mirror M7 is inserted between the FTIR and the ellipsoidal mirror used for deflection, fine tuning of the focus position and alignment of the infrared light entering the interferometer. The end station comprises both, a medium and a high resolution Fourier transform infrared spectrometer (FTIR), the former featuring an infrared microscope.