The undulators of the ELBE FELs

At the ELBE facility two permanent magnet undulators are installed producing light in the mid and far infrared region.

  • The FEL with the U37 undulator has a tuning range of  ~ 5 - 40 μm (~ 7.5 - 60 THz).
  • The FEL with the U100 undulator has a tuning range of  ~ 20 - 250 μm (~ 1.2 - 15 THz).

Table 1:
The main parameters of the FELBE undulators. The undulators are labelled UλU according to the length λU (in mm) of their magnetic periods.

  
Parameter Undulator
  U37 U100
Undulator period λU 37 mm 100 mm
Number of periods NU 54 38
Undulator parameter Krms 0.4 - 1.35 0.5 - 2.8

The wavelength of the produced light is determined by the energy of the electron beam and by the magnetic undulator field. The latter is characterized by the undulator parameter Krms which is determined by the number NU of undulator periods and by the length λU of a period according to

Krms = eBUrms λ U / (2π mc) ≈ 0.934 BUrms[T] λU[cm], (1)

where BUrms is the rms field amplitude on the undulator axis. (m: electron rest mass, -e: electron charge, c: vacuum velocity of light).