LODCM

A Large Offset Double Crystal Monochromator (LODCM) is available at XPP. It creates a new beampath 600 mm north of the original beam path. All beamline components can be translated 600 mm to this new operation position. The LODCM can either operate with Si(111) or thin C* crystals. When operating with the latter, it does not only provide a better energy resolution (DE/E = 5.3x10^-5), but most importantly allows to multiplex with another instrument located downstream in the Far Experimental Hall (FEH).

When operating with the former, only XPP uses the LCLS beam; it nevertheless allows to rapidly provide the beam to any of the FEH instruments by translating the first Silicon LODCM crystal from the beam path.

The first thin C* crystal reflects ~0.5 eV bandwidth with almost 100% reflectivity into the mono branch while the other photon energies propagate through the diamond to the FEH with a 50-70% transmission depending on the photon energy.

The Si(111) option would not allow multiplexing, has a bandwidth of 1 eV and gives twice as many photons to the mono branch as compared to C*.

For more details, check the article in Review of Scientific Instrument. For basic alignment procedures of the LODCM go here