Challenges & Technologies

Sources

LUMI 1.0 will be calibrated using thermal sources and EI-QMS mass spectrometry, which are both established and reliable methods for thermally stable molecules in the mass range up to several kDa.

LUMI 2.0 will foresee the option to be connected to a metal cluster source, a laser-seeded jet source and a post-neutralized ESI source.  

Inertial and Vibrational Phase Averaging

The long baseline increases the instrument's sensitivity to external force fields, in particular also to lab vibrations or Coriolis shifts caused by the rotation of the Earth. Earth's gravity imposes also stricter alignment requirements than in all previous molecule interferometers. These effects will be actively nulled or protocolled and eliminated in post-process correlation.

To address the vibrational sensitivity, we have placed the experiment on anoptical table and suspended a high-mass (160 kg) INVAR interferometer support from a pendulum. Springs, teflon balls, and eddy damping brakes provide additional vibrational isolation and damping. A piezo accelerometer on the interferometer bar as well as an optical Mach-Zehnder interferometer operated in parallel with the molecular interferometer give precise readout of grating motions and can also be used in an active feedback scheme. 

Grating control

Nanometer-precision SMARACT© piezo motors control nearly all degrees of freedom of the three gratings that make LUMI 1.0. They allow excellent alignment, reproducibility and a travel range sufficient to interchange material and optical gratings in situ. 

Detection

LUMI 1.0 is equipped with a quadrupole mass spectrometer (QMS) with a cross beam deflector allows for high-mass resolution with low dark counts and high transmission. The entire detector can be lifted out of the beam-line in favor of other detection methods, such as laser post-ionization TOF-MS or fluorescence imaging.