Detector Gating for Time Resolved Measurements

In this page I report a recent technical development on the Nanospectroscopy SPELEEM microscope: gating by contrast aperture. The principle is the following. A voltage is applied to an electrode inserted in the image plane at the field-limiting aperture in the beam separator of the SPELEEM. The electrode deflects the photoelectron beam in such manner that this is stopped by the contrast aperture. When the voltage is set to zero, the beam passes through the aperture.

The images below are a proof of principle experiment demonstrating magnetic imaging with time resolution using the hybrid mode operation of Elettra. The images display magnetic domains in magnetite islands on Re(0001). The systems is a favorable in the sense that dichroic contrast is large. On the other hand, islands are small and field of view is only 6 microns. Our feeling is that time-resolved measurements can be attempted at field of view of 4, but acquisition times might approach one hour per image. Below you can see a comparison between standard XMCD-PEEM imaging, multi-bunch and single-bunch imaging.

Finally, I show the variation of XPEEM intensity as a function of the pulse delay, for a given pulse with of 30 ns. As can be seen, image intensity goes to zero before and after single bunch, demonstrating that there is no contamination with multi-bunch.

I created this page because I wanted to share with our closest collaborators something that will certainly make it easier to carry out time-resolved PEEM measurements at Elettra. I am indebted to all who contributed making this a reality:

• Matteo Lucian, our technician, who made the electrode in workshop, achieving micromechanics precision using an old piece of machinery.
• Ernst Bauer, Onur Mentes, Stefania Pizzini and Jan Vogel for exchanging ideas and several fruitful discussions.
• Paolo Pittana, Rudi Sergo and Giuseppe Cautero, for invaluable advice on how to make the electrode work and achieving the desired pulse shape with steep edges.
• The Elettra machine group for setting up the hybrid mode so nicely. Alessandro Carniel and Silvano Bassanese, for building the frequency divider that delivers the bunch marker signal and coupling it to our system.