A Free Electron Laser Photoemission Electron Microscope System (FEL-PEEM)

We report rst results from our e ort to couple a high resolution photoemission electron microscope (PEEM) to the OK-4 ultraviolet free electron laser at Duke University (OK-4 /Duke UV FEL). The OK-4 /Duke UV FEL is a high intensity source of tunable monochromatic photons in the 3{10 eV energy range. This tunability is unique and allows us to operate near the photoemission threshold of any samples and thus maximize sample contrast while keeping chromatic aberrations in the PEEM minimal. We have recorded rst images from a variety of samples using spontaneous radiation from the OK-4 /Duke UV FEL in the photon energy range of 4.0{6.5 eV. Due to di erent photothreshold emission from di erent sample areas, emission from these areas could be turned on (or o ) selectively. We have also observed relative intensity reversal with changes in photon energy which are interpreted as density-of-state contrast. Usable image quality has been achieved, even though the output power of the FEL in spontaneous emission mode was several orders of magnitude lower than the anticipated full laser power. The PEEM has achieved a spatial resolution of 12 nm.

Duke Scholars

Author Ying Wu Physics