New light source to revolutionise photoelectron spectroscopy
The laser-based ARPES technique is a recently introduced promising technology used to study photoemission of electrons from a sample. Using monochromatic ultraviolet light to excite photoelectrons from crystalline solids, it measures intensity distribution as a function of their kinetic energy and emission angle. Since the kinetic energy of ejected electrons is highly associated with the internal electronic structure, analysis of the photoelectron spectroscopy provides further insight into the fundamental physical and chemical properties of the material. Within the LASER-ARPES (Laser based photoemission: Revolutionizing the spectroscopy of correlated electrons) project, scientists unveiled an alternative laser-based ultraviolet light source that largely overcomes limitations associated with synchrotron light sources. The high costs to construct and maintain the accelerator and the need to convert a broad range of wavelengths into one containing a narrow band, which is an inefficient process, pose a barrier to widespread use of synchrotron radiation. The project team developed a laboratory-based ARPES system that uses a compact amplified diode laser with two resonant frequency doublers as excitation sources. Compared to the currently used synchrotron ARPES beamlines, this laser provides two orders of magnitude higher luminous flux in a much narrower bandwidth. First test experiments with this new source were performed on the sp-surface states in Cu(111), a famous model system for studying electronic structure of materials. Scientists were able to resolve for the first time a minute lifting of the spin degeneracy in this state, which arises from the broken inversion symmetry at the surface. LASER-ARPES' new light source revolutionises photoelectron spectroscopy, providing unprecedented insight into the electronic structures of materials. It can also markedly enhance the bulk sensitivity of ARPES, enabling investigation of materials that were not previously possible.
Keywords
Photoelectron spectroscopy, angle-resolved photoemission spectroscopy, ultraviolet, LASER-ARPES
