SBIR Phase I: Ultraviolet laser for ultra-high-resolution photoemission spectroscopy

This Small Business Innovation Research Phase I project addresses an immediate need for a short-wavelength, narrow-bandwidth, high-brightness light source for ultra-high-resolution angle-resolved photoemission spectroscopy (ARPES). Low-photon-energy laser sources (~6 eV) have recently been applied to ARPES-based studies of superconducting material properties. Although these lasers have demonstrated the advantages of narrow bandwidths, much higher photon energies than those previously obtained will be required for wide acceptance within the industry. Howeve, solid-state nonlinear media cannot be used to generate light with sufficiently high photon energy due to strong absorption. The specific innovation of the proposed research is a high-efficiency gas-phase nonlinear frequency converter that may be harnessed to generate high average powers at photon energies near 11 eV. The high overall efficiency of this coherent source is due to a fortuitous coincidence between an atomic level and a high-power diode pumped infra-red laser. The nonlinear converter maintains the narrow-bandwidth of the drive laser to achieve sub-meV energy resolution at high photon energies. In the Phase I effort, the conversion efficiency of a phase-matched gas-phase nonlinear mixer will be measured in order to verify the technical and commercial feasibility of the light source. The commercial application of this project is primarily to advance the study of modern superconducting materials. As is well-known, room-temperature superconductors with high current-carrying capability will transform every aspect of the energy sector. However, much theoretical and experimental work remains before this elusive goal may be realized. Photoemission spectroscopy is a vital tool for understanding the mechanisms of high temperature superconductivity, but at present, many competing theoretical models of superconductivity cannot be resolved at the current ~5-meV energy resolution limit set by traditional synchrotron light sources. In conjunction with improvements in electron analyzer hardware, the proposed light source will dramatically increase the energy resolution of photoemission spectroscopy to the sub-meV level. The capabilities of the proposed light source will complement those of the workhorse synchrotron, and enable the next generation of superconducting research.