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    Thresholds for and Time Dependence of UV-Photon-Induced Desorption of Lithium Atoms from Lithium-Fluoride Single Crystals

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    The rapid pace of development in short-wavelength light sources — ranging from available excimer lasers to projected vuv and xuv free-electron lasers — is stimulating investigations of the electronic photon-materials interactions which may be the rate-limiting processes in catastrophic optical damage.

    We have measured photon-energy thresholds for ground-state neutral Li desorption from single-crystal LiF under ultrahigh vacuum conditions using laser-induced fluorescence, and found that as much as one-fourth of the total yield is traceable to photons with energies less than the LiF band gap. Moreover, time-resolved measurements of the desorption process have enabled us to identify the specific excitonic channels which lead to diffusion-driven, defect-induced desorption in this material. Excitonic energy-transfer mechanisms of this type are characteristic features not only of the alkali halides, but also of alkaline-earth halides, fused silica and many metal oxides.

    Our results demonstrate that mobile surface and near-surface defects can be produced even by low-energy photons, and that the diffusion of these defects drives the formation of metal-rich overlayers in LiF and probably in many other short-wavelength optical dielectrics.


    electronic transitions, LiF, time resolved measurement, ultrahigh vacuum, uv laser damage

    Author Information:

    Haglund, RF
    Vanderbilt University, Nashville, TN

    Tolk, NH
    Vanderbilt University, Nashville, TN

    Committee/Subcommittee: E13.01

    DOI: 10.1520/STP18544S