Optical absorption in ion-bombarded magnetic garnet films

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Abstract
Optical absorption measurements are reported for the damaged surface layers produced by proton and neon bombardment of iron-garnet liquid-phase-epitaxial films. The excess optical absorption is shown to be an absorption tail on O(2p)→Fe(3d) charge-transfer bands centered near 4 eV with about 10% contributed by higher-energy optical transitions. The distribution of states for Ne bombardment is different from that for H bombardment, and in the case of Ne the state distribution depends on the dose. Saturation at a photon energy of 2.2 eV occurs at an absorption coefficient of ∼2×104 cm−1. The average damage density over the damaged layer thickness is observed to increase with decreasing H energy, in agreement with hard-bubble-suppression data and nuclear stopping power considerations. Based on optical absorption and hard-bubble-suppression results it is estimated that the dose window for hard bubble suppression corresponds roughly to an average disorder range from ∼3–30% amorphous (amorphous defined optically). Annealing studies show that no simple activation energy description applies to the damaged material. Deep states anneal out more rapidly than shallow states for both H and Ne bombardment.