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Two-photon absorption (TPA) measurements are performed on Ge using an open-aperture z-scan setup with 2.05 µm, 0.57 ps pulses from a Ho:YLF regenerative amplifier to resolve discrepancy issues from previous studies using different methods. Uncoated and antireflection-coated Ge samples are compared. The derived TPA coefficient at low intensity is determined to be (40 ± 8) cm/GW while the weak trend of decreasing TPA with intensity is likely due to saturation.
Piotrowski et al. (Wed,) studied this question.