ACTA

Femtosecond Reflection Spectroscopy in La_1.5Sr_0.5CoO₄

T. Egawa^a, Y. Okimoto^a, R. Fukaya^a,b, K. Onda^c, T. Ishikawa^a, S.-Y. Koshihara^a,b, A. Isayama^d and T. Sasagawa^d
^aDepartment of Materials Science, Tokyo Institute of Technology, Megro-ku, Tokyo 152-8551, Japan
^bCREST, JST, Meguro-ku, Tokyo 152-8551, Japan
^cDepartment of Environ. Chem. and Engineering, Tokyo Institute of Technology, 4259 Nagatsuta, Yokohama, 226-8503 Japan
^dMaterials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Yokohama, 226-8503 Japan

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Ultrafast optical response has been investigated using fs laser system on a perovskite-type cobalt oxide, La_1.5Sr_0.5CoO₄. After the photoirradiation at room temperature, the time profile of relative change of reflectance (Δ R/R) shows a sudden change within the pulse duration ( ≈ 150 fs) and decays with a lifetime of ≈ 330 fs. The sign of Δ R/R after the photoexcitation is positive in the mid-infrared region (at 0.50 eV) while negative in the visible energy region (at 2.0 eV), implying photoinduced change of the electronic structure after the photoexcitation.

DOI: 10.12693/APhysPolA.121.307
PACS numbers: 78.47.J-, 78.47.jg