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WFU Physics Seminars

WFU Physics Colloquium

TITLE: Picosecond Transient Absorption Spectroscopy of the Oxide Crystals KNbO3, LiNbO3, KTiOPO4, CdWO4, and PbWO4.

SPEAKER: Henry M. Yochum III,

Department of Physics Wake Forest University

TIME: Friday, July 16, 1999 at 2 PM

PLACE: George P. Williams, Jr. Lecture Hall, (Olin 101)

All interested persons are cordially invited to attend.

ABSTRACT

The fundamental processes of electronic excitation and the subsequent relaxation of electron-hole pairs to lattice defects are becoming well understood in alkali halide crystals; however, these processes are generally not as well known in more complicated materials. In this work, the creation and ensuing relaxation of electron-hole pairs and the lattice defects they produce in oxide crystals is studied on the subpicosecond and picosecond time scale. A tool useful in studying such processes in alkali halides [1,2], ultrafast pump/probe absorption spectroscopy has been applied in this project on KNbO3, LiNbO3, KTiOPO4, CdWO4, and PbWO4.

Radiation induced absorption by 2.9 eV, 0.3 ps, 0.4 mJ/pulse – 0.8 mJ/pulse, laser light was studied as a function of pump/probe delay time on the 0 ps to 250 ps time scale for probe wavelengths in the 500 nm – 940 nm range in the above oxide crystals. Picosecond absorption spectra and their kinetics were measured and compared with ns electron induced absorption data. Defects are suggested to account for the measured absorption spectra and kinetics.

 

[1] Study of F-center formation in KCl on a picosecond time scale, J.N. Bradford, R.T. Williams, and W.L. Faust, Phys. Rev. Letters, 35 (1975) 300.

[2] Femtosecond time-resolved spectroscopy of self-trapping processes of holes and electron-hole pairs in alkali bromide crystals, T. Sugiyama, H. Fujiwara, T. Suzuki, and K. Tanimura, Phys. Rev. B, 54 (1996) 109.
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