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DEPHASING OF EXCITONS AND PHASE COHERENT PHOTOREFRACTIVITY IN ZnSe QUANTUM WELLS

TRIPATHY, SUVRANTA K.
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1163704159

Abstract Details

2006, PhD, University of Cincinnati, Arts and Sciences : Physics.
Spectrally resolved and time-integrated degenerate four-wave mixing (FWM) experiments with ultra-short pulses have been used to investigate the relaxation times and coherent interactions of excitons in the Boltzmann and in the quantum kinetic regime in ZnSe single quantum wells (QWs). The interband and interexciton coherences has been investigated in three-pulse FWM experiments using 100 fs pulses in a 10 nm ZnSe QWs. The FWM signals obtained in three-beam FWM experiment are explained by optical Bloch equations (OBEs) for a ten-level model including excitation induced dephasing (EID). Two-beam FWM experiments using 30 fs pulses on a 10 nm ZnSe quantum well reveal marked quantum beats and a pronounced non-exponential decay for delay times smaller ~500 fs. The three-beam FWM trace shows a bi-exponential decay which is attributed to a nonlinear polarization that is caused by the interaction of polarization of third beam with both an exciton grating and an eh-pair grating. Model calculations using the OBEs of a two level system that includes EID at both types of density grating provide information about exciton formation processes involved. We observe coherent exciton-LO-phonon polarons in the FWM spectrum of a 3 nm ZnSe single quantum well using 30 fs pulses. The formation of the new quasi-particles is attributed to a strong phonon coupling that is caused by strong Fröhlich interaction, a huge exciton binding that exceeds the LO-phonon energy and a close resonance between the 2s exciton state and LO-phonon energy. The rapid decay of these coherent quasiparticles is attributed to the disintegration into zero-phonon excitons and free LO-phonons as well as to the inhomogeneous broadening of LO-phonon energies due to disorder and k-space dispersion A novel phase coherent photorefractive (PCP) effect has been observed in ZnSe single QWs using ultra-short pulses that do not overlap in time and its spectral and thermal dependence have been investigated. The observed PCP effect is attributed to the formation of an electron grating formed by the interference of coherent excitons. The experimental results are reproduced by OBEs for a five-level system.
Dr. Hans-Peter Wagner (Advisor)
140 p.
Physics, Condensed Matter
Four-wave mixing; Exciton dephasing; Ultrashort pulses; Quantum kinetics; Coherent polarons; Phase coherent photorefractive effect

Recommended Citations

Citations

  • TRIPATHY, S. K. (2006). DEPHASING OF EXCITONS AND PHASE COHERENT PHOTOREFRACTIVITY IN ZnSe QUANTUM WELLS [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1163704159

    APA Style (7th edition)

  • TRIPATHY, SUVRANTA. DEPHASING OF EXCITONS AND PHASE COHERENT PHOTOREFRACTIVITY IN ZnSe QUANTUM WELLS. 2006. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1163704159.

    MLA Style (8th edition)

  • TRIPATHY, SUVRANTA. "DEPHASING OF EXCITONS AND PHASE COHERENT PHOTOREFRACTIVITY IN ZnSe QUANTUM WELLS." Doctoral dissertation, University of Cincinnati, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1163704159

    Chicago Manual of Style (17th edition)

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This open access ETD is published by University of Cincinnati and OhioLINK.