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Title: Ultrafast XAFS Measurements on Laser Excited Ge Films

Abstract

Laser-pump/x-ray-probe measurements were made on Ge films with nominal time-delay steps of 18 ps. The response of the Ge lattice to the excitation of a high efficiency 200 fs pulse laser operating at 800 nm wavelength and at the Advanced Photon Source (APS) ring frequency of 272 kHz is probed by x-ray absorption fine structure (XAFS) measurements which determine the time dependences of the local structure. Initially the lattice response is dominated by a large increase of the RMS nearest neighbor bond disorder that decays within a single delay step. The next nearest neighbor RMS disorder shows an increase delayed by {approx} 30 ps, consistent with only optical modes dominating the initial lattice response and other phonons being excited more slowly. The different rate of excitation of optical than the rest of phonons require a different mechanism for exciting the optical phonons. Because the laser excites electrons from binding to anti-binding states, a Franck-Condon like effect is suggested as the cause of this initial response, instead of the standard hot electron-hole coupling to phonons.

Authors:
;  [1];  [2]
  1. (UWASH)
  2. (
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Org.:
USDOE
OSTI Identifier:
1009010
Resource Type:
Conference
Resource Relation:
Conference: 13th International Conference on X-ray Absorption Fine Structure-XAFS13;9-14 July 2006;Stanford, California, USA
Country of Publication:
United States
Language:
ENGLISH
Subject:
43 PARTICLE ACCELERATORS; ABSORPTION; ADVANCED PHOTON SOURCE; EFFICIENCY; ELECTRON-HOLE COUPLING; ELECTRONS; EXCITATION; FINE STRUCTURE; LASERS; OPTICAL MODES; PHONONS; TIME DELAY; TIME DEPENDENCE; WAVELENGTHS

Citation Formats

Stern, E.A., Brewe, D., and APS). Ultrafast XAFS Measurements on Laser Excited Ge Films. United States: N. p., 2007. Web.
Stern, E.A., Brewe, D., & APS). Ultrafast XAFS Measurements on Laser Excited Ge Films. United States.
Stern, E.A., Brewe, D., and APS). Thu . "Ultrafast XAFS Measurements on Laser Excited Ge Films". United States. doi:.
@article{osti_1009010,
title = {Ultrafast XAFS Measurements on Laser Excited Ge Films},
author = {Stern, E.A. and Brewe, D. and APS)},
abstractNote = {Laser-pump/x-ray-probe measurements were made on Ge films with nominal time-delay steps of 18 ps. The response of the Ge lattice to the excitation of a high efficiency 200 fs pulse laser operating at 800 nm wavelength and at the Advanced Photon Source (APS) ring frequency of 272 kHz is probed by x-ray absorption fine structure (XAFS) measurements which determine the time dependences of the local structure. Initially the lattice response is dominated by a large increase of the RMS nearest neighbor bond disorder that decays within a single delay step. The next nearest neighbor RMS disorder shows an increase delayed by {approx} 30 ps, consistent with only optical modes dominating the initial lattice response and other phonons being excited more slowly. The different rate of excitation of optical than the rest of phonons require a different mechanism for exciting the optical phonons. Because the laser excites electrons from binding to anti-binding states, a Franck-Condon like effect is suggested as the cause of this initial response, instead of the standard hot electron-hole coupling to phonons.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Jan 18 00:00:00 EST 2007},
month = {Thu Jan 18 00:00:00 EST 2007}
}

Conference:
Other availability
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