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Processus électroniques d'excitation et de relaxation
dans les solides diélectriques excités par des impulsions
ir et xuv ultracourtes

Abstract : We studied excitation and relaxation of electrons involved during interaction of visible and
VUV femtosecond pulses with dielectrics. The generated population of hot electrons, having
energy of few eV to few tens of eV above the bottom of the conduction band, is responsible of
phenomena ranging to defect creation to optical breakdown. Owing to two techniques : photoemission
and transient photoconductivity we improve the understanding of the The first
photoemission experiments deal with dielectrics irradiated by 30 fs IR pulses. The photoemission
spectra measured show a large population of electrons which energy rise up to 40 eV. We
interpret this result in terms of a new absorption process : direct multiphotons interbranch
transitions. The 2nd type of photoemission experiments are time resolved "pump/probe" investigation.
We study the relaxation of electrons excited by a VUV pulses. We used the high
order harmonics (HOH) as light sources. We found surprisingly long decay time in the range
of ps timescale. Last type of experiments is photoconductivity studies of diamond samples.
Using HOH as light source we measure the displacement current induced by excited electrons
in the conduction band. Those electrons relax mainly by impact ionisation creating secondary
electrons. Hence by probing the number of electrons we were able to measure the efficiency
of these relaxation processes. We observe a diminution of this efficiency when the energy of
excitating photons is above 20 eV. Owing to Monte-Carlo simulation we interpret this result
in terms of band structure effect.
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Submitted on : Tuesday, February 14, 2006 - 9:46:11 AM
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Jerome Gaudin. Processus électroniques d'excitation et de relaxation
dans les solides diélectriques excités par des impulsions
ir et xuv ultracourtes. Physique Atomique [physics.atom-ph]. Université Sciences et Technologies - Bordeaux I, 2005. Français. ⟨tel-00011599⟩

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