Seminar: "Characterization of ultra-short pulsed
laser damage in optical crystals by interferometry and photoelectron
spectroscopy experiments" by Sergey Klimentov
Tuesday, March 11, 2014 11:00 AM to 12:00 PM
CREOL Room 102
CREOL Room 102
Sergey Klimentov
General Physics Institute of
Russian Academy of Sciences
Abstract:
Optical energy deposition and relaxation in wide-band gap
crystals (oxides and halides) was investigated aiming to determine processes in
charge of laser breakdown induced by IR femto- and picosecond laser pulses. In
situ monitoring of electron concentrations around the damage threshold was
performed using ultra-fast interferometry, while their energy was estimated in
photo-electron spectroscopy experiment. In both cases, the same spot on the
surface was exposed to a couple of laser pulses with variable time delay (UV
followed by IR after-exposure) to distinguish stages of conduction band
populating and the following heating of free electrons with possibility of
impact ionization. Breakdown threshold were measured in the same conditions.
This way, the most complete, direct and detailed set of measurements was
performed to characterize electron multiplication and laser damage in these
materials.
In spite of the similar damage dependences and significant
energy of free electrons (> 20-30 eV) observed in all the materials far
below the damage threshold, impact ionization was only observed in those known
to bind the free electrons within self-trapped exitons (SiO2, NaCl).
Oxides of Al and Mg did not reveal multiplication of electrons in spite of
their long lifetime in the conduction band, were their energy seemed to be
directly transferred to heat via electron-phonon coupling. Variation of energy
of the IR heating pulse allowed to show, that achieving of critical electron
density, used as conventional criterion of optical damage, is not valid in the
case of both groups of materials.
For additional information:
Dr. M.J. Soileau
V.P. for Research and Professor of Optics, ECE & Physics
407-823-5538
MJ . Soileau @ ucf . edu
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