Spektor, Marat

Short-pulse laser interaction with metals is a subject of practical engi-
neering as well as fundamental scientic research.
From the point of view of fundamental science, short-pulse laser irradi-
ation has the ability to bring material into a highly non-equillibrium state
and provides unique insights into material behavior under extreme condi-
tions that cannot be easily attained by any other means. Indeed, scattering
between electrons and phonons or impurities/defects on the femtosecond
time scale was already implicitly conceived in the rst microscopic theories
of electrical resistance [1], and has been studied extensively under Three
Temperature state conditions (e.g. in transport measurements) [2].
However, only the rapid advances of time-resolved spectroscopy during
the past decades have made it possible to distinguish directly the dier-
ent elementary scattering mechanisms of photo-excited carriers. In these
experiments, an ultrashort light pulse excites the electrons. This collec-
tive electron excitation rapidly dephases, giving an excited, non-thermal
distribution of interacting electrons. Consequently this non-equilibrium
distribution will (i) redistribute its energy by scattering among the quasi
particles themselves via electron-electron (e 􀀀 e) scattering, leading to in-
ternal thermalization of the electronic system and (ii) transfer energy to
the lattice via electron-phonon (e 􀀀 ph) scattering, leading to cooling and
relaxation within the lattice.
The eects described so far have a local spatial impact on the dynam-
ics of photo-excited carriers. The non-local nature of the spatio-temporal
dynamics of electron and lattice temperatures is attributed to the diusion
of heat in metals, which is crucial for a variety of applications of metal
nanostructures.
The main goal of the thesis is to research and analyze various processes
related to the ultrafast dynamics of charge carriers in laser heated metals.
In particular, analysis will be performed regarding the thermalization
of charge carriers which can be attributed to the e 􀀀 e scattering eect,
the relaxation of carriers which can be attributed to the e 􀀀 ph scattering
eect and the non-local thermo-optical response that is due to the eect
of thermal conductivity and leads to heat diusion. Comparison between
dierent time scales related to each one of the processes will be presented.
Further, a thorough analysis of the optical properties of Au will be
presented. According to our model, two additional eects modify the di-
electric function of Au: (i) the band shifting eect, which is related to the
temperature dependence of the chemical potential of Au and (ii) the dipole
matrix element temperature dependence (DMETD), which is related to the
temperature dependence of the dipole matrix element. As far as we know,
none of these eects and their physical interpretation has been presented
in the current literature.
The spatio-temporal dynamics of optically-induced transient Bragg grat-
ings will be presented and analyzed for dierent excitation conditions.
Finally, potential application of these phenomena in the eld of ultrafast
optical switching will be discussed.