Activity 1.7 - Ultrafast phenomena

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15 Νοε 2013 (πριν από 3 χρόνια και 8 μήνες)

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Activity 1.7
-

Ultrafast phenomena

C.
D
e Lisio, S. Solimeno, A. Porzio, A. Bruno, M. Amanti, E. Fasci

Several activities have been run in 2004, all of them employing the Ti:Sa fs laser
source in its two possible configurations, namely high repetition rate

(82 MHz), low
pulse energy (10 nJ) and 1 kHz repetition rate, 1 mJ pulse energy. With the first
configuration, we realized a pump
-
probe experiment for high
-
time
-
resolution
transient reflectivity measurements, aimed to the study of ultrafast relaxation
phe
nomena in metals, semiconductors, manganites and superconductors.
Fundamental processes, such as electron
-
electron and electron
-
phonon collisions and
Cooper pair breaking, occurring in few hundreds of fs to hundreds of ps, can be
followed in their time evo
lution, thus to sheding light on elementary interactions that
determine several characteristics of the condensed matter. This work was performed
in cooperation with Prof. Peluso’s group.

We realized an experiment for producing polarization entangled photon

pairs to be
used as input in quantum logical gates for quantum cryptography devices. The
photon pairs are generated by means of
spontaneous parametric down conversion

(SPDC) in a BBO nonlinear crystal.

Both laser configurations were used for characterizin
g carbonaceous particles
collected from the exhausts of vehicle engines and electrical power stations. With the
time resolved fluorescence polarization anisotropy
(TRFPA) technique and the use
of a streak camera, particle sizes as small as 1.5 nm, with a r
esolution of 0.05 nm can
easily be measured. This research is of great importance for the environmental
science, and, in particular for atmospheric pollution studies.

The high
-
pulse
-
energy laser configuration was employed for laser
ablation/deposition of m
aterials in the fs time regime. The research was developed in
cooperation with Prof. Spinelli’s group, and represents a completion of their studies
with longer laser pulses.

Finally, we studied the time evolution of laser plasmas produced in air. The pump
-
probe technique employed in this experiment allows the determination of the time
profiles of important quantities characterizing the plasma, such as the electron
density and temperature.


Program for 2005

The activities carried out in 2004 will continue in

2005, and will benefit of new
equipments (an optical parametric amplifier (OPA) and a spectrometer with a gated,
intensified CCD camera) that definitely will improve the capability of all the
experimental techniques.

The transient reflectivity experiment
will be used for systematic measurements on
layered heterostructures, on bulk and layered manganites and on superconductors.
We intend to investigate on the effect of the layer thickness on some properties of the
samples, as well as on the dependence of th
e characteristic relaxation times on the
sample temperature. Also scheduled are measurements on innovative materials, such
as metal nanoparticles hosted in a polymeric matrix. The experimental apparatus will
also be improved with the OPA, allowing spectral
ly resolved, non degenerate pump
-
probe experiments. Finally, the use of a photo
-
elastic modulator will open the way to
the study of ultrafast spin interactions, phenomena of fundamental importance in
magnetic materials and superconductors.

A full character
ization of the polarization entangled photon pairs is scheduled for
2005. Coincidence counts from detectors at the exit ports of a polarizing beam
-
splitter, measured in different experimental conditions (laser power, phase
-
matching
angles, etc. etc.) will
allow the definition of the optimal configuration making the
experimental method suitable as a source of entangled photons for quantum
cryptography experiments.

The TRFPA technique will be further improved to achieve a higher time resolution
capable of re
solving internal motion and/or energy transfer of the particles. An effort
will be made to demonstrate the capability of the technique for
in situ

measurements.
To this end, a laminar flame will be used, with the laser sampling the combustion
process at di
fferent height from the burner.