Embassy of Italy, Cairo
NILES-Cairo University
2009 Italian-Egyptian Year of Science and Technology
Seminar Series
Tracking primary photoinduced events in biomolecules with few-opticalcycle light pulses
Prof. Giulio Cerullo, Department of Physics- Politecnico di Milano
4th January 2009, 10:00 am,
NILES- Cairo University
Abstract
Many light-induced processes in organic molecules, such as energy relaxation, energy/charge transfer and
conformational changes, occur on ultrafast timescales, ranging from 10-14 to 10-12 s. The speed of such
elementary processes is intimately linked to their efficiency, making ultrafast optical spectroscopy an
invaluable tool for their investigation. Pump-probe spectroscopy requires both short pulses, in order to
observe fast dynamics, and broad frequency tunability, to excite a system on resonance and probe optical
transitions occurring at different frequencies. Optical parametric amplifiers (OPAs) are ideal tools for such
experiments, because they provide frequency tunability and support broad gain bandwidths, enabling the
generation of very short pulses. In this talk I will describe a state of the art system, based on two
synchronized OPAs, providing sub-20-fs temporal resolution over a very broad spectral range, from 400 nm
to 1.5 m. After reviewing the pulse generation techniques and the system performance, I will present
selected examples of applications, such as: energy transfer in photosynthetic light harvesting complexes,
electronic and vibrational dynamics in carbon nanotubes, isomerization of rhodopsin.
Giulio Cerullo was born in Milano on February 16, 1965. He received the
degree in Electrical Engineering from the Politecnico di Milano in December
1988, with honours. From 1989 to 1991 he was with the company Baasel
Lasertechnik GmbH (Starnberg, Germany) developing laser systems for
medical applications. From 1991 to 1999 he was staff researcher with the
department of Physics, Politecnico di Milano. In the years 1995-1996 he
visited the Lawrence Berkeley Laboratory (Berkeley, U.S.A) with a Nato
Advanced Research Fellowship. In November 1999 he became Associate
Professor of General Physics with the Department of Physics, Politecnico di
Milano. His research activity has mainly focused on the physics and
applications of ultrashort pulse lasers, covering a wide range of aspects. His
current scientific interests concern generation of few-optical-cycle pulses,
ultrafast spectroscopy with time resolution down to a few femtoseconds,
nonlinear nano-optics and optical waveguide writing by ultrashort pulses. He is the author of about 180
papers in international peer-reviewed journals (H-index : 31, ISI Web of science) and has given over 35
invited presentations at international conferences. He is Topical Editor for the Journal Optics Letters (Optical
Society of America) for the area Ultrafast Optical Phenomena. He is the coordinator of the FP6 European
Project HIBISCUS (Hybrid Integrated BIophotonic Sensors Created by Ultrafast laser Systems).
For information, contact :
Prof. Franco Porcelli, Embassy of Italy in Cairo, tel 27925821 ; email : franco.porcelli@esteri.it
Dr. Tareq Youssef, NILES, Cairo University, tel 012-1000 336, email: tareq.youssef@niles.edu.eg
Embassy of Italy, Cairo
NILES-Cairo University
2009 Italian-Egyptian Year of Science and Technology
Seminar Series
The role of hydrophobicity in -crystallin-hypericin complex:
spectroscopic study
Ass. Prof. Tareq Youssef, National Institute of Laser Enhanced Science- Cairo Univ.
4th January 2008, 11:30 am, NILES- Cairo University
Abstract
Hypericin has been reported as a potent photosensitizing agent exhibiting antiviral, antibacterial,
antineoplastic activities. Although its photophysics and mode of action are strongly modulated by the binding
biomolecules, detailed information about its mechanism of interaction with possible cellular targets, including
proteins, is still lacking. Previous in vitro studies demonstrated that hypericin can be uptaken by intact lens
and is able to bind to the major lens protein "-crystallin". The present study has attempted to determine the
role of protein hydrophobicity upon its interaction with hypericin using the chemical denaturant guanidine
hydrochloride (GdnHCl) and the hydrophobic surface probe, 8-Anilino-1-naphthalenesulfonic acid (ANS).
Fluorescence measurements showed that the increased exposure of tryptophan (Trp) resulting from partial
unfolding of -crystallin incubated with 1.0 mol L-1 of GdnHCl corresponds to the maximum accessibility of
hydrophobic sites to ANS at the same GdnHCl concentration. Interestingly at this additional hydrophobicity of
the protein, hypericin exhibited its maximum fluorescence intensity. This in vitro study indicated that
hydrophobic sites of -crystallin play a significant role in its interaction with hypericin. The binding between
-crystallin and hypericin was found to be enhanced by partial perturbation of the protein. This was implicitly
evidenced by the increased energy transfer efficiency from protein Trp to ANS only at a partially perturbed
protein. A femtosecond study investigating the photoinduced process on a system of hypericin type
chromophore “oxy-blepharismin” complexed with a partially unfolded alpha-crystallin will be presented.
Tareq Youssef was born in Giza(Dokki)-Egypt on Dec.,1st 1964. He received
his Ph.D. degree in Dec. 1997 in Biophysics from the Faculty of Science–
Cairo Univ in collaboration with Istituto di Biofisica-CNR (Pisa-Italy) through
an agreement between The Ministry of Foreign Affairs in Rome and The
Egyptian Academy of Scientific Research and Technology (ASRT). From
1987 to 2004 he was a staff researcher at Basic Science Dept., Res. Inst. of
Ophthalmology affiliated to The Ministry of Higher Education. In 2004, he
became an Associate Professor of Biophysics at National Institute of Laser
Enhanced Science (NILES)- Cairo Univ. During the Period 1998-2005, he
was received around 3 years as postdoctorate fellowship in Istituto di
Biofisica-CNR, kindly granted from International Centre for Theoretical
Physics (ICTP) in Trieste. He is the scientific coordinator of a couple of local
scientific projects and two international projects with Istituto di Biofisica in
Italy and Ecole Normale Supėrieure (ENS) in France. His research activity
was mainly focused on molecular photobiology. In 2007, he visited ENS (Paris-France) through a common
project working on a femtosecond transient (Pump-Probe) spectroscopic technique. His current and future
interest concerns femtobiology and femtochemistry and their applications in biology and medicine. Finally, he
is promoted as a head of Dept. at NILES since Feb. 2005 till now.
For information, contact :
Prof. Franco Porcelli, Embassy of Italy in Cairo, tel 27925821 ; email : franco.porcelli@esteri.it
Ass. Prof. Tareq Youssef, NILES, Cairo University, tel 012-1000 336, email: tareq.youssef@niles.edu.eg
Embassy of Italy, Cairo
NILES-Cairo University
2009 Italian-Egyptian Year of Science and Technology
Seminar Series,
Broadly tunable few-optical-cycle light pulses from optical parametric
amplifiers
Prof. Giulio Cerullo, Department of Physics, Politecnico di Milano
NILES, Cairo University, 6th January 2009, 10:00 am
Abstract
Light pulses with duration of just few optical cycles are important for a number of applications, ranging from
time-resolved optical spectroscopy to high field science. In the last decade such pulses have been generated
by a variety of techniques: directly from a laser oscillator, by spectral broadening in a fused silica fiber or in a
hollow core fiber, and by ultrabroadband optical parametric amplifiers (OPAs). OPAs seeded by a white-light
continuum (WLC) not only provide frequency tunability but also enable to dramatically shorten the pulse
duration because of their broad gain bandwidths. In fact the phase matching bandwidth in an OPA depends
on the group velocity mismatch (GVM) between signal and idler. Broadband gain is achieved when the group
velocities of signal and idler are matched. This condition occurs either for type I phase matching around the
degeneracy point (s =i) or in a non-collinear OPA (NOPA), in which the interaction angles are chosen to
make the signal group velocity equal to the projection of the group velocity of the idler along the signal
direction. In this seminar we will review several configurations of broadband OPAs, enabling the generation
of few-optical-cycle pulses, with duration from 5 to 8 fs, continuously tunable from the visible to the near-IR.
Femtosecond laser micromachining for telecom and optofluidics
applications
Prof. Giulio Cerullo, Department of Physics, Politecnico di Milano
NILES, Cairo University, 6th January 2009, 11:30 am
Abstract
Femtosecond lasers have recently emerged as a powerful microfabrication tool due to their unique
characteristics. The short pulse duration leads to high peak powers and intensities, when focused by a
microscope objective, even at low average powers. In such regime, the interaction of the laser pulse with the
material becomes strongly nonlinear; in particular a very selective absorption (due to the combination of
multiphoton and avalanche ionization processes) occurs only in a small volume around the focus, where the
intensity is the highest, allowing highly spatially selective energy deposition. The deposited energy can in
turn induce a permanent structural modification in a micrometer-sized volume of the material. Femtosecond
lasers can increase the refractive index of glass, enabling single-step, three-dimensional fabrication of
optical waveguides. In addition, femtosecond-laser irradiation of fused silica followed by chemical etching in
HF solution allows the manufacturing of microfluidic channels, due to the enhanced (by up to two orders of
magnitude) etching rate of the irradiated material with respect to the pristine one. This opens the intriguing
possibility of using a single laser system for the fabrication of both microfluidic channels and optical
waveguides and also gives the capability of a real three-dimensional integration of the two structures to
implement novel optofluidic functions.
This talk will present several examples of femtosecond laser fabrication of optical waveguides and
microfluidic channels as well as the integration of laser written optical waveguides in microfluidic chips
fabricated by standard techniques, for applications to telecom and high sensitivity detection of biomolecules.