812 research outputs found
Characterization of femtosecond laser written waveguides for integrated biochemical sensing
Fluorescence detection is known to be one of the most sensitive among the different optical sensing techniques. This work focuses on excitation and detection of fluorescence emitted by DNA strands labeled with fluorescent dye molecules that can be excited at a specific wavelength. Excitation occurs via optical channel waveguides written with femtosecond laser pulses applied coplanar with a microfluidic channel on a glass chip. The waveguides are optically characterized in order to facilitate the design of sensing structures which can be applied for monitoring the spatial separation of biochemical\ud
species as a result of capillary electrophoresis
Laser-driven quantum magnonics and THz dynamics of the order parameter in antiferromagnets
The impulsive generation of two-magnon modes in antiferromagnets by
femtosecond optical pulses, so-called femto-nanomagnons, leads to coherent
longitudinal oscillations of the antiferromagnetic order parameter that cannot
be described by a thermodynamic Landau-Lifshitz approach. We argue that this
dynamics is triggered as a result of a laser-induced modification of the
exchange interaction. In order to describe the oscillations we have formulated
a quantum mechanical description in terms of magnon pair operators and coherent
states. Such an approach allowed us to} derive an effective macroscopic
equation of motion for the temporal evolution of the antiferromagnetic order
parameter. An implication of the latter is that the photo-induced spin dynamics
represents a macroscopic entanglement of pairs of magnons with femtosecond
period and nanometer wavelength. By performing magneto-optical pump-probe
experiments with 10 femtosecond resolution in the cubic KNiF and the
uniaxial KNiF collinear Heisenberg antiferromagnets, we observed
coherent oscillations at the frequency of 22 THz and 16 THz, respectively. The
detected frequencies as a function of the temperature ideally fit the
two-magnon excitation up to the N\'eel point. The experimental signals are
described as dynamics of magnetic linear dichroism due to longitudinal
oscillations of the antiferromagnetic vector.Comment: 25 pages, 10 figure
Effects of tunable excitation in carotenoids explained by the vibrational energy relaxation approach
V. B. acknowledges funding by the Leverhulme Trust Research Project Grant RPG-2015-337. J. H. and C. N. L. acknowledge funding by the Austrian Science Fund (FWF): START project Y 631-N27. D. A. acknowledges support by the Research Council of Lithuania (No MIP-090/2015). G. C. acknowledges support by the European Research Council Advanced Grant STRATUS (ERC-2011-AdG No. 291198). G. C. and J. H. acknowledge funding by Laserlab-Europe (EU-H2020 654148)
Nonequilibrium dynamics of photoexcited electrons in graphene: Collinear scattering, Auger processes, and the impact of screening
We present a combined analytical and numerical study of the early stages
(sub-100fs) of the non-equilibrium dynamics of photo-excited electrons in
graphene. We employ the semiclassical Boltzmann equation with a collision
integral that includes contributions from electron-electron (e-e) and
electron-optical phonon interactions. Taking advantage of circular symmetry and
employing the massless Dirac Fermion (MDF) Hamiltonian, we are able to perform
an essentially analytical study of the e-e contribution to the collision
integral. This allows us to take particular care of subtle collinear scattering
processes - processes in which incoming and outgoing momenta of the scattering
particles lie on the same line - including carrier multiplication (CM) and
Auger recombination (AR). These processes have a vanishing phase space for two
dimensional MDF bare bands. However, we argue that electron-lifetime effects,
seen in experiments based on angle-resolved photoemission spectroscopy, provide
a natural pathway to regularize this pathology, yielding a finite contribution
due to CM and AR to the Coulomb collision integral. Finally, we discuss in
detail the role of physics beyond the Fermi golden rule by including screening
in the matrix element of the Coulomb interaction at the level of the Random
Phase Approximation (RPA), focusing in particular on the consequences of
various approximations including static RPA screening, which maximizes the
impact of CM and AR processes, and dynamical RPA screening, which completely
suppresses them
Quantum interference between charge excitation paths in a solid state Mott insulator
The competition between electron localization and de-localization in Mott
insulators underpins the physics of strongly-correlated electron systems.
Photo-excitation, which re-distributes charge between sites, can control this
many-body process on the ultrafast timescale. To date, time-resolved studies
have been performed in solids in which other degrees of freedom, such as
lattice, spin, or orbital excitations come into play. However, the underlying
quantum dynamics of bare electronic excitations has remained out of reach.
Quantum many-body dynamics have only been detected in the controlled
environment of optical lattices where the dynamics are slower and lattice
excitations are absent. By using nearly-single-cycle near-IR pulses, we have
measured coherent electronic excitations in the organic salt ET-F2TCNQ, a
prototypical one-dimensional Mott Insulator. After photo-excitation, a new
resonance appears on the low-energy side of the Mott gap, which oscillates at
25 THz. Time-dependent simulations of the Mott-Hubbard Hamiltonian reproduce
the oscillations, showing that electronic delocalization occurs through quantum
interference between bound and ionized holon-doublon pairs.Comment: 4 figures and supplementary informatio
Scaling-Up Techniques for the Nanofabrication of Cell Culture Substrates via Two-Photo Polymerization for Industrial-Scale Expansion of Stem Cells
Stem-cell-based therapies require a high number (106–109) of cells, therefore in vitro expansion is needed because of the initially low amount of stem cells obtainable from human tissues. Standard protocols for stem cell expansion are currently based on chemically-defined culture media and animal-derived feeder-cell layers, which expose cells to additives and to xenogeneic compounds, resulting in potential issues when used in clinics. The two-photon laser polymerization technique enables three-dimensional micro-structures to be fabricated, which we named synthetic nichoids. Here we review our activity on the technological improvements in manufacturing biomimetic synthetic nichoids and, in particular on the optimization of the laser-material interaction to increase the patterned area and the percentage of cell culture surface covered by such synthetic nichoids, from a low initial value of 10% up to 88% with an optimized micromachining time. These results establish two-photon laser polymerization as a promising tool to fabricate substrates for stem cell expansion, without any chemical supplement and in feeder-free conditions for potential therapeutic uses
Strength training in elderly: An useful tool against sarcopenia
The loss of muscle mass and strength in elderly population (especially after the age of 65-70) represents a public health problem. Due to the high prevalence of frailty in older adults, cardiovascular or low-intensity exercise is implemented as first choice option. Although beneficial these training schemes are not as effective as strength-based resistance training for increasing muscle strength and hypertrophy. In fact, when performed progressively and under professional supervision, strength-based training has been proposed as an important and valid methodology to reduce sarcopenia-related problems. In this mini-review, we not only summarize the benefits of weight resistance training but also highlight practical recommendations and other non-conventional methods (e.g., suspension training) as part of an integral anti-sarcopenia strategy. Future directions including cluster set configurations and high-speed resistance training are also outlined
A Stimulated Raman Loss spectrometer for metrological studies of quadrupole lines of hydrogen isotopologues
We discuss layout and performance of a high-resolution Stimulated Raman Loss
spectrometer that has been newly developed for accurate studies of spectral
lineshapes and line center frequencies of hydrogen isotopologues and in general
of Raman active transitions. Thanks to the frequency comb calibration of the
detuning between pump and Stokes lasers and to an active alignment of the two
beams, the frequency accuracy is well below 100 kHz. Over the vertical axis the
spectrometer benefits from shot-noise limited detection, signal enhancement via
multipass cell, active flattening of the spectral baseline and measurement
times of few seconds over spectral spans larger than 10 GHz. Under these
conditions an efficient averaging of Raman spectra is possible over long
measurement times with minimal distortion of spectral lineshapes. By changing
the pump laser, transitions can be covered in a very broad frequency span, from
50 to 5000 , including both vibrational and rotational bands.
The spectrometer has been developed for studies of fundamental and collisional
physics of hydrogen isotopologues and has been recently applied to the
metrology of the Q(1) 1-0 line of
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