129 research outputs found
Simulated XUV Photoelectron Spectra of THz-pumped Liquid Water
Highly intense, sub-picosecond terahertz (THz) pulses can be used to induce
ultrafast temperature jumps (T-jumps) in liquid water. A supercritical state of
gas-like water with liquid density is established, and the accompanying
structural changes are expected to give rise to time-dependent chemical shifts.
We investigate the possibility of using extreme ultraviolet (XUV) photoelectron
spectroscopy as a probe for ultrafast dynamics induced by sub-picosecond THz
pulses of varying intensities and frequencies. To this end, we use ab initio
methods to calculate photoionization cross sections and photoelectron energies
of (H2O) clusters embedded in an aqueous environment represented by
point charges. The cluster geometries are sampled from ab initio molecular
dynamics simulations modeling the THz-water interactions. We find that the
peaks in the valence photoelectron spectrum are shifted by up to 0.4 eV after
the pump pulse, and that they are broadened with respect to unheated water. The
shifts can be connected to structural changes caused by the heating, but due to
saturation effects they are not sensitive enough to serve as a thermometer for
T-jumped water
Limitations to THz generation by optical rectification using tilted pulse fronts
Terahertz (THz) generation by optical rectification (OR) using
tilted-pulse-fronts is studied. One-dimensional (1-D) and 2-D spatial models,
which simultaneously account for (i) the nonlinear coupled interaction of the
THz and optical radiation, (ii) angular and material dispersion, (iii)
absorption, iv) self-phase modulation and (v) stimulated Raman scattering are
presented. We numerically show that the large experimentally observed cascaded
frequency down-shift and spectral broadening (cascading effects) of the optical
pump pulse is a direct consequence of THz generation. In the presence of this
large spectral broadening, the phase mismatch due to angular dispersion is
greatly enhanced. Consequently, this cascading effect in conjunction with
angular dispersion is shown to be the strongest limitation to THz generation in
lithium niobate for pumping at 1 micron. It is seen that the exclusion of these
cascading effects in modeling OR, leads to a significant overestimation of the
optical-to-THz conversion efficiency. The simulation results are supported by
experiments
Direct laser acceleration of electrons in free-space
Compact laser-driven accelerators are versatile and powerful tools of
unarguable relevance on societal grounds for the diverse purposes of science,
health, security, and technology because they bring enormous practicality to
state-of-the-art achievements of conventional radio-frequency accelerators.
Current benchmarking laser-based technologies rely on a medium to assist the
light-matter interaction, which impose material limitations or strongly
inhomogeneous fields. The advent of few cycle ultra-intense radially polarized
lasers has materialized an extensively studied novel accelerator that adopts
the simplest form of laser acceleration and is unique in requiring no medium to
achieve strong longitudinal energy transfer directly from laser to particle.
Here we present the first observation of direct longitudinal laser acceleration
of non-relativistic electrons that undergo highly-directional multi-GeV/m
accelerating gradients. This demonstration opens a new frontier for direct
laser-driven particle acceleration capable of creating well collimated and
relativistic attosecond electron bunches and x-ray pulses
Long-term Hybrid Stabilization of the Carrier-Envelope Phase
Controlling the carrier envelope phase (CEP) in mode-locked lasers over
practically long timescales is crucial for real-world applications in ultrafast
optics and precision metrology. We present a hybrid solution that combines a
feed-forward technique to stabilize the phase offset in fast timescales and a
feedback technique that addresses slowly varying sources of interference and
locking bandwidth limitations associated with gain media with long upper-state
lifetimes. We experimentally realize the hybrid stabilization system in an
Er:Yb:glass mode-locked laser and demonstrate 75 hours of stabilization with
integrated phase noise of 14 mrad (1 Hz to 3 MHz), corresponding to around 11
as of carrier to envelope jitter. Additionally, we examine the impact of
environmental factors, such as humidity and pressure, on the long-term
stability and performance of the system.Comment: 11 pages, 6 figures, 1 table; to be published in Optics Express;
revisions include adjustment of some citations, additions to section 2, and
added information in table
Design, Optimization, and Blackbox Optimization of Laser Systems
Chirped pulse amplification (CPA) and subsequent nonlinear optical (NLO)
systems constitute the backbone of myriad advancements in semiconductor and
additive manufacturing, communication networks, biology and medicine, defense
and national security, and a host of other sectors over the past decades.
Accurately and efficiently modeling CPA and NLO-based laser systems is
challenging because of the multitude of coupled linear and nonlinear processes
and high variability in simulation frameworks. The lack of fully-integrated
models severely hampers further advances in tailoring existing or materializing
new CPA+NLO systems. Such tools are the key to enabling emerging optimization
and inverse design approaches reliant on data-driven machine learning methods.
Here, we present a modular start-to-end software model encompassing an array of
amplifier designs and nonlinear optics techniques. The simulator renders time-
and frequency-resolved electromagnetic fields alongside essential physical
characteristics of energy, fluence, and spectral distribution. To demonstrate
its robustness and real-world applicability -- specifically, reverse
engineering, system optimization, and inverse design -- we present a case study
on the LCLS-II photo-injector laser, representative of a high-power and
spectro-temporally non-trivial CPA+NLO system
Laser-Induced Linear Electron Acceleration in Free Space
Linear acceleration in free space is a topic that has been studied for over
20 years, and its ability to eventually produce high-quality, high energy
multi-particle bunches has remained a subject of great interest. Arguments can
certainly be made that such an ability is very doubtful. Nevertheless, we chose
to develop an accurate and truly predictive theoretical formalism to explore
this remote possibility in a computational experiment. The formalism includes
exact treatment of Maxwell's equations, exact relativistic treatment of the
interaction among the multiple individual particles, and exact treatment of the
interaction at near and far field. Several surprising results emerged. For
example, we find that 30 keV electrons (2.5% energy spread) can be accelerated
to 7.7 MeV (2.5% spread) and to 205 MeV (0.25% spread) using 25 mJ and 2.5 J
lasers respectively. These findings should hopefully guide and help develop
compact, high-quality, ultra-relativistic electron sources, avoiding
conventional limits imposed by material breakdown or structural constraints.Comment: Supplementary Information starts on pg 1
Primeras luces de un espectroscopio impreso en 3D
La espectroscopía aplicada a la astronomía es una de las técnicas más potentes que tenemos para poder estudiar la naturaleza física de los astros. Esta técnica nos ha permitido, entre otras cosas, poder determinar la composición química de las fotosferas estelares, la detección de exoplanetas y es la técnica que nos ha permitido poder medir la expansión del universo. Al tratarse de una técnica tan potente los miembros del Grupo Universitario de Astronomía decidimos iniciarnos en esta técnica
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