475 research outputs found
ExoMol line lists -- LIII: Empirical Rovibronic spectra of Yttrium Oxide (YO)
Empirical line lists for the open shell molecule YO (yttrium
oxide) and its isotopologues are presented. The line lists cover the 6 lowest
electronic states: , , , , and up to 60000 cm
( m) for rotational excitation up to . An \textit{ab
initio} spectroscopic model consisting of potential energy curves (PECs),
spin-orbit and electronic angular momentum couplings is refined by fitting to
experimentally determined energies of YO, derived from published YO
experimental transition frequency data. The model is complemented by empirical
spin-rotation and -doubling curves and \textit{ab initio} dipole
moment and transition dipole moment curves computed using MRCI. The \textit{ab
initio} PECs computed using the complete basis set limit extrapolation and the
CCSD(T) method with its higher quality provide an excellent initial
approximation for the refinement. Non-adiabatic coupling curves for two pairs
of states of the same symmetry / and / are computed using a
state-averaged CASSCF and used to built diabatic representations for the , , and
curves. Calculated lifetimes of YO are tuned to agree well with the experiment,
where available. The BRYTS YO line lists for are included into the ExoMol data
base (www.exomol.com)
Flat liquid jet as a highly efficient source of terahertz radiation
Polar liquids are strong absorbers of electromagnetic waves in the terahertz range, therefore, historically such liquids have not been considered as good candidates for terahertz sources. However, flowing liquid medium has explicit advantages, such as a higher damage threshold compared to solid-state sources and more efficient ionization process compared to gases. Here we report systematic study of efficient generation of terahertz radiation in flat liquid jets under sub-picosecond single-color optical excitation. We demonstrate how medium parameters such as molecular density, ionization energy and linear absorption contribute to the terahertz emission from the flat liquid jets. Our simulation and experimental measurements reveal that the terahertz energy has quasi-quadratic dependence on the optical excitation pulse energy. Moreover, the optimal pump pulse duration, which depends on the thickness of the jet is theoretically predicted and experimentally confirmed. The obtained optical-to-terahertz energy conversion efficiency is more than 0.05%. It is comparable to the commonly used optical rectification in most of electro-optical crystals and two-color air filamentation. These results, significantly advancing prior research, can be successfully applied to create a new alternative source of terahertz radiation
Solving the Simplest Theory of Quantum Gravity
We solve what is quite likely the simplest model of quantum gravity, the
worldsheet theory of an infinitely long, free bosonic string in Minkowski
space. Contrary to naive expectations, this theory is non-trivial. We
illustrate this by constructing its exact factorizable S-matrix. Despite its
simplicity, the theory exhibits many of the salient features expected from more
mature quantum gravity models, including the absence of local off-shell
observables, a minimal length, a maximum achievable (Hagedorn) temperature, as
well as (integrable relatives of) black holes. All these properties follow from
the exact S-matrix. We show that the complete finite volume spectrum can be
reconstructed analytically from this S-matrix with the help of the
thermodynamic Bethe Ansatz. We argue that considered as a UV complete
relativistic two-dimensional quantum field theory the model exhibits a new type
of renormalization group flow behavior, "asymptotic fragility". Asymptotically
fragile flows do not originate from a UV fixed point.Comment: 32+4 pages, 1 figure, v2: typos fixed, published versio
Boundary RG Flow Associated with the AKNS Soliton Hierarchy
We introduce and study an integrable boundary flow possessing an infinite
number of conserving charges which can be thought of as quantum counterparts of
the Ablowitz, Kaup, Newell and Segur Hamiltonians. We propose an exact
expression for overlap amplitudes of the boundary state with all primary states
in terms of solutions of certain ordinary linear differential equation. The
boundary flow is terminated at a nontrivial infrared fixed point. We identify a
form of whole boundary state corresponding to this fixed point.Comment: 54 page
Double-pump technique – one step closer towards efficient liquid-based THz sources
By irradiating a water jet with double pulses, we demonstrate 4-fold higher THz wave generation than for a single pump pulse. The dependence of the enhanced THz signal on the temporal delay between two collinear pulses reveals the optimal time for launching signal pulse is near 2-4 ps, which corresponds to the time needed to create the complete pre-ionization state when sufficient electron density is already induced, and there is no plasma reflection of the pump pulse radiation. The increase in THz waves generation efficiency corresponds to the case of water jet excitation by the pulses with an optimal duration for a certain jet thickness, which is determined by the spatial pulse size. Using a theoretical model of the interaction of a high-intensity sub-picosecond pulse with an isotropic medium, we held a numerical simulation, which well describes the experimental results when using 3 ps value of population relaxation time. Thus, in this work, double pump method allows not only to increase the energy of the generated THz waves, but also to determine the characteristic excited state lifetime of liquid water. The optical-to-terahertz conversion efficiency in case of double pulse excitation of water column is of the order of 0.5·10−3, which exceeds the typical values for THz waves generation during two-color filamentation in air and comparable with the achievable values due to the optical rectification in some crystals
The Degenerate Parametric Oscillator and Ince's Equation
We construct Green's function for the quantum degenerate parametric
oscillator in terms of standard solutions of Ince's equation in a framework of
a general approach to harmonic oscillators. Exact time-dependent wave functions
and their connections with dynamical invariants and SU(1,1) group are also
discussed.Comment: 10 pages, no figure
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