We study the temperature dependence of the underlying mechanisms related to the signal strength and imaging depth in photoacoustic imaging. The presented theoretical and experimental results indicate that imaging depth can be improved by lowering the temperature of the intermediate medium that the laser passes through to reach the imaging target. We discuss the temperature dependency of optical and acoustic properties of the intermediate medium and their changes due to cooling. We demonstrate that the SNR improvement of the photoacoustic signal is mainly due to the reduction of Grüneisen parameter of the intermediate medium which leads to a lower level of background noise. These findings may open new possibilities toward the application of biomedical laser refrigeration.
The variation of the work function upon carbon adsorption on the reconstructed Au(110) surface is measured experimentally and compared to density functional calculations. The adsorption dynamics is simulated with ab-initio molecular dynamics techniques. The contribution of various energetically available adsorption sites on the deposition process is analyzed, and the work function behavior with carbon coverage is explained by the resultant electron charge density distributions. arXiv:1805.06931v1 [physics.atom-ph]
An accurate 3D numerical scheme for the De Broglie-Bohm's framework of Bohmian mechanics is presented. This method is utilized to explore the sub-cycle multiphoton ionization dynamics of the hydrogen atom subject to intense near infrared (NIR) laser fields on the subfemtosecond time scale. The analysis of the time-dependent electron density reveals that several distinct density portions can be shaped and detached from the core within a half cycle of the laser field. As a complementary perspective, we identify several distinct groups of the Bohmian trajectories which represent the multiple detachments of the electron density at different times. The method presented provides very accurate electron densities and Bohmian trajectories that allow to uncover the origin of the formation of the transient and distinct electron structures seen in the MPI processes. The recent development of attosecond metrology has enabled the real-time experimental observation of ultrafast electron dynamics in atomic and molecular systems [1,2]. Considerable interest has been recently paid also to the study of transient absorption spectroscopy in ultrafast time domain [3-5]. For example, the observation of the transient changes in the absorption of an isolated attosecond XUV pulse by helium atoms in the presence of a delayed few-cycle NIR laser pulse has been recently reported and uncovered novel absorption structures corresponding to laser-induced "virtual" intermediate states in the two-color two-photon (XUV + NIR) and three photon (XUV+ NIR + NIR) absorption processes [5]. These previously unobserved absorption structures are modulated on half-cycle (~1.3 fs) and quarter-cycle (~0.6 fs) time scales, resulting from quantum optical interference in the laser-driven atom. More recently, there is also new interest in the study of sub-cycle transient high harmonic generation (HHG)
We propose a graph-theoretical formalism to study generic circuit quantum electrodynamics systems consisting of a two level qubit coupled with a single-mode resonator in arbitrary coupling strength regimes beyond rotating-wave approximation. We define colored-weighted graphs, and introduce different products between them to investigate the dynamics of superconducting qubits in transverse, longitudinal, and bidirectional coupling schemes. The intuitive and predictive picture provided by this method, and the simplicity of the mathematical construction, are demonstrated with some numerical studies of the multiphoton resonance processes and quantum interference phenomena for the superconducting qubit systems driven by intense ac fields.
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