Localized buckling in sandwich struts with inhomogeneous deformation in both face plates

A nonlinear analytical model for investigating localized interactive buckling in simply supported thin-face plate sandwich struts with weak cores is extended to account for local deformations in both face plates, which have been observed in experiments and finite element simulations. The original model is based on potential energy principles with large displacement assumptions. It assumes Timoshenko shear deformable theory for the core and approximates the overall mode as a half-sine wave along the length of the strut while the local face plate displacements are initially unknown and are found as solutions of the governing equations. The extended model is able to capture measurable local face plate displacements in the less compressed face plate, beyond the secondary bifurcation which leads to localized interactive buckling, for the case where overall buckling is critical. Moreover, the allowance of local displacements in both face plates allows the extended model to predict the post-buckling behavior better in cases where local buckling is critical. The results from this model compare very well with nonlinear finite element simulations with respect to both the equilibrium paths and panel deformations

Coherent population trapping in ruby crystal at room temperature

Observation of coherent population trapping (CPT) at ground-state Zeeman sublevels of $Cr^{3+}$-ion in ruby is reported. The experiments are performed at room temperature by using both nanosecond optical pulses and nanosecond trains of ultrashort pulses. In both cases sharp drops in the resonantly induced fluorescence are detected as the external magnetic field is varied. Theoretical analysis of CPT in a transient regime due to pulsed action of optical pulses is presented.Comment: 4 pages, 4 figures, submitted to PR

Coherent Patterning of Matter Waves with Subwavelength Localization

We propose the Subwavelength Localization via Adiabatic Passage (SLAP) technique to coherently achieve state-selective patterning of matter waves well beyond the diffraction limit. The SLAP technique consists in coupling two partially overlapping and spatially structured laser fields to three internal levels of the matter wave yielding state-selective localization at those positions where the adiabatic passage process does not occur. We show that by means of this technique matter wave localization down to the single nanometer scale can be achieved. We analyze in detail the potential implementation of the SLAP technique for nano-lithography with an atomic beam of metastable Ne* and for coherent patterning of a two-component 87Rb Bose-Einstein condensate.Comment: 6 pages, 5 figure

Dark States and Coherent Control of Spin States in Molecular Magnets

We propose a scheme to realize coherent control of spin states of molecule magnet, Ni$_4$. We introduce transverse magnetic fields with special frequencies. When the frequencies of transverse magnetic fields match in some conditions, we obtain dark states in Ni$_4$ molecules. Through adjusting the magnitude of magnetic fields, we can obtain any arbitrary superposition of the two ground spin states of Ni$_4$ molecules.Comment: 7 pages, 4 figures. To appear in Physical Review

Time-resolved pump-probe spectroscopy with spectral domain ghost imaging

An atomic-level picture of molecular and bulk processes, such as chemical bonding and charge transfer, necessitates an understanding of the dynamical evolution of these systems. On the ultrafast timescales associated with nuclear and electronic motion, the temporal behaviour of a system is often interrogated in a 'pump-probe' scheme. Here, an initial 'pump' pulse triggers dynamics through photoexcitation, and after a carefully controlled delay a 'probe' pulse initiates projection of the instantaneous state of the evolving system onto an informative measurable quantity, such as electron binding energy. In this paper, we apply spectral ghost imaging to a pump-probe time-resolved experiment at an X-ray free-electron laser (XFEL) facility, where the observable is spectral absorption in the X-ray regime. By exploiting the correlation present in the shot-to-shot fluctuations in the incoming X-ray pulses and measured electron kinetic energies, we show that spectral ghost imaging can be applied to time-resolved pump-probe measurements. In the experiment presented, interpretation of the measurement is simplified because spectral ghost imaging separates the overlapping contributions to the photoelectron spectrum from the pump and probe pulse

Inner Valence Hole Migration in Isopropanol

Even within the sudden approximation, the removal of one neutral Hartree-Fock orbital does not leave the molecule in a pure one-hole state of the cation; coupling to virtual orbitals leads to a breakdown in the molecular orbital picture. This can be understood as interaction with two-hole one-particle states (singly excited cations) and becomes significant when those states are energetically similar to the one-hole states. This splitting of states is most relevant for inner valence holes which lie above the double ionisation potential. As such, impulsive creation of an inner valence hole (IVH) wavepacket results in a time dependent charge density which is purely electronic in nature (charge migration) [1] , [2] , though it depends on the nuclear geometry at the time of excitation, and subsequent nuclear motion will result in decoherence [3]

Buffer-gas induced absorption resonances in Rb vapor

We observe transformation of the electromagnetically induced transparency (EIT) resonance into the absorption resonance in a $\Lambda$ interaction configuration in a cell filled with $^{87}$Rb and a buffer gas. This transformation occurs as a one-photon detuning of the coupling fields is varied from the atomic transition. No such absorption resonance is found in the absence of a buffer gas. The width of the absorption resonance is several times smaller than the width of the EIT resonance, and the changes of absorption near these resonances are about the same. Similar absorption resonances are detected in the Hanle configuration in a buffered cell.Comment: 11 pages, 15 figures; 13 pages, 17 figures, added numerical simulatio

Delivery of stable ultra-thin liquid sheets in vacuum for biochemical spectroscopy

The development of ultra-thin flat liquid sheets capable of running in vacuum has provided an exciting new target for X-ray absorption spectroscopy in the liquid and solution phases. Several methods have become available for delivering in-vacuum sheet jets using different nozzle designs. We compare the sheets produced by two different types of nozzle; a commercially available borosillicate glass chip using microfluidic channels to deliver colliding jets, and an in-house fabricated fan spray nozzle which compresses the liquid on an axis out of a slit to achieve collision conditions. We find in our tests that both nozzles are suitable for use in X-ray absorption spectroscopy with the fan spray nozzle producing thicker but more stable jets than the commercial nozzle. We also provide practical details of how to run these nozzles in vacuum

Role of electromagnetically induced transparency in resonant four-wave-mixing schemes.

Published versio

Optical imaging beyond the diffraction limit via dark states

We study the possibility of creating spatial patterns having subwavelength size by using the so-called dark states formed by the interaction between atoms and optical fields. These optical fields have a specified spatial distribution. Our experiments in Rb vapor display spatial patterns that are smaller than the length determined by the diffraction limit of the optical system used in the experiment. This approach may have applications to interference lithography and might be used in coherent Raman spectroscopy to create patterns with subwavelength spatial resolution.Comment: 5 pages, 5 figure