209 research outputs found
Beyond-dipole approximation effects in photoionization: importance of the photon momentum
No full textIn most of the past studies of processes involving interaction of lasers with atoms and molecules the tiny photon momentum has not been taken into account nor the issue of momentum sharing between a photoelectron and an ion has not been addressed despite the fact than when intense lasers are used a huge amount of infrared photons are absorbed. This situation has been related to the fact that in most theoretical investigations the dipole approximation has been used for description of the photoionization processes. In this talk I emphasize the importance of using the non-dipole approaches in description of the interaction of intense lasers with atoms and molecules. I will review some surprising results obtained by us using numerical solutions of the time-dependent Schroedinger equation in [1-3] and present new results related to the photon-momentum effect using counter-propagating pulses and the specific non-dipole effects in diatomic molecules.
[1] S. Chelkowski, A.D. Bandrauk, and P.B. Corkum, Phys.Rev.Let. 113, 263005 (2014).
[2] S. Chelkowski, A.D. Bandrauk, and P.B. Corkum, Phys.Rev. A 92, 051401 (R) (2015).
[3] S. Chelkowski, A.D. Bandrauk, and P.B. Corkum, Phys.Rev. A 95, 053402 (2017).Non UBCUnreviewedAuthor affiliation: Université de SherbrookeOthe
Triple Michelson interferometer for a third-generation gravitational wave detector
No full textThe upcoming European design study 'Einstein gravitational-wave Telescope' represents the first step towards a substantial, international effort for the design of a third-generation interferometric gravitational wave detector. It is generally believed that third-generation instruments might not be installed into existing infrastructures but will provoke a new search for optimal detector sites. Consequently, the detector design could be subject to fewer constraints than the on-going design of the second-generation instruments. In particular, it will be prudent to investigate alternatives to the traditional L-shaped Michelson interferometer. In this paper, we review an old proposal to use three Michelson interferometers in a triangular configuration. We use this example of a triple Michelson interferometer to clarify the terminology and will put this idea into the context of more recent research on interferometer technologies. Furthermore, the benefits of a triangular detector will be used to motivate this design as a good starting point for a more detailed research effort towards a third-generation gravitational-wave detector. © 2009 IOP Publishing Ltd
Optical detector topology for third-generation gravitational wave observatories
No full textThe third generation of gravitational wave observatories, with the aim of providing 100 times better sensitivity than currently operating interferometers, is expected to establish the evolving field of gravitational wave astronomy. A key element, required to achieve this ambitious sensitivity goal, is the exploration of new interferometer geometries, topologies and configurations. In this article we review the current status of the ongoing design work for third-generation gravitational wave observatories. The main focus is the evaluation of the detector geometry and detector topology. In addition we discuss some promising detector configurations and potential noise reduction schemes
Adapting authoritarianism: institutions and co-optation in Egypt and Syria
No full textThis PhD thesis compares Egypt and Syria’s authoritarian political systems. While the tendency in social science political research treats Egypt and Syria as similarly authoritarian, this research emphasizes differences between the two systems with special reference to institutions and co-optation. Rather than reducibly understanding Egypt and Syria as sharing similar histories, institutional arrangements, or ascribing to the oft-repeated convention that “Syria is Egypt but 10 years behind,” this thesis focuses on how events and individual histories shaped each states current institutional strengthens and weaknesses. Specifically, it explains the how varying institutional politicization or de-politicization affects each state’s capabilities for co-opting elite and non-elite individuals.
Beginning with a theoretical framework that considers the limited utility of democratization and transition theoretical approaches, the work underscores the persistence and durability of authoritarianism. Chapter two details the politicized institutional divergence between Egypt and Syria that began in the 1970s. Chapter three and four examines how institutional politicization or de-politicization affects elite and non-elite individual co-optation in Egypt and Syria. Chapter five discusses the study’s general conclusions and theoretical implications.
This thesis’s argument is that Egypt and Syria co-opt elites and non-elites differently because of the varying degrees of institutional politicization in each governance system. Rather than view one country as more politically developed than the other, this work argues that Syria’s political institutions are more politicized than their Egyptian counterparts. Syria’s political arena is, thus, described as politicized-patrimonialism. Syria’s politicized-patrimonial arena produces uneven co-optation of elites and non-elites as they are diffused through competing institutions. Conversely, the Egyptian political arena remains highly personalized as weak institutions and individuals are manipulated and molded according to the president’s ruling clique. This is referred to as personalized-patrimonialism. As a consequence, Egypt’s political establishment demonstrates more flexibility in ad hoc altering and adapting its arena depending on the emergence of crises.
This study’s theoretical implications suggest that, contrary to modernization and democratization theory’s adage that institutions lead to a political development, politicized institutions within a patrimonial order actually hinder regime adaptation because consensus is harder to achieve and maintain. It is within this context that Egypt’s de-politicized institutional framework advantages its top political elite. In this reading of Egyptian and Syrian politics, Egypt’s personalized political arena is more adaptable than Syria’s. These conclusions do not indicate that political reform is a process underway in either state
Action du champ magnétique sur la perméabilité diélectrique des liquides polaires
No full textVariations of the dielectric permittivity of nitrobenzene in an intense magnetic field were found with a circuit capable of detecting Δε ~ 10-6. The measurements were carried out by the method of magnetic field strength differences, in order to reduce heating of the condenser by eddy currents. The field was varied from H 0 = ca. 30 kOe to H0 + h = ca. 40 kOe. The results of measurements were converted to ΔεH corresponding to a rise in magnetic field strength from 0 to 40 kOe. This latter variation ΔεH, in the case of nitrobenzene, was found to represent an increase in dielectric permittivity of 3.9 x 10-6, in very good agreement with the theoretical calculations of A. Piekara and S. Kielich for a local electric field of the Onsager type.On a trouvé des variations de la perméabilité diélectrique du nitrobenzène soumis à l'influence d'un champ magnétique intense, en utilisant une méthode dont la sensibilité permettait de déceler Δε ~ 10-6. Afin de réduire l'échauffement du condensateur par les courants de Foucault, les mesures furent effectuées par un procédé consistant à faire croître le champ magnétique, en commençant par une valeur H0 (de 30 kOe environ) jusqu'à une valeur H 0 + h (de 40 kOe environ). Les résultats ont été recalculés pour obtenir la variation ΔεH correspondant à un accroissement du champ de 0 à 40 kOe. Cette variation ΔεH, dans le cas du nitrobenzène, se présente sous la forme d'une augmentation de la perméabilité diélectrique de 3,9 x 10-5, en très bon accord avec les calculs théoriques effectués par A. Piekara et S. Kielich, admettant l'existence d'un champ électrique interne du type d'Onsager
Measuring molecular wave functions using laser Coulomb explosion imaging with ultraviolet lasers
No full textA high-frequency laser (\u3bb<40 nm) can ionize the H2\u207a molecule via a one-photon transition to the electron\u2013nuclei continua. From exact non-Born\u2013Oppenheimer simulations of dynamics of H2\u207a in intense laser fields we show that it is possible to reconstruct the shape of the initial, stationary vibrational wave function |\u3c8\u1d65(R)|\ub2 by measuring kinetic energy spectra of either protons or electrons. The reconstruction procedure from proton spectra is based on a perturbative one-photon transition to the electron\u2013proton continua and formally is similar to the previously discussed laser Coulomb explosion imaging technique. For sufficiently high explosion energy, proton spectra are directly proportional to |\u3c8\u1d65(q\ub2/E\u2099)|\ub2, where E\u2099 is the nuclear energy. Alternatively, one can measure kinetic energy of electrons, from which the proton energy can be deduced via the conservation of energy for a one-photon transition to the electron\u2013proton continuum, and thus the shape of the first peak in the electron spectrum is also directly proportional to the initial vibrational probability distribution. We compare these two methods and also compare them with the previously proposed imaging methods based on Coulomb explosions induced by multiphoton transitions. We find that high-frequency lasers allow us to perform the imaging of a stationary wave function with longer and less intense pulses than pulses required in the previously discussed long-wavelength regime. Imaging based on electron spectra requires longer pulses, since the spread of photon energy in short pulses does not allow us to determine nuclear energy, in an accurate way, via conservation of energy. In general, the photo-electron spectra from H2\u207a are found to be very different from atomic spectra, the latter having much narrower peaks, while the former are greatly enlarged due to sharing the final energy with nuclei. The photo-electron and nuclear spectra show a very clear imprint of the nuclear wave function, e.g. if the molecule is prepared in the v-state that has v nodes, both spectra will also have v nodes.Peer reviewed: YesNRC publication: N
Coherent propagation of intense ultrashort laser pulses in a molecular multilevel medium
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