Phase Space Methods

Including non-zero initial momenta for ejected electrons in strong infrared laser fields is further developed [compare Ristic et al. 2007]. It has been stressed that, apart from being natural, the including non-zero initial momenta enables one to go into deeper analysis of the process of tunnel ionization of atoms in strong laser fields (intensity up to 10^16 W/cm^2). It is indicated that all electrons that could be ejected, under the circumstances, are ejected at field intensity sim 10^13 W/cm^2, and that the effect of ionization after that is strongly diminished, which can be seen from the slope of the plates on Fig. 2. This, also, explains the saturation effect for the fields up to 10^16 W/cm^2 (Ristic et al. 2006, Ristic and Stefanovic 2007, Ristic et al. 1998, Milosevic et al. 2002), and probably this saturation goes on until the fields raising relativistic effects sim 10^18 W/cm^2 (Milosevic et al. 2002). Opposite to what was believed earlier (Milosevic et al. 2002), that atom...

We study a generalization of the Kibble-Slepian (KS) expansion formula in 3 dimensions. The generalization is obtained by replacing the Hermite polynomials by the q−Hermite ones. If such a replacement would lead to non-negativity for all allowed values of parameters and for all values of variables ranging over certain Cartesian product of compact intervals then we would deal with a generalization of the 3 dimensional Normal distribution. We show that this is not the case. We indicate some values of the parameters and some compact set in R 3 of positive measure, such that the values of the extension of KS formula are on this set negative. Nevertheless we indicate other applications of so generalized KS formula. Namely we use it to sum certain kernels built of the Al-Salam-Chihara polynomials for the cases that were not considered by other authors. One of such kernels sums up to the Askey-Wilson density disclosing its new, interesting properties. In particular we are able to obtain a generalization of the 2 dimensional Poisson-Mehler formula. As a corollary we indicate some new interesting properties of the Askey-Wilson polynomials with complex parameters. We also pose several open questions.

Phase spaces are different ways to represent signals. Owing to their properties, they are often used for signal compression and recognition with high discrimination abilities. We present several recently introduced Wigner-related sets of representations that have improved signal processing performance, and we introduce an optical implementation. This study deals with the generalized Wigner spaces, the fractional Fourier transform, and the xp and the rp representations. The optical implementations are demonstrated and discussed.

The Photo Injector Test facility at DESY, Zeuthen site (PITZ), is dedicated to develop and optimize high brightness electron sources for short wavelength Free-Electron Lasers (FELs) like FLASH and the European XFEL, both in Hamburg (Germany). Since October 2009 a major upgrade is ongoing with the goal to improve the accelerating components, the photocathode drive laser system and the beam diagnostics as well. The essential new feature in the running will be an in-vacuum 10 MW RF directional coupler to be used for the RF monitoring and control. In this context a significant improvement of the RF stability is expected. RF pulses of 800 microseconds with 10 Hz repetition rate will be used. The most important upgrade of the diagnostics system will be the implementation of a phase space tomography module (PST) consisting of three FODO cells each surrounded by two screen stations. The goal is an improved measurement of the transverse phase space at different charge levels. The upgraded facility will be described.

We study generalization of Kible-Slepian (K-S) expansion formula in 3 dimensions. The generalization is obtained by replacing in K-S formula Hermite polynomials by q−Hermite ones. If such replacement would lead to non-negativity of values for all allowed values of parameters and for values of variables from certain Cartesian product of compact intervals then we would deal with generalization of 3 dimensional normal distribution. We show that this is not the case. We indicate some values of parameters and some compact set in R 3 of positive measure, such that values of the extension K-S formula are on this set negative. Nevertheless we indicate other applications of so generalized K-S formula, namely we use this formula to sum certain kernels built of Al-Salam-Chihara polynomials for cased that were not considered by other authors. One of such kernels sum up to Askey-Wilson density. Hence we are able to obtain generalization of 2 dimensional Poisson-Mehler formula. We also pose several open questions.

We examine the phase space structures that govern reaction dynamics in the absence of critical points on the potential energy surface. We show that in the vicinity of hyperbolic invariant tori, it is possible to define phase space dividing surfaces that are analogous to the dividing surfaces governing transition from reactants to products near a critical point of the potential energy surface. We investigate the problem of capture of an atom by a diatomic molecule and show that a normally hyperbolic invariant manifold exists at large atom-diatom distances, away from any critical points on the potential. This normally hyperbolic invariant manifold is the anchor for the construction of a dividing surface in phase space, which defines the outer or loose transition state governing capture dynamics. We present an algorithm for sampling an approximate capture dividing surface, and apply our methods to the recombination of the ozone molecule. We treat both 2 and 3 degrees of freedom models ...

We present a semiclassical two-step model for strong-field ionization that accounts for path interferences of tunnel-ionized electrons in the ionic potential beyond perturbation theory. Within the framework of a classical trajectory Monte-Carlo representation of the phase-space dynamics, the model employs the semiclassical approximation to the phase of the full quantum propagator in the exit channel. By comparison with the exact numerical solution of the time-dependent Schrödinger equation for strong-field ionization of hydrogen, we show that for suitable choices of the momentum distribution after the first tunneling step, the model yields good quantitative agreement with the full quantum simulation. The two-dimensional photoelectron momentum distributions, the energy spectra, and the angular distributions are found to be in good agreement with the corresponding quantum results. Specifically, the model quantitatively reproduces the fan-like interference patterns in the low-energy part of the two-dimensional momentum distributions as well as the modulations in the photoelectron angular distributions.

For biaxial stretching strain paths, which are typically encountered in sheet metal forming, the stress triaxiality ranges from 0.33 to 0.67. At this low level of triaxiality, voids change their shape from spherical to general spheroidal shape. In the literature, unit cell studies show the dependency of void shape on the lode parameter, especially at low stress triaxiality. Several authors also pointed out the influence of lode parameter on ductile failure. In the current study, lode parameter dependent Gurson-based models are combined with bifurcation analysis for the prediction of formability limits of TRIP780 steel sheet. Moreover, Thomason's coalescence criterion is considered for the prediction of critical porosity. For the anisotropic plastic behavior of the dense material, the quadratic Hill'48 yield surface is considered. Contribution to porosity evolution due to shear mechanism is also analyzed. In addition, the effect of lode parameter on the prediction of forming limit diagram (FLD) is investigated. It is observed that the accelerated evolution of porosity, due to the consideration of lode parameter, induces lower ductility limits for the modified Gurson-based model, as compared to the original Gurson model. The results also demonstrate that the use of the Thomason coalescence criterion for the determination of critical porosity plays an important role in the prediction of FLDs, as compared to fixed critical porosity used in the GursonTvergaardNeedleman model.

For biaxial stretching strain paths, which are typically encountered in sheet metal forming, the stress triaxiality ranges from 0.33 to 0.67. At this low level of triaxiality, voids change their shape from spherical to general spheroidal shape. In the literature, unit cell studies show the dependency of void shape on the lode parameter, especially at low stress triaxiality. Several authors also pointed out the influence of lode parameter on ductile failure. In the current study, lode parameter dependent Gurson-based models are combined with bifurcation analysis for the prediction of formability limits of TRIP780 steel sheet. Moreover, Thomason's coalescence criterion is considered for the prediction of critical porosity. For the anisotropic plastic behavior of the dense material, the quadratic Hill'48 yield surface is considered. Contribution to porosity evolution due to shear mechanism is also analyzed. In addition, the effect of lode parameter on the prediction of forming limit diagram (FLD) is investigated. It is observed that the accelerated evolution of porosity, due to the consideration of lode parameter, induces lower ductility limits for the modified Gurson-based model, as compared to the original Gurson model. The results also demonstrate that the use of the Thomason coalescence criterion for the determination of critical porosity plays an important role in the prediction of FLDs, as compared to fixed critical porosity used in the GursonTvergaardNeedleman model.

We present a semiclassical two-step model for strong-field ionization that accounts for path interferences of tunnel-ionized electrons in the ionic potential beyond perturbation theory. Within the framework of a classical trajectory Monte-Carlo representation of the phase-space dynamics, the model employs the semiclassical approximation to the phase of the full quantum propagator in the exit channel. By comparison with the exact numerical solution of the time-dependent Schrödinger equation for strong-field ionization of hydrogen, we show that for suitable choices of the momentum distribution after the first tunneling step, the model yields good quantitative agreement with the full quantum simulation. The two-dimensional photoelectron momentum distributions, the energy spectra, and the angular distributions are found to be in good agreement with the corresponding quantum results. Specifically, the model quantitatively reproduces the fan-like interference patterns in the low-energy part of the two-dimensional momentum distributions as well as the modulations in the photoelectron angular distributions.

Synopsis We present a non-perturbative semiclassical model for strong-field ionization that accounts for path interferences of tunnel-ionized electrons in the ionic potential within the framework of a classical trajectory Monte-Carlo representation of the phase-space dynamics.

The Photo Injector Test facility at DESY, Zeuthen site (PITZ), is dedicated to develop and optimize high brightness electron sources for short wavelength Free-Electron Lasers (FELs) like FLASH and the European XFEL, both in Hamburg (Germany). Since October 2009 a major upgrade is ongoing with the goal to improve the accelerating components, the photocathode drive laser system and the beam diagnostics as well. The essential new feature in the running will be an in-vacuum 10 MW RF directional coupler to be used for the RF monitoring and control. In this context a significant improvement of the RF stability is expected. RF pulses of 800 microseconds with 10 Hz repetition rate will be used. The most important upgrade of the diagnostics system will be the implementation of a phase space tomography module (PST) consisting of three FODO cells each surrounded by two screen stations. The goal is an improved measurement of the transverse phase space at different charge levels. The upgraded facility will be described.

ECG arrhythmias such as ventricular and atrial arrhythmias are one of the common causes of death. These abnormalities of the heart activity may cause an immediate death or cause a damage of the heart. In this paper, an arrhythmia classification algorithm is presented. The proposed method uses the nonlinear dynamical signal processing techniques to analyze the ECG signal in time domain. The classification algorithm is based upon the distribution of the attractor in the reconstructed phase space (RPS). The behavior of the ECG signal in the reconstructed phase space is used to determine the classification features of the whole classifier. To evaluate the performance of the presented classification algorithm, data sets are selected from the MIT database. Two groups of data, learning and testing datasets, are used to design and test the proposed algorithm. A classification sensitivity and specificity of 100% are used to fine tune the parameters of the selected features using the learning...

Classical nonlinear canonical (Poisson) maps have a distinguished role in quantum mechanics. They act unitarily on the quantum phase space and generateh-independent quantum canonical maps. It is shown that such maps act in the noncommutative phase space under the classical covariance. A crucial observation made is that under the classical covariance the local quantum mechanical picture can become nonlocal in the Hilbert space. This nonlocal picture is made equivalent by the Weyl map to a full noncommutative picture in the phase space formulation of the theory. The connection between the entanglement and nonlocality of the representation is explored and specific examples of the generation of entanglement by using the concept of generalized Bell states are provided. That the results have direct application in generating vacuum soliton configurations in the recently popular scalar field theories of noncommutative coordinates is also demonstrated.

In this communication we propose performing two-dimensional correlation operation between phase-space representations based on the fractional Fourier transform, instead of correlating the signals themselves. A numerical examples clearly indicates superior discrimination performance.

Synopsis We present a non-perturbative semiclassical model for strong-field ionization that accounts for path interferences of tunnel-ionized electrons in the ionic potential within the framework of a classical trajectory Monte-Carlo representation of the phase-space dynamics.

An extended quadrature method of moments using the beta kernel density function (beta-EQMOM) is used to approximate solutions to the evolution equation for univariate and bivariate composition probability distribution functions (PDFs) of a passive scalar for binary and ternary mixing. The key element of interest is the molecular mixing term, which is described using the Fokker-Planck (FP) molecular mixing model. The direct numerical simulations (DNSs) of Eswaran and Pope ["Direct numerical simulations of the turbulent mixing of a passive scalar,"Phys. Fluids 31, 506 (1988)] and the amplitude mapping closure (AMC) of Pope ["Mapping closures for turbulent mixing and reaction," Theor. Comput. Fluid Dyn. 2, 255 (1991)] are taken as reference solutions to establish the accuracy of the FP model in the case of binary mixing. The DNSs of Juneja and Pope ["A DNS study of turbulent mixing of two passive scalars,"Phys. Fluids 8, 2161 (1996)] are used to validate the results obtained for ternary mixing. Simulations are performed with both the conditional scalar dissipation rate (CSDR) proposed by Fox [Computational Methods for Turbulent Reacting Flows (Cambridge University Press, 2003)] and the CSDR from AMC, with the scalar dissipation rate provided as input and obtained from the DNS. Using scalar moments up to fourth order, the ability of the FP model to capture the evolution of the shape of the PDF, important in turbulent mixing problems, is demonstrated. Compared to the widely used assumed beta-PDF model [S. S. Girimaji, "Assumed beta-pdf model for turbulent mixing: Validation and extension to multiple scalar mixing," Combust. Sci. Technol. 78, 177 (1991)], the beta-EQMOM solution to the FP model more accurately describes the initial mixing process with a relatively small increase in computational cost.

In this communication we propose performing two-dimensional correlation operation between phase-space representations based on the fractional Fourier transform, instead of correlating the signals themselves. A numerical examples clearly indicates superior discrimination performance.

The Photo Injector Test facility at DESY, Zeuthen site (PITZ), is dedicated to develop and optimize high brightness electron sources for short wavelength Free-Electron Lasers (FELs) like FLASH and the European XFEL, both in Hamburg (Germany). Since October 2009 a major upgrade is ongoing with the goal to improve the accelerating components, the photocathode drive laser system and the beam diagnostics as well. The essential new feature in the running will be an in-vacuum 10 MW RF directional coupler to be used for the RF monitoring and control. In this context a significant improvement of the RF stability is expected. RF pulses of 800 microseconds with 10 Hz repetition rate will be used. The most important upgrade of the diagnostics system will be the implementation of a phase space tomography module (PST) consisting of three FODO cells each surrounded by two screen stations. The goal is an improved measurement of the transverse phase space at different charge levels. The upgraded facility will be described.

A novel and reliable approach which quantifies the degree of complexity of late potential (LP) activity in the time domain is presented. By defining the LP attractor in the microvoltage, 3-dimensional space, and then computing the fractal dimension (δ) of the attractor's trajectory, the degree of complexity of LP can be quantified with a single parameter. δ may indicate the

A quantum system Σ(n) with variables in Z(n), where n = Q pi (with pi prime numbers), is considered. The non-near-linear geometry G(n) of the phase space Z(n) × Z(n), is studied. The lines through the origin are factorized in terms of 'prime factor lines' in Z(pi)×Z(pi). Weak mutually unbiased bases (WMUB) which are products of the mutually unbiased bases in the 'prime factor Hilbert spaces' H(pi), are also considered. The factorization of both lines and WMUB is analogous to the factorization of integers in terms of prime numbers. The duality between lines and WMUB is discussed. It is shown that there is a partial order in the set of subgeometries of G(n), isomorphic to the partial order in the set of subsystems of Σ(n).

Quantum systems with finite Hilbert space where position x and momentum p take values in Z(d) (integers modulo d) are considered. Symplectic tranformations S(2ζ,Z(p)) in ζ-partite finite quantum systems are studied and constructed explicitly. Examples of applying such simple method is given for the case of bi-partite and tri-partite systems. The quantum correlations between the sub-systems after applying these transformations are discussed and quantified using various methods. An extended phase-space x−p−X−P where X, P ∈ Z(d) are position increment and momentum increment, is introduced. In this phase space the extended Wigner and Weyl functions are defined and their marginal properties are studied. The fourth order interference in the extended phase space is studied and verified using the extended Wigner function. It is seen that for both pure and mixed states the fourth order interference can be obtained. Ministry of Higher Education, Sultanate of Oman

We consider the concept of Stokes-Dirac structures in boundary control theory proposed by van der Schaft and Maschke. We introduce Poisson reduction in this context and show how Stokes-Dirac structures can be derived through symmetry reduction from a canonical Dirac structure on the unreduced phase space. In this way, we recover not only the standard structure matrix of Stokes-Dirac structures, but also the typical non-canonical advection terms in (for instance) the Euler equation.

The Photo Injector Test facility at DESY, Zeuthen site (PITZ), is dedicated to develop and optimize high brightness electron sources for short wavelength Free-Electron Lasers (FELs) like FLASH and the European XFEL, both in Hamburg (Germany). Since October 2009 a major upgrade is ongoing with the goal to improve the accelerating components, the photocathode drive laser system and the beam diagnostics as well. The essential new feature in the running will be an in-vacuum 10 MW RF directional coupler to be used for the RF monitoring and control. In this context a significant improvement of the RF stability is expected. RF pulses of 800 microseconds with 10 Hz repetition rate will be used. The most important upgrade of the diagnostics system will be the implementation of a phase space tomography module (PST) consisting of three FODO cells each surrounded by two screen stations. The goal is an improved measurement of the transverse phase space at different charge levels. The upgraded facility will be described.

Ultrafast electron diffractive imaging of nanoscale objects such as biological molecules 1,2 and defects in solid-state devices 3 provides crucial information on structure and dynamic processes: for example, determination of the form and function of membrane proteins, vital for many key goals in modern biological science, including rational drug design 4. High brightness and high coherence are required to achieve the necessary spatial and temporal resolution, but have been limited by the thermal nature of conventional electron sources and by divergence due to repulsive interactions between the electrons, known as the Coulomb explosion. It has been shown that, if the electrons are shaped into ellipsoidal bunches with uniform density 5 , the Coulomb explosion can be reversed using conventional optics, to deliver the maximum possible brightness at the target 6,7. Here we demonstrate arbitrary and real-time control of the shape of cold electron bunches extracted from laser-cooled atoms. The ability to dynamically shape the electron source itself and to observe this shape in the propagated electron bunch provides a remarkable experimental demonstration of the intrinsically high spatial coherence of a cold-atom electron source, and the potential for alleviation of electron-source brightness limitations due to Coulomb explosion 6. Carbon nanotube field emitters are at present the brightest available electron sources but must operate at low currents to avoid Coulomb expansion and are therefore not suitable for ultrafast imaging. Limited bunch shaping has been demonstrated with photoemission sources 7,8 , which use high-energy laser pulses to generate electrons at high current. Combined with longitudinal bunch compression, sub-100 fs pulses have been obtained with sufficient brightness for diffraction studies of gold 8,9. However, large increases in brightness are needed for single-shot imaging of weakly scattering materials such as biological molecules, and further increases in the brightness of intrinsically hot photoemission sources will be difficult. Recent simulations 10,11 and experiments 12 show that photoionization of a cold atom cloud can produce cold electron bunches with high coherence and current. Electrons are extracted by nearthreshold photoionization of atoms that have been laser-cooled to microKelvin temperature 13. We demonstrate here that the extracted electron bunches have extremely small transverse momentum, and show that the source has quasi-homogeneous rather than thermal coherence properties; that is, unlike conventional photocathode sources, the transverse locations of the cold electrons remain strongly correlated to their original location at the source. In addition, the internal structure of the atoms that form the underlying electron source provides a unique tool for three-dimensional control of the electron bunch shape 5. We show that it is possible to engineer the spatial profiles of the incident excitation and photoionization laser beams to control the shape

UltraCold Ion Beam Source. Focused ion beam (FIB) machines are largely used in the semiconductor industry mainly for imaging, milling and deposition of material, at the nanometer scale. To keep up with the trend of making smaller and smaller components, FIBs need to be continuously improved. A FIB is mainly made of an ion source and a focusing column. In this thesis, two concepts of ion sources are presented, modeled and discussed. The ultra-cold ion source (UCIS) is based on creating very cold ion beams (T <1 mK) by near-threshold photo-ionization of a laser-cooled and trapped atomic gas. In our experiment, 85Rb atoms are confined in a magneto optical trap built directly inside an accelerator structure. A spherical portion of the atom cloud is ionized with a 2-step ionization process and the bunched ions are accelerated by either a DC or a pulsed electric field. The liquid-metal ion source (LMIS) is the current state-of-art for focused ion beam technology, having a reduced brigh...

A new neural network system for classification of the cardiac rhythm is presented in this paper. The system is composed of two neural network classifiers : a morphological classifier cascaded to a timing classifier. While the morphological classifier classify the P and QRS complexes into normal and/or abnormal beats, the timing classifier takes as inputs the information of the morphological classifier and the duration of the PP, PR and RR intervals and output the following arrhythmias: sinus tachycardia, sinus bradycardia, sinus arrhythmia, atrial extrasystoles, atrial tachycardia, atrial fibrillation, atrial flutter, ventricular tachycardia, ventricular extrasystoles, ventricular flutter and supraventricular tachycardia in addition to the normal sinus rhythm.

A new neural network system for classification of the cardiac rhythm is presented in this paper. The system is composed of two neural network classifiers : a morphological classifier cascaded to a timing classifier. While the morphological classifier classify the P and QRS complexes into normal and/or abnormal beats, the timing classifier takes as inputs the information of the morphological classifier and the duration of the PP, PR and RR intervals and output the following arrhythmias: sinus tachycardia, sinus bradycardia, sinus arrhythmia, atrial extrasystoles, atrial tachycardia, atrial fibrillation, atrial flutter, ventricular tachycardia, ventricular extrasystoles, ventricular flutter and supraventricular tachycardia in addition to the normal sinus rhythm.

Photoionizing laser-cooled atoms produces ultracold neutral plasmas with initial temperatures of 1-1000 K and densities as high as 10 10 cm −3. Applied radio frequency fields can excite plasma oscillations that are used to monitor the expansion of the unconfined plasma. Significant three-body recombination of electrons and ions into Rydberg atoms takes place during the plasma expansion. Previous experiments have been done with xenon, but a new experiment is planned with laser-cooled strontium. The strontium ion has an optically allowed transition at a convenient blue wavelength. This will allow direct imaging of the plasma through fluorescence or absorption, and may enable laser cooling and trapping of the plasma.

Single shot diffraction imaging experiments via X-ray freeelectron lasers can generate as many as hundreds of thousands of diffraction patterns of scattering objects. Recovering the real space contrast of a scattering object from these patterns currently requires a reconstruction process with user guidance in a number of steps, introducing severe bottlenecks in data processing. We present a series of measures that replace user guidance with algorithms that reconstruct contrasts in an unsupervised fashion. We demonstrate the feasibility of automating the reconstruction process by generating hundreds of contrasts obtained from soot particle diffraction experiments.

We report a reconstruction of the phase space distribution of an X-ray beam after it has passed through a set of Young's slits. The resulting interference pattern has a quasi-probability distribution that has negative regions that do not have a classical interpretation. We experimentally reconstruct and observe these negative parts of the phase space distribution.

We present diffraction patterns from micron-sized areas of mono-crystalline graphite obtained with an ultracold and ultrafast electron source. We show that high spatial coherence is manifest in the visibility of the patterns even for picosecond bunches of appreciable charge, enabled by the extremely low source temperature (∼ 10 K). For a larger, ∼ 100 µm spot size on the sample, spatial coherence lengths > 10 nm result, sufficient to resolve diffraction patterns of complex protein crystals. This makes the source ideal for ultrafast electron diffraction of complex macromolecular structures such as membrane proteins, in a regime unattainable by conventional photocathode sources. By further reducing the source size, sub-µm spot sizes on the sample become possible with spatial coherence lengths exceeding 1 nm, enabling ultrafast nano-diffraction for material science.

Uniformly filled ellipsoidal (waterbag) electron bunches can be created in practice by space charge blow out of transversely tailored pancake bunches [1]. Ellipsoidal bunches have linear self fields in all dimensions, and will not deteriorate in quality under linear transport and acceler-ation. There is a discussion if such a bunch is better than a conventional beer-can shape. This paper compares the two approaches in terms of usable phase-space density. De-tailed GPT simulations of a simplified setup show that al-though the pancakes approach requires less charge, it is the application that is decisive.

We demonstrate compression of 95 keV, space-charge-dominated electron bunches to sub-100 fs durations. These bunches have sufficient charge (200 fC) and are of sufficient quality to capture a diffraction pattern with a single shot, which we demonstrate by a diffraction experiment on a polycrystalline gold foil. Compression is realized by means of velocity bunching as a result of a velocity chirp, induced by the oscillatory longitudinal electric field of a 3 GHz radio-frequency cavity. The arrival time jitter is measured to be 80 fs.

The influence has been studied of the ionization laser polarization on the effective temperature of an ultracold electron source, which is based on near-threshold photoionization. This source is capable of producing both high-intensity and high-coherence electron pulses, with applications in for example electron diffraction experiments. For both nanosecond and femtosecond photoionization, a sinusoidal dependence of the temperature on polarization angle has been found. For most experimental conditions, the temperature is minimal when the polarization coincides with the direction of acceleration. However, surprisingly, for nanosecond ionization a regime exists when the temperature is minimal when the polarization is perpendicular to the acceleration direction. This shows that in order to create electron bunches with the highest transverse coherence length, it is important to control the polarization of the ionization laser. The general trends and magnitudes of the temperature measurements are described by a model, based on the analysis of classical electron trajectories; this model further deepens our understanding of the internal mechanisms during the photoionization process. Furthermore, for nanosecond ionization, charge oscillations as a function of laser polarization have been observed; for most situations the oscillation amplitude is small. arXiv:1309.3417v2 [physics.atom-ph]

We present a method for producing sub-100 fs electron bunches that are suitable for single-shot ultrafast electron diffraction experiments in the 100 keV energy range. A combination of analytical results and state-of-the-art numerical simulations show that it is possible to create 100 keV, 0.1 pC, 20 fs electron bunches with a spotsize smaller than 500 µm and a transverse coherence length of 3 nm, using established technologies in a table-top set-up. The system operates in the space-charge dominated regime to produce energy-correlated bunches that are recompressed by established radio-frequency techniques. With this approach we overcome the Coulomb expansion of the bunch, providing an entirely new ultrafast electron diffraction source concept.

We report on a measurement of the characteristic temperature of an ultracold rubidium ion source, in which a cloud of laser-cooled atoms is converted to ions by photo-ionization. Extracted ion pulses are focused on a detector with a pulsed-field technique. The resulting experimental spot sizes are compared to particle-tracking simulations, from which a source temperature T = (1 ± 2) mK and the corresponding transversal reduced emittance ǫr = 7.9 × 10 −9 m rad √ eV are determined. We find that this result is likely limited by space charge forces even though the average number of ions per bunch is 0.022.

We report on a measurement of the characteristic temperature of an ultracold rubidium ion source, in which a cloud of laser-cooled atoms is converted to ions by photo-ionization. Extracted ion pulses are focused on a detector with a pulsed-field technique. The resulting experimental spot sizes are compared to particle-tracking simulations, from which a source temperature T = (1 ± 2) mK and the corresponding transversal reduced emittance ǫr = 7.9 × 10 −9 m rad √ eV are determined. We find that this result is likely limited by space charge forces even though the average number of ions per bunch is 0.022.

A normal-incident flattop laser with a tapered end is proposed as an optical undulator to achieve a high-gain and high-brightness X-ray free electron laser (FEL). The synchronic interaction of an electron bunch with the normal incident laser is realized by tilting the laser pulse front. The intensity of the flattop laser is kept constant during the interaction time of the electron bunch and the laser along the focal plane of a cylindrical lens. Optical shaping to generate the desired flattop pulse with a tapered end from an original Gaussian pulse distribution is designed and simulated. The flattop laser with a tapered end can enhance the X-ray FEL beyond the exponential growth saturation power by one order to reach 1 Gigawatt as compared to that without a tapered end. The peak brightness can reach 10 30 photons/mm 2 /mrad 2 /s/0.1% bandwidth, more than 10 orders brighter than the conventional incoherent Thompson Scattering X-ray source.

Two-photon ionization of Rubidium atoms in a magneto-optical trap and a Bose-Einstein condensate (BEC) is experimentally investigated. Using 100 ns laser pulses, we detect single ions photoionized from the condenstate with a 35(10)% efficiency. The measurements are performed using a quartz cell with external electrodes, allowing large optical access for BECs and optical lattices.

Ultracold atom-based electron sources have recently been proposed as an alternative to the conventional photo-injectors or thermionic electron guns widely used in modern particle accelerators. The advantages of ultracold atom-based electron sources lie in the fact that the electrons extracted from the plasma (created from near threshold photo-ionization of ultracold atoms) have a very low temperature, i.e. down to tens of Kelvin. Extraction of these electrons has the potential for producing very low emittance electron bunches. These features are crucial for the next generation of particle accelerators, including free electron lasers, plasmabased accelerators and future linear colliders. The source also has many potential direct applications, including ultrafast electron diffraction (UED) and electron microscopy, due to its intrinsically high coherence. In this paper, the basic mechanism of ultracold electron beam production is discussed and our new research facility for an ultracold, low emittance electron source is introduced. This source is based on a novel alternating current Magneto-Optical Trap (the AC-MOT). Detailed simulations for a proposed extraction system have shown that for a 1 pC bunch charge, a beam emittance of 0.35 mm mrad is obtainable, with a bunch length of 3 mm and energy spread 1 %.

We report a reconstruction of the phase space distribution of an X-ray beam after it has passed through a set of Young's slits. The resulting interference pattern has a quasi-probability distribution that has negative regions that do not have a classical interpretation. We experimentally reconstruct and observe these negative parts of the phase space distribution.

Single-particle experiments using X-ray Free Electron Lasers produce more than 10 5 snapshots per hour, consisting of an admixture of blank shots (no particle intercepted), and exposures of one or more particles. Experimental data sets also often contain unintentional contamination with different species. We present an unsupervised method able to sort experimental snapshots without recourse to templates, specific noise models, or user-directed learning. The results show 90% agreement with manual classification.

Changes in the normal rhythmicity of a human heart may result in
different cardiac arrhythmias, which may be immediately fatal or cause
irreparable damage to the heart when sustained over long periods of time. The
ability to automatically identify arrhythmias from ECG recordings is important
for clinical diagnosis and treatment, as well as, for understanding the
electrophysiological mechanisms of the arrhythmias. This paper proposes a
novel approach to efficiently and accurately identify normal sinus rhythm and
various ventricular arrhythmias through a combination of phase space
reconstruction and machine learning techniques. Data was recorded from
patients experiencing spontaneous arrhythmia, as well as, induced arrhythmia.
The phase space attractors of the different rhythms were learned from both
inter- and intra-patient arrhythmic episodes. Out-of-sample ECG rhythm
recordings were classified using the learned attractor probability distributions
with an overall accuracy of 83.0%