Arbitrarily shaped high-coherence electron and ion bunches from laser-cooled atoms

Thermal emission from blackbody is typically incoherent and broadband. Achieving highly coherent thermal source while eliminating the rainbow effect has been remaining a challenging task. In our study, we utilize the isolated nature of bound states in the continuum (BICs) at the Γ point to achieve thermal emission with high temporal and spatial coherence. Under the framework of temporal coupled mode theory (TCMT), we can significantly reduce the Q-factors of modes outside the Γ point by employing far-field coupling of modes in different polarization channels within momentum space, thereby suppressing the rainbow effect. Our design, experimentally validated through ternary grating structures, demonstrates thermal emission centered at 6.5 μm with a 23 nm bandwidth, confined within a 2° angular range. This advancement holds significant implications for the miniaturization and integration of thermal radiation devices, with potential applications in infrared imaging, sensing, and energy harvesting.

The accidental Dirac cone of a photonic crystal allows the realization of a low loss dielectric metamaterial with simultaneous near-zero effective permittivity and permeability. The resulting zero refractive index allowed applications that require unique spatial coherency. While most thermal light sources were considered highly incoherent, structurally engineered thermal emitters have achieved relatively high spatial coherency. Here, we propose an epsilon-and-mu-near-zero metamaterial as a spatial coherency converter for thermal emissions, and experimentally demonstrate surface-normal directional emissions with an angular width of 20 degrees.

We report speckle-free digital holographic phase microscopy (DHPM) and tomography using partially spatially coherent monochromatic light with improved image sharpness, resolution and phase noise. Effects of high spatial and temporal coherence of laser light in DHPM, such as speckle effect, spurious fringe generation are discussed and these effects lead to poor phase reconstruction. We present our recent work on the speckle-free phase microscopy and spatial coherence gated tomography with improved phase reconstruction and resolution.

We implement high-efficiency coherent excitation to a Rydberg state using stimulated Raman adiabatic passage in a cold atom electron and ion source. We achieve an efficiency of 60% averaged over the laser excitation volume with a peak efficiency of 82%, a 1.6 times improvement relative to incoherent pulsed-laser excitation. Using pulsed electric field ionization of the Rydberg atoms we create electron bunches with durations of 250 ps. High-efficiency excitation will increase source brightness, crucial for ultrafast electron diffraction experiments, and coherent excitation to high-lying Rydberg states could allow for the reduction of internal bunch heating and the creation of a high-speed single ion source.

Event Abstract Back to Event Effects of nonlocal coupling on the dynamics of neural systems Philipp Hövel1, 2* and Iryna Omelchenko1, 2 1 Technische Universität Berlin, Physics, Germany 2 Bernstein Center for Computational Neuroscience Berlin, Germany Understanding the dynamics on networks is at the heart of modern nonlinear science and has a wide applicability to neuroscience. The interplay of network topology and local dynamics opens a variety of dynamical phenomena such as synchronization, clustering, waves, kinks, complex patterns, and chaos. Here we study the spatio-temporal dynamics of coupled neural oscillators with nonlocal interactions. In the considered configuration each element is coupled to its nearest neighbors within a finite range. Depending upon the control parameters chosen as coupling strength and coupling radius, we investigate the cooperative dynamics in a generic model for type-II excitability given by FitzHugh-Nagumo equations. The individual systems are considered to operate above a Hopf bifurcation, that is, they operate in the oscillatory regime. On the basis of previous results on nonlocally coupled discrete maps and chaotic systems, we demonstrate the universality of a transition from coherence to incoherence in such systems, giving rise to spatial chaos and so-called chimera states. The latter arise as hybrid spatial patterns in regular networks of identical oscillators and consist of parts with high spatial coherence and regions where spatial coherence is lost. We analyze the regions of stability of various types of solutions in the parameter space of coupling strength and coupling radius: completely synchronous oscillations, wave-like profiles, cluster states as well as partially incoherent states. Furthermore, we study the robustness of the observed patterns in the presence of inhomogeneities of the local elements that are introduced via different threshold parameters in the FitzHugh-Nagumo system. Acknowledgements Supported by the BMBF under the grant no. 01GQ1001B (Förderkennzeichen). Keywords: dynamics, incoherence, nonlocal coupling, oscillations, synchronization Conference: Bernstein Conference 2012, Munich, Germany, 12 Sep - 14 Sep, 2012. Presentation Type: Poster Topic: Abstracts Citation: Hövel P and Omelchenko I (2012). Effects of nonlocal coupling on the dynamics of neural systems. Front. Comput. Neurosci. Conference Abstract: Bernstein Conference 2012. doi: 10.3389/conf.fncom.2012.55.00221 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 10 May 2012; Published Online: 12 Sep 2012. * Correspondence: Dr. Philipp Hövel, Technische Universität Berlin, Physics, Berlin, 10623, Germany, phoevel@physik.tu-berlin.de Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Philipp Hövel Iryna Omelchenko Google Philipp Hövel Iryna Omelchenko Google Scholar Philipp Hövel Iryna Omelchenko PubMed Philipp Hövel Iryna Omelchenko Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

We have coherently combined a high-power broad-area laser diode array by using a feedback loop closed off-axis external Talbot cavity. The off-axis feedback from two gratings provides transverse-mode control of broad-area lasers. The Talbot configuration of the external cavity implements diffractive coupling among laser diodes. Feedback from two gratings increases external cavity quality factor and spectrum selection capability. As a result, spatial coherence was improved and spectral linewidth was narrowed down. The high visibility of the far-field profile indicates that high spatial coherence was achieved. We also observed symmetric far-field profiles indicating that laser array was phase locked to in-phase and out-of-phase super-modes, respectively. Transition between these super-modes was observed by tuning one grating's tilted angle.

An experomental study of stimulated Raman conversion of high-coherent XeCl laser radiation in H2 has been carried out. About 50 vibrational-rotational components were realized with a circularly polarized laser beam pump. High spatial and temporal coherence of conversed radiation was obtained. Quantum efficiency of conversion in first vibrational Stokes was achieved 95%.

To predict the coherence in local responses to large-scale climatic forcing among aquatic systems, we developed a generalized approach to compare long-term data of dimictic water bodies based on phenomenologically defined hydrographic events. These climate-sensitive phases (inverse stratification, spring overturn, early thermal stratification, summer stagnation) were classified in a dual code (cold/warm) based on threshold temperatures. Accounting for a latitudinal gradient in seasonal timing of phases derived from gradients in cumulative irradiation (2.2 days per degree latitude), we found a high spatial and temporal coherence in warm–cold patterns for six lakes (84 %) and the Baltic Sea (78 %), even when using the same thresholds for all sites. Similarity to CW-codes for the North Sea still was up to 72 %. The approach allows prediction of phase-specific warming trends and resulting instantaneous or time-delayed ecological responses. Exemplarily, we show that warming during early thermal stratification controls food-web-mediated effects on key species during summer.

Ultrafast electron diffraction enables the study of molecular structural dynamics with atomic resolution at subpicosecond timescales, with applications in solid-state physics and rational drug design. Progress with ultrafast electron diffraction has been constrained by the limited transverse coherence of high-current electron sources. Photoionization of laser-cooled atoms can produce electrons of intrinsically high coherence, but has been too slow for ultrafast electron diffraction. Ionization with femtosecond lasers should in principle reduce the electron pulse duration, but the high bandwidth inherent to short laser pulses is expected to destroy the transverse coherence. Here we demonstrate that a two-colour process with femtosecond excitation followed by nanosecond photoionization can produce picosecond electron bunches with high transverse coherence. Ultimately, the unique combination of ultrafast ionization, high coherence and three-dimensional bunch shaping capabilities of cold atom electron sources have the potential for realising the brightness and coherence requirements for single-shot electron diffraction from crystalline biological samples.

A novel way of creating low-temperature electron and ion beams is demonstrated. The beams are generated by converting a laser-cooled atom cloud to a highly excited Rydberg gas, which subsequently develops into an ultracold plasma. Charged particles are extracted from the Rydberg gas and the plasma by a pulsed electric field. The properties of the resulting electron and ion pulses are experimentally studied. Pulses of a few hundred ns duration containing a few pC of charge were observed. Upper limits for the temperature of such beams (60K for ions and 500K for electrons) are obtained, and the beams are shown to have low emittance. Further development of the method may lead to the generation of high-brightness charged-particle beams from ultracold plasmas.

An analytical formula is derived for the dependence of the statistical properties of speckle pattern on the roughness phase correlation coefficient and roughness variance. Gaussian phase probability density distributions of zero and non-zero phase mean value are assumed for the surface roughness. Radiation of high temporal and spatial coherence is used for illuminating the surfaces of different roughness. The optical roughness of the object is controlled by changing the refractive index of the medium in front of it at constant temperature. The theoretical results indicate a similarity of the derived statistical properties of the speckle pattern for both considered cases of the Gaussian phase probability density distributions. An experiment is carried out to validate the obtained theoretical formula. The experimental measurements show good agreement with the theoretical derived formula. The theoretical development and the experimental work allowed the roughness phase correlation coefficient to be determined.

A program devoted to perform the first in-vivo monochromatic breast computed tomography (BCT) is ongoing at the Elettra Synchrotron Facility. Since the synchrotron radiation provides high energy resolution and spatial coherence, phase-contrast (PhC) imaging techniques can be used. The latest high resolution BCT acquisitions of breast specimens, obtained with the propagation-based PhC approach, are herein presented as part of a wider framework, devoted to the optimization of acquisition and reconstruction parameters towards the clinical exam. Images are acquired with a state-of-the-art dead-time-free single-photon-counting CdTe detector with a 60 µm pixel size. The samples are imaged at 32 and 38 keV in continuous rotating mode, delivering 5-20 mGy of mean glandular dose (MGD). Contrast-to-noise ratio (CNR) and spatial resolution performances are evaluated for both absorption and phase-retrieved images considering tumor/adipose tissue interfaces. We discuss two different phase-retrieval approaches, showing that a remarkable CNR increase (from 0.5 to 3.6) can be obtained without a significant loss in spatial resolution. It is shown that, even if the non-phase-retrieved image has a poorer CNR, it is useful for evaluating the spiculation of a microcalcification: in this context, absorption and phase-retrieved images have to be regarded as complementary information. Furthermore, the first full volume acquisition of a mastectomy, with a 9 cm diameter and 3 cm height, is reported. This investigation on surgical specimens indicates that monochromatic BCT with synchrotron radiation in terms of CNR, spatial resolution, scan duration and scan volume is feasible.

New light sources with low spatial coherence and high brightness are crucial for high‐quality imaging. In this paper, such a light source is reported, which is formed by combining random lasing used as seed light with a multimode fiber (MMF) mediated master oscillator power amplifier (MOPA) for power scaling and spatial decoherence. Experimental results show that the proposed multimode random fiber laser (MM‐RFL), with low noise, high spectral density, and high power efficiency, can achieve a maximum output power of 100.6 W and speckle contrast of as low as 0.037. Furthermore, MM‐RFL‐based speckle‐free imaging is demonstrated. The imaging quality can be improved by increasing the output power of the MM‐RFL as its spatial coherence decreases with an increasing number of effective modes excited in the MMF. Such a MM‐RFL provides a powerful light source for speckle‐free imaging applications where high power and low spatial coherence are essential for high‐quality imaging.

ArF-dry microlithography is currently switching from pre-production to mass-production and the target node is shifted from 90 nm to 65 nm. ArF-wet or F₂ laser lithography will then be an important player for the next generation node below 45 nm. Therefore, high throughput and high-resolution exposure tools for VUV lithography require VUV light sources (ArF and F₂ lasers) with high power and narrow bandwidth. In this paper, we describe the beam quality of the new- type injection lock (MOPO, master oscillator power oscillator) ArF laser system we developed and compare it with the beam quality of a master oscillator power amplifier (MOPA) ArF laser system. A high power and narrow bandwidth ArF laser can be achieved with twin laser chambers in a MOPA or an injection lock laser configuration. Compared to the MOPA system, the injection lock laser system has an excellent performance (e.g. high efficiency, long pulse duration and narrow spectrum). On the other hand, the injection lock system has some disadvantages in beam quality showing high spatial coherence, broadband emission and having a beam profile with a hole. These technical issues have been solved, however, with the following two new breakthrough-technologies: (1) a new-type injection lock system having low spatial coherence and a beam profile with no hole and (2) the optimization of the injection seed energy and discharge timing between the twin chambers for low broadband emission. The spatial coherence, the broadband spectrum and the beam profile of the new-type injection lock system were measured with a Young's interferometer, a wide range spectrometer with etalons and a 2-dimensional beam profiler, respectively. The new-type injection lock ArF laser system had a lower spatial coherence than a conventional injection lock system, a very low broadband emission level thus preventing deterioration of exposure tools resolution, and a beam profile with no hole. Moreover, we reconfirmed that the new-type injection lock system has the same excellent performance as the conventional injection lock system.

Sub-4-fs high harmonic pulses with photon energy of 27.9 eV were generated by using the 20-fs second harmonic pulses of Ti:sapphire laser, produced by the broadband- frequency conversion. The 27.9-eV pulses were fully characterized by the cross-correlation frequency resolved optical gating technique. A nonlinear optical process in the extreme ultraviolet (XUV) region, i.e. above-threshold ionization of helium atoms, by the high harmonic pulses was observed, demonstrating the high harmonic generation with high spatial and temporal coherence. This enables the autocorrelation measurement of attosecond pulses.KeywordsHelium AtomExtreme UltravioletSecond HarmonicShort Pulse DurationHigh Harmonic GenerationThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.