Near-threshold high-order harmonic spectroscopy with aligned molecules

We study high-order harmonic generation in aligned molecules close to the ionization threshold. Two distinct contributions to the harmonic signal are observed, which show very different responses to molecular alignment and ellipticity of the driving field. We perform a classical electron trajectory analysis, taking into account the significant influence of the Coulomb potential on the strong-field-driven electron dynamics. The two contributions are related to primary ionization and excitation processes, offering a deeper understanding of the origin of high harmonics near the ionization threshold. This work shows that high harmonic spectroscopy can be extended to the near-threshold spectral range, which is in general spectroscopically rich.Comment: 4 pages, 4 figure

CO2\mathrm{CO_2} exploding clusters dynamics probed by XUV fluorescence

Clusters excited by intense laser pulses are a unique source of warm dense matter, that has been the subject of intensive experimental studies. The majority of those investigations concerns atomic clusters, whereas the evolution of molecular clusters excited by intense laser pulses is less explored. In this work we trace the dynamics of $\mathrm{CO_2}$ clusters triggered by a few-cycle 1.45-$\mu$m driving pulse through the detection of XUV fluorescence induced by a delayed 800-nm ignition pulse. Striking differences among fluorescence dynamics from different ionic species are observed

Método Pilates e suas influências na autoestima : relato de experiência

O Método Pilates se propagou nas últimas décadas e, desde então, vem ganhando novos adeptos. É um programa de condicionamento físico e mental, realizado com aparelhos ou no solo, dentro de Academias ou Estúdios. Entre seus benefícios destacam-se força, alongamento, flexibilidade e equilíbrio, tendo o abdome como centro de força, exercícios realizados com poucas repetições. Sendo assim, como todo exercício físico regular, pode influenciar na autoestima de seus praticantes. Este relato tem como objetivo analisar a melhora na autoestima de praticantes de Pilates em um estúdio no Município de Porto Alegre-RS. Planejando atividades e uma metodologia nas aulas que possa contribuir para uma aula agradável e que mantenha o aluno interessado e disposto, influenciando na autoestima dos alunos, destacando que a prática regular de exercício físico pode contribuir para que as pessoas sintam- se bem, alegres, confiantes e saudáveis. Este estudo apresenta um relato da minha experiência na prática de instrutor de Pilates, durante o Estágio de Educação Física no Bacharelado, realizado no primeiro semestre de 2019, em um estúdio de Pilates com aproximadamente 50 alunos, elaborado através da análise do diagnóstico do Estúdio e das turmas, da observação das aulas, dos registros de meus diários e da avaliação da Autoestima dos alunos através de minha percepção. Este processo centralizado nas aulas de Pilates possibilitou aos alunos melhora nas capacidades físicas e mentais, melhorando seu controle corporal e reduzindo sua ansiedade, através disto melhorando sua autoestima e aprendendo a lidar com seu corpo, percebendo suas qualidades e capacidades físicas. Além disso, tivemos oportunidades de vivenciar o Método Pilates como um todo, de compartilhar as experiências, de buscar significados, de perceber o conteúdo presente nas aulas dentro do Estúdio e a importância das relações interpessoais e da progressão no desenvolvimento das atividades e suas influências na autoestima. Nas aulas, tivemos, a seguinte metodologia: parte inicial com aquecimento articular utilizando alongamentos nos aparelhos, logo uma parte mais aplicada a força e flexibilidade de membros inferiores e superiores, passando para uma parte mais avançada com desafios de equilíbrio e coordenação. Através de todas estas fases desenvolvemos uma produção de conhecimento e percepção corporal. No final do processo percebeu- se uma melhora na autoestima dos alunos.The Pilates Method has spread in recent decades and since then it has been gaining new adherents. It is a program of physical and mental conditioning, performed with appliances or on the ground, in gyms or studios. Among its benefits are strength, stretching, flexibility and balance, with the abdomen as the center of strength, exercises performed with few repetitions. Thus, like all regular exercise, it can influence the self-esteem of its practitioners. This report aims to analyze the improvement in Pilates practitioners' self-esteem in a studio in the city of Porto Alegre-RS. Planning activities and a methodology in the classes that can contribute to a pleasant class that keeps the student interested and willing, influencing students' self-esteem, emphasizing that regular physical exercise can contribute to make people feel good, happy, Confident and healthy. This study presents an account of my experience in Pilates instructor practice during the Bachelor Degree Physical Education Internship, held in the first semester of 2019, in a Pilates studio with approximately 50 students, prepared by analyzing the diagnosis of the Studio and of classes, observation of classes, journal entries, and assessment of students' Self-esteem through my perception. This process centered on Pilates classes allowed students to improve their physical and mental abilities, improve their body control and reduce their anxiety, thereby improving their self-esteem and learning how to deal with their body, realizing its qualities and physical abilities. In addition, we had opportunities to experience the Pilates Method as a whole, to share experiences, to search for meanings, to understand the content present in classes within the Studio and the importance of interpersonal relationships and progression in the development of activities and their influence on self esteem. In class, we had the following methodology: initial part with joint warming using stretching on the apparatus, then a part more applied to strength and flexibility of lower and upper limbs, moving to a more advanced part with challenges of balance and coordination. Through all these phases we develop a production of knowledge and body perception. At the end of the process, students' self- esteem improved

When does an electron exit a tunneling barrier?

We probe the dynamics of tunnel ionization via high harmonic generation. We characterize the ionization dynamics in helium atoms, and apply our approach to resolve subtle differences in ionization from different orbitals of a CO 2 molecule

Order-dependent structure of High Harmonic Wavefronts

The physics of high harmonics has led to the generation of attosecond pulses and to trains of attosecond pulses. Measurements that confirm the pulse duration are all performed in the far field. All pulse duration measurements tacitly assume that both the beam's wavefront and intensity profile are independent of frequency. However, if one or both are frequency dependent, then the retrieved pulse duration depends on the location where the measurement is made. We measure that each harmonic is very close to a Gaussian, but we also find that both the intensity profile and the beam wavefront depend significantly on the harmonic order. Thus, our findings mean that the pulse duration will depend on where the pulse is observed. Measurement of spectrally resolved wavefronts along with temporal characterization at one single point in the beam would enable complete space-time reconstruction of attosecond pulses. Future attosecond science experiments need not be restricted to spatially averaged observables

Rationale and design of the Apixaban for the Reduction of Thrombo-Embolism in Patients With Device-Detected Sub-Clinical Atrial Fibrillation (ARTESiA) trial.

BACKGROUND: Device-detected subclinical atrial fibrillation (AF) refers to infrequent, short-lasting, asymptomatic AF that is detected only with long-term continuous monitoring. Subclinical AF is common and associated with an increased risk of stroke; however, the risk of stroke with subclinical AF is lower than for clinical AF, and very few patients with subclinical AF alone have been included in large AF anticoagulation trials. The net benefit of anticoagulation in patients with subclinical AF is unknown. DESIGN: ARTESiA is a prospective, multicenter, double-blind, randomized controlled trial, recruiting patients with subclinical AF detected by an implanted pacemaker, defibrillator, or cardiac monitor, and who have additional risk factors for stroke. Patients with clinical AF documented by surface electrocardiogram will be excluded from the study. Participants will be randomized to receive either apixaban (according to standard AF dosing) or aspirin 81mg daily. The primary outcome is the composite of stroke, transient ischemic attack with diffusion-weighted magnetic resonance imaging evidence of cerebral infarction, and systemic embolism. Approximately 4,000 patients will be enrolled from around 230 clinical sites, with an anticipated mean follow-up of 36months until 248 adjudicated primary outcome events have occurred. SUMMARY: ARTESiA will determine whether oral anticoagulation therapy with apixaban compared with aspirin reduces the risk of stroke or systemic embolism in patients with subclinical AF and additional risk factors

High-order Harmonic Spectroscopy of the Cooper Minimum in Argon: Experimental and Theoretical Study

We study the Cooper minimum in high harmonic generation from argon atoms using long wavelength laser pulses. We find that the minimum in high harmonic spectra is systematically shifted with respect to total photoionization cross section measurements. We use a semi-classical theoretical approach based on Classical Trajectory Monte Carlo and Quantum Electron Scattering methods (CTMC-QUEST) to model the experiment. Our study reveals that the shift between photoionization and high harmonic emission is due to several effects: the directivity of the recombining electrons and emitted polarization, and the shape of the recolliding electron wavepacket.Comment: 13 page

Multi-channel electronic and vibrational dynamics in polyatomic resonant high-order harmonic generation

High-order harmonic generation in polyatomic molecules generally involves multiple channels of ionization. Their relative contribution can be strongly influenced by the presence of resonances, whose assignment remains a major challenge for high-harmonic spectroscopy. Here we present a multi-modal approach for the investigation of unaligned polyatomic molecules, using SF6 as an example. We combine methods from extreme-ultraviolet spectroscopy, above-threshold ionization and attosecond metrology. Fragment-resolved above-threshold ionization measurements reveal that strong-field ionization opens at least three channels. A shape resonance in one of them is found to dominate the signal in the 20-26 eV range. This resonance induces a phase jump in the harmonic emission, a switch in the polarization state and different dynamical responses to molecular vibrations. This study demonstrates a method for extending high-harmonic spectroscopy to polyatomic molecules, where complex attosecond dynamics are expected

Multidimensional high harmonic spectroscopy of polyatomic molecules: detecting sub-cycle laser-driven hole dynamics upon ionization in strong mid-IR laser fields

High harmonic generation (HHG) spectroscopy has opened up a new frontier in ultrafast science, where electronic dynamics can be measured on an attosecond time scale. The strong laser field that triggers the high harmonic response also opens multiple quantum pathways for multielectron dynamics in molecules, resulting in a complex process of multielectron rearrangement during ionization. Using combined experimental and theoretical approaches, we show how multi-dimensional HHG spectroscopy can be used to detect and follow electronic dynamics of core rearrangement on sub-laser cycle time scales. We detect the signatures of laser-driven hole dynamics upon ionization and reconstruct the relative phases and amplitudes for relevant ionization channels in a CO2 molecule on a sub-cycle time scale. Reconstruction of channel-resolved complex ionization amplitudes on attosecond time scales has been a long-standing goal of high harmonic spectroscopy. Our study brings us one step closer to fulfilling this initial promise and developing robust schemes for sub-femtosecond imaging of multielectron rearrangement in complex molecular systems