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Phase-matching analysis in high-order harmonic generation with nonzero orbital angular momentum Laguerre-Gaussian beams
Get PDFThrough high-order harmonic generation driven by intense ultrashort vortex infrared or midinfrared lasers, a nonzero orbital angular momentum can be imprinted onto extreme ultraviolet (XUV) or soft-x-ray (SXR) light pulses. Here we simulate the generation of vortex XUV harmonics in the gas medium as well as their propagation in vacuum till reaching the far field. We find that the intensity and phase of generated high harmonics are very sensitive to the position of gas jet with respect to the laser focus. The topological charge of the qth harmonic is found to be q times that of the driving Laguerre-Gaussian beam. Each harmonic in the far field appears as a single ring in the transverse plane with an invariant diameter which is scalable with the fundamental topological charge only when the gas jet is placed after the laser focus. The underlying phase-matching mechanism is analyzed by examining the spatial map of the coherence length and by calculating the evolution of harmonic emission in the medium. We anticipate this work to stimulate interest in generating intense vortex XUV or SXR attosecond pulses for probing dynamics of molecules where special molecular features are difficult to be detected with linear or circular XUV or SXR pulses
Two-color-driven enhanced high-order harmonic generation in solids
Get PDFWe theoretically investigate the emission of high-harmonic (HH) radiation in model crystals by bichromatic few-cycle driving pulses that are composed as the phase-coherent superposition of a mid-infrared fundamental pulse and its second harmonic. Adjusting the model-crystal parameters to reproduce the lowest band gap of MgO, we examine the extent to which distinct domains of the HH spectrum can be controlled and enhanced by tuning the temporal profile of the bichromatic driving laser electric field. We change the driving-pulse shape by varying its fundamental-versus-second-harmonic pulse amplitude ratio and delay, while keeping the energy of the driving laser pulse fixed. For suitable amplitude ratios and delays, we find an up to fivefold enhancement of the spectral HH yield and significant shifts of the HH cutoff frequency
Vibrant Communitites with a Postive Future Kansas PRIDE Impact 2019 - 2020
No full textSummary of the 2019-2020 actiivities of the Kansas PRIDE program and affiliated communities
Mapping Resonance Structures in Transient Core-Ionized Atoms
Get PDFThe nature of transient electronic states created by photoabsorption critically determines the dynamics of the subsequently evolving system. Here, we investigate K-shell photoionized atomic neon by absorbing a second photon within the Auger-decay lifetime of 2.4 fs using the European XFEL, a unique high-repetition-rate, wavelength-tunable x-ray free-electron laser. By high-resolution electron spectroscopy, we map out the transient Rydberg resonances unraveling the details of the subsequent decay of the hollow atom. So far, ultra-short-lived electronic transients, which are often inaccessible by experiments, were mainly inferred from theory but are now addressed by nonlinear x-ray absorption. The successful characterization of these resonances with femtosecond lifetimes provides the basis for a novel class of site-specific, nonlinear, and time-resolved studies with strong impact for a wide range of topics in physics and chemistry
Separability of H2O molecular potential surfaces in hyperspherical coordinates via adiabatic approximation
Get PDFAn adiabatic scheme for separation of the three-dimensional (3D) nuclear dynamics on the ground electronic Born-Oppenheimer potential energy surface of an H2O molecule in hyperspherical coordinates is presented. It is found that the three vibrational modes are weakly coupled and the 3D vibrational wave function can be approximated as a product of three separable functions: one represented by the hyperradius and two by the two hyperangles individually. This framework is then used for investigation of the formation and the role of a saddlelike barrier arising in the two hyperspherical angles that is to moderate the OH + H dissociation process. In order to test the validity of the framework, vibrational states with energies up to 19 500 cm−1 are constructed under the assumptions of adiabaticity and separability and compared to full three-dimensional high-precision numerical calculations yielding remarkable correspondence. As a result we present a simple construction scheme for separated molecular vibration states as the first step towards theoretical investigation of laser-driven molecular dynamics of triatomic molecules
Time-resolved site-selective imaging of predissociation and charge transfer dynamics: the CH3I B-band
Get PDFThe predissociation dynamics of the 6s (B2E) Rydberg state of gas-phase CH3I were investigated by time-resolved Coulomb-explosion imaging using extreme ultraviolet (XUV) free-electron laser pulses. Inner-shell ionization at the iodine 4d edge was utilized to provide a site-specific probe of the ensuing dynamics. The combination of a velocity-map imaging (VMI) spectrometer coupled with the pixel imaging mass spectrometry (PImMS) camera permitted three-dimensional ionic fragment momenta to be recorded simultaneously for a wide range of iodine charge states. In accord with previous studies, initial excitation at 201.2 nm results in internal conversion and subsequent dissociation on the lower-lying A-state surface on a picosecond time scale. Examination of the time-dependent yield of low kinetic energy iodine fragments yields mechanistic insights into the predissociation and subsequent charge transfer following multiple ionization of the iodine products. The effect of charge transfer was observed through differing delay-dependencies of the various iodine charge states, from which critical internuclear distances for charge transfer could be inferred and compared to a classical over-the-barrier model. Time-dependent photofragment angular anisotropy parameters were extracted from the central slice of the Newton sphere, without Abel inversion, and highlight the effect of rotation of the parent molecule before dissociation, as observed in previous works. Our results demonstrate the ability to perform three-dimensional ion imaging at high event rates and showcase the potential benefits of this approach, particularly in relation to further time-resolved studies at free-electron laser facilities
A Model for Improving Diet Quality within Child Nutrition Programs: The U.S. Army’s Child and Youth Services Healthy Menu Initiative
Get PDFThe U.S. Army’s Child, Youth, and School Services (CYS), which has the capacity to serve more than 70,000 meals/snacks per day, is a geographically dispersed system with facilities worldwide. This case report is a description and evaluation of the implementation of a major food program initiative within the CYS system. In collaboration with Kansas State University, the Healthy Menu Initiative was established to standardize the system’s menus, reflect the guidance contained within the 2015–2020 Dietary Guidelines for Americans, and take into account the Child and Adult Care Food Program regulations that went into effect on 1 October 2017. Food storage space, food service equipment, product availability, food safety considerations, and staff shortages have all proven to be challenges in the development and implementation of the menus. Participant acceptance has been an issue in some instances, and special diet requirements add to the workload of the staff. To overcome these challenges, input was solicited from CYS management, care providers, food service staff, and participant families, as well as participants themselves. Taste testing and classroom cooking activities have been developed to increase acceptance, and over 500 CYS food program staff have attended in-depth training sessions to support the initiative. Overall, the initiative has been well received, and there has been an improvement in the diet quality of the foods served within the program. This improvement is noteworthy, as optimal growth and development during childhood and adolescence are reliant on sound nutrition
Report of Progress 1156
Get PDFSunflower performance tests were conducted by the Kansas Agricultural Experiment Station to provide farmers, extension workers, and private industry with unbiased agronomic information on many of the sunflower hybrids marketed in the state. Environmental factors affecting test results and cultural practices are presented for each individual test site
2019 Kansas Performance Tests with Grain Sorghum Hybrids
No full textGrain Sorghum Performance Tests, conducted annually by the Kansas Agricultural Experiment Station, provide farmers, extension workers, and seed industry personnel with unbiased agronomic information on many of the grain sorghum hybrids marketed in the state. Because entry selection and location are voluntary, not all hybrids grown in the state are included in tests, and the same group of hybrids is not grown at all test locations
Level Up! Making Games Accessible
Get PDFGames are firmly established as a tool in the librarian’s toolbox. Gamification of instruction allows librarians to reach more students in instruction both online and in person by creating more engaging library instruction sessions or online tutorials. Library game nights and other programming that includes games allow us to draw more students into the library. Unfortunately, instructional and outreach activities that are not designed with accessibility and inclusivity in mind from the beginning can make students with disabilities feel unwelcome in the library. In this chapter, we will cover some of the foundational aspects of accessible gamification. We will also detail how to prepare for potential accessibility pitfalls and suggest possible remedies