A5027388617- Laser-Matter Interactions and Applications
- Atomic and Molecular Physics
- Mass Spectrometry Techniques and Applications
- Laser-induced spectroscopy and plasma
- Laser Design and Applications
- Advanced Chemical Physics Studies
- Laser-Plasma Interactions and Diagnostics
- Ion-surface interactions and analysis
- Spectroscopy and Quantum Chemical Studies
- Advanced Fiber Laser Technologies
- Atomic and Subatomic Physics Research
- Spectroscopy and Laser Applications
- Nuclear Physics and Applications
- Nuclear physics research studies
- Astro and Planetary Science
- Quantum, superfluid, helium dynamics
- Cold Atom Physics and Bose-Einstein Condensates
- X-ray Spectroscopy and Fluorescence Analysis
- Quantum optics and atomic interactions
- Particle Accelerators and Free-Electron Lasers
- Particle accelerators and beam dynamics
- Quantum Chromodynamics and Particle Interactions
- Astrophysics and Star Formation Studies
- Gamma-ray bursts and supernovae
- High-Energy Particle Collisions Research
Kansas State University
2015-2024
Augustana University
2020
Colorado State University
2012
East Carolina University
2009
Purdue University West Lafayette
1986-1988
Roaming mechanisms, involving the brief generation of a neutral atom or molecule that stays in vicinity before reacting with remaining atoms precursor, are providing valuable insights into previously unexplained chemical reactions. Here, mechanistic details and femtosecond time-resolved dynamics H3+ formation from series alcohols varying primary carbon chain lengths obtained through combination strong-field laser excitation studies ab initio molecular calculations. For small alcohols, four...
Abstract Strong-field laser-matter interactions often lead to exotic chemical reactions. Trihydrogen cation formation from organic molecules is one such case that requires multiple bonds break and form. We present evidence for the existence of two different reaction pathways H 3 + irradiated by a strong-field laser. Assignment was accomplished through analysis femtosecond time-resolved ionization photoion-photoion coincidence measurements carried out on methanol isotopomers, ethylene glycol,...
A key question concerning the three-body fragmentation of polyatomic molecules is distinction sequential and concerted mechanisms, i.e., stepwise or simultaneous cleavage bonds. Using laser-driven OCS into O^{+}+C^{+}+S^{+} employing coincidence momentum imaging, we demonstrate a novel method that enables clear separation breakup. The accomplished by analyzing in native frame associated with each step taking advantage rotation intermediate molecular fragment, CO^{2+} CS^{2+}, before its...
Abstract An essential problem in photochemistry is understanding the coupling of electronic and nuclear dynamics molecules, which manifests processes such as hydrogen migration. Measurements migration molecules that have more than two equivalent sites, however, produce data difficult to compare with calculations because initial site unknown. We demonstrate coincidence ion-imaging measurements a few deuterium-tagged isotopologues ethanol can determine contribution each initial-site...
Laser-induced dissociation and ionization of $\mathrm{H}_{2}{}^{+}$ were simultaneously measured using coincidence 3D momentum imaging, allowing direct separation the two processes, even where fragment kinetic energy is same for both processes. The results 45 135 fs 790 nm pulses with an intensity approximately $2.5\ifmmode\times\else\texttimes\fi{}{10}^{14}\text{ }\text{ }\mathrm{W}/{\mathrm{cm}}^{2}$ differ from each other much more than one would expect previous measurements longer...
We have measured and explained a new mechanism of molecular ionization near the appearance intensity that produces sequence peaks in nuclear kinetic energy spectrum separated by photon energy. Our interpretation is based on an internally consistent model for motion during intense laser pulse. Within this model, same concepts language can be used both dissociation ionization, leading to more unified understanding dynamics.
The dissociation of $\mathrm{H}_{2}{}^{+}$ in an intense laser field has been experimentally studied using femtosecond pulses at $790\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ the intensity range ${10}^{13}--{10}^{15}\phantom{\rule{0.3em}{0ex}}\mathrm{W}∕{\mathrm{cm}}^{2}$. Kinematically complete measurements both ionic ${\mathrm{H}}^{+}$ and neutral H fragments dissociated from a vibrationally excited beam have achieved by coincidence three-dimensional momentum imaging system. Angular-resolved...
High-order (three-photon or more) above-threshold dissociation (ATD) of ${\mathrm{H}}_{2}^{+}$ has generally not been observed using 800 nm light. We demonstrate a strong enhancement its probability intense 7 fs laser pulses interacting with beams ${\mathrm{H}}_{2}^{+}$, ${\mathrm{HD}}^{+}$, and ${\mathrm{D}}_{2}^{+}$ ions. The mechanism invokes dynamic control the pathway. These measurements are supported by theory that additionally reveals, for first time, an unexpectedly large...
The dissociation of an H$_2^+$ molecular-ion beam by linearly polarized, carrier-envelope-phase-tagged 5 fs pulses at 4$\times10^{14} $W/cm$^2$ with a central wavelength 730 nm was studied using coincidence 3D momentum imaging technique. Carrier-envelope-phase-dependent asymmetries in the emission direction H$^+$ fragments relative to laser polarization were observed. These are caused interference odd and even photon number pathways, where net-zero 1-photon predominantly contributes H$^+$+H...
In a joint experimental and theoretical endeavor, we explore the laser-induced dissociation ionization dynamics of H${{}_{2}}^{\phantom{\rule{-0.16em}{0ex}}\phantom{\rule{-0.16em}{0ex}}+}$ beams using sub-10-fs, 800 nm laser pulses. Our theory predicts considerable control over branching ratio two-photon three-photon above-threshold (ATD) by gating pathway on few-femtosecond timescale. We are able to experimentally demonstrate this control. Moreover, our also shows importance highly excited...
Domestic and nondomestic cats have been shown to be susceptible feline spongiform encephalopathy (FSE), almost certainly caused by consumption of bovine (BSE)-contaminated meat. Because domestic free-ranging felids scavenge cervid carcasses, including those in areas affected chronic wasting disease (CWD), we evaluated the susceptibility cat (Felis catus) CWD infection experimentally. Cohorts 5 each were inoculated intracerebrally (i.c.) or orally (p.o.) with CWD-infected deer brain. At 40 42...
In a recent Letter, Manschwetus et al. [Phys. Rev. Lett. 102, 113002 (2009)] reported evidence of electron recapture during strong-field fragmentation H${}_{2}$---explained using frustrated tunneling ionization model. Unusually, the signature this process was detection excited H${}^{*}$ atoms. We report here an extensive study in D${}_{2}$. Our measurements encompass pulse duration, intensity, ellipticity, and angular distribution dependence D${}^{*}$ formation. While we find that mechanism...
Multiple-electron removal from and molecular fragmentation of carbon monoxide molecules caused by collisions with 1-MeV/amu ${\mathrm{F}}^{4+}$ ions were studied using the coincidence time-of-flight technique. In these collisions, multiple-electron target molecule is a dominant process. Cross sections for different levels ionization CO during collision determined. The relative cross decrease increasing number electrons removed in similar way as seen atomic targets. This behavior agreement...
An intensity-difference spectrum method is developed to disentangle the intensity volume effect inherent in focused laser beam interaction with gas-phase matter. This applicable a Gaussian of constant axial intensity, which keeps exact contribution from predetermined range and eliminates contributions lower intensities. We apply this angularly resolved kinetic energy release laser-induced dissociation H2+. The difference at higher intensities found be dominated by bond-softening process,...
A method for determining the laser-induced dissociation pathways of multielectron diatomic molecules is developed. Despite abundance possible inherent to such molecules, this technique allows one resolve that contribute measured intensity-dependent three-dimensional momentum distribution. To illustrate method, unique mechanisms and producing a few predominant features in distribution ${\mathrm{O}}_{2}^{+}$ are determined.
The $\mathrm{H}_{3}{}^{+}$ ion is the simplest polyatomic molecule and destined to play a central role in understanding such molecules intense ultrashort laser pulses. We present first measurements of field dissociation ionization $\mathrm{D}_{3}{}^{+}$ using coincidence three-dimensional momentum imaging. Our results show features that are consequence this molecule's unique equilateral triangular geometry, providing fundamentally new system for theoretical development.
We reveal surprisingly high kinetic energy release in the intense-field fragmentation of D3+ to D+ + D with 1016 W cm−2, 790 nm, 40 fs (and 7 fs) laser pulses. This feature strongly mimics behaviour channel. From experimental evidence, we conclude that origin is due frustrated tunnelling ionization, first observation this mechanism a polyatomic system. Furthermore, unravel evidence ionization dissociation, both two-body breakup D2+ and D2, three-body D.
A comparative study of bond rearrangement is reported for the double ionization three triatomic molecules: carbon dioxide, carbonyl sulfide, and water (${\mathrm{D}}_{2}\mathrm{O}$). Specifically, we formation molecular cation ${\mathrm{AC}}^{+}$ from edge atoms a dication ${\mathrm{ABC}}^{2+}$ following by intense, short (23 fs, 790 nm) laser pulses. The comparison made using branching ratio each molecule, thereby minimizing differences due to differing rates. highest water, which has bent...
The Coulomb explosion of tribromomethane (bromoform, CHBr3) induced by 28 fs near-infrared laser pulses is investigated three-dimensional coincidence ion momentum imaging. We focus on the fragmentation into three, four, and five ionic fragments measured in present different ways visualizing correlations. show that experimentally observed correlations for 4- 5-fold coincidences are well reproduced classical simulations contain information about structure parent molecule could be used to...
Enhanced ionization of $\mathrm{H}_{2}{}^{+}$ in intense ultrashort laser pulses was measured using molecular dissociation imaging an beam and with a pump-probe technique cold target recoil ion momentum spectroscopy on ${\mathrm{D}}_{2}$ target. Both measurements show broad, single-peak distribution for enhanced ionization, contrast to the double-peak structure predicted by ``frozen'' nuclei theory. This calculated is most likely washed out nuclear motion lesser extent intensity averaging.
We studied the fragmentation of planar formic acid (HCOOH) molecules following their double ionization by intense ultrashort laser pulses. Deuterium tagging (i.e., HCOOD) combined with coincidence momentum imaging measurements all fragment ions enabled determination role hydroxyl and carboxyl hydrogen atoms in breakup. Specifically, we observe a strong preference for (OD) group to remain intact...
The cross sections of the different breakup channels ${\mathrm{CH}}_{4}$, produced by 4-MeV proton impact, have been measured using coincidence time-of-flight technique. relative abundances were evaluated for collisions in which molecule broke into two charged fragments as well where only a single molecular ion or fragment was produced. These are compared to ones photodissociation, and electron impact. Only ${\mathrm{CH}}_{4}^{+}$ survives long enough be detected ion, while doubly...
We demonstrate a chirped-pulse-amplified Ti:Sapphire laser system operating at 1 kHz, with 20 mJ pulse energy, 26 femtosecond duration (0.77 terawatt), and excellent long term carrier-envelope-phase (CEP) stability. A new vibrational damping technique is implemented to significantly reduce noise on both the stretcher compressor, thus enabling single-shot CEP value of 250 mrad RMS over hour 300 9 hours. This is, best our knowledge, ever reported for any terawatt class laser. also used pump...
Experiments on the triatomic hydrogen molecular ion in intense ultrashort laser pulses are important for understanding fundamentals of polyatomic dynamics and providing a benchmark theory. Here we extend our earlier measurements [Phys. Rev. Lett. 103, 103004 (2009)] to provide comprehensive picture D${}_{3}$${}^{+}$ fragmentation 7- 40-fs, 790-nm at intensities up 10${}^{16}$ W/cm${}^{2}$. Our incorporate two- three-body coincidence three-dimensional momentum imaging involving crossed-beam...