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Full-Text Articles in Physics

Ultrafast Resonance-Enhanced Multiphoton Ionization In The Azabenzenes: Pyridine, Pyridazine, Pyrimidine, And Pyrazine, Timothy D. Scarborough, David B. Foote,, Cornelis J. Uiterwaal Jan 2012

Ultrafast Resonance-Enhanced Multiphoton Ionization In The Azabenzenes: Pyridine, Pyridazine, Pyrimidine, And Pyrazine, Timothy D. Scarborough, David B. Foote,, Cornelis J. Uiterwaal

C.J.G.J. Uiterwaal Publications

We report on the ultrafast photoionization of pyridine, pyridazine, pyrimidine, and pyrazine. These four molecules represent a systematic series of perturbations into the structure of a benzene ring which explores the substitution of a C–H entity with a nitrogen atom, creating a heterocyclic structure. Data are recorded under intense-field, single-molecule conditions. The pulses (50 fs, 800 nm) are focused into the molecular vapor, and ion mass spectra are recorded for intensities of ∼1013 W/cm2 to ∼1015 W/cm2. We measure ion yields in the absence of the focal volume effect without the need for ...


Observation And Identification Of Metastable Excited States In Ultrafast Laser-Ionized Pyridine, David B. Foote, Timothy D. Scarborough, Cornelis J. Uiterwaal Jan 2012

Observation And Identification Of Metastable Excited States In Ultrafast Laser-Ionized Pyridine, David B. Foote, Timothy D. Scarborough, Cornelis J. Uiterwaal

C.J.G.J. Uiterwaal Publications

We report on the fragmentation of ionized pyridine (C5H5N) molecules by focused 50 fs, 800 nm laser pulses. Such ionization produces several metastable ionic states that fragment within the field-free drift region of a reflectron- type time of flight mass spectrometer, with one particular metastable dissociation being the leading fragmentation process. Because the time of flight is no longer dependent in a simple way on the mass of the ion, the metastable decay is manifested as an unfocused peak on the mass spectrum that appears at a time of flight not corresponding to an integer mass ...


Ultrafast Rempi In Benzene And The Monohalobenzenes Without The Focal Volume Effect, Timothy D. Scarborough, James Strohaber, David B. Foote, Collin J. Mcacy, Cornelis J. Uiterwaal Jan 2011

Ultrafast Rempi In Benzene And The Monohalobenzenes Without The Focal Volume Effect, Timothy D. Scarborough, James Strohaber, David B. Foote, Collin J. Mcacy, Cornelis J. Uiterwaal

C.J.G.J. Uiterwaal Publications

We report on the photoionization and photofragmentation of benzene (C6H6) and of the monohalobenzenes C6H5–X (X = F, Cl, Br, I) under intense-field, single-molecule conditions. We focus 50-fs, 804-nm pulses from a Ti:sapphire laser source, and record ion mass spectra as a function of intensity in the range ~1013 W/cm2 to ~1015 W/cm2. We count ions that were created in the central, most intense part of the focal area; ions from other regions are rejected. For all targets, stable parent ions (C6H5X+) are ...


Exploring Temporal And Rate Limits Of Laser-Induced Electron Emission, Shawn A. Hilbert, A. Neukirch, Cornelis J. Uiterwaal, Herman Batelaan Jan 2009

Exploring Temporal And Rate Limits Of Laser-Induced Electron Emission, Shawn A. Hilbert, A. Neukirch, Cornelis J. Uiterwaal, Herman Batelaan

C.J.G.J. Uiterwaal Publications

To achieve high temporal resolution for ultrafast electron diffraction, Zewail (Proc. Natl Acad. Sci. USA 102, 7069 (2005)) has proposed to use high repetition rate, ultrafast electron sources. Such electron sources emitting one electron per pulse eliminate Coulomb broadening. High repetition rates are necessary to achieve reasonable data acquisition times. We report laser-induced emission from a nanometre-sized tip at one electron per pulse with a 1 kHz repetition rate in the femtosecond regime. This source, combined with 1 MHz repetition rate lasers that are becoming available, will be a primary candidate for next generation ultrafast, high-coherence electron diffraction experiments. We ...


Temporal Lenses For Attosecond And Femtosecond Electron Pulses, Shawn A. Hilbert, Cornelis J. Uiterwaal, Brett E. Barwick, Herman Batelaan, Ahmed H. Zewail Jan 2009

Temporal Lenses For Attosecond And Femtosecond Electron Pulses, Shawn A. Hilbert, Cornelis J. Uiterwaal, Brett E. Barwick, Herman Batelaan, Ahmed H. Zewail

C.J.G.J. Uiterwaal Publications

Here, we describe the ‘‘temporal lens’’ concept that can be used for the focus and magnification of ultrashort electron packets in the time domain. The temporal lenses are created by appropriately synthesizing optical pulses that interact with electrons through the ponderomotive force. With such an arrangement, a temporal lens equation with a form identical to that of conventional light optics is derived. The analog of ray diagrams, but for electrons, are constructed to help the visualization of the process of compressing electron packets. It is shown that such temporal lenses not only compensate for electron pulse broadening due to velocity ...


Measurements Of The Gvd Of Water And Methanol And Laser Pulse Characterization Using Direct Imaging Methods, Timothy Scarborough, Chad Petersen, Cornelis J. Uiterwaal Jan 2008

Measurements Of The Gvd Of Water And Methanol And Laser Pulse Characterization Using Direct Imaging Methods, Timothy Scarborough, Chad Petersen, Cornelis J. Uiterwaal

C.J.G.J. Uiterwaal Publications

We report experimental values of the group velocity dispersion (GVD) of water and methanol at 800 nm. We find GVDwater 800 = (25.71± 0.5) fs2 mm−1 and GVDmethanol 800 = (33.56±0.5) fs2 mm-1. These were measured by sending 50 fs, 800 nm pulses with various amounts of chirp through a glass cell filled with a solution of fluorescein in these solvents and recording the production of visible light from the side using a commercial digital camera. This simple setup also gives quantitative information on the duration of our pulses and lets ...


Ultrashort Intense-Field Optical Vortices Produced With Laser-Etched Mirrors, James Strohaber, Timothy D. Scarborough, Cornelis J. Uiterwaal Dec 2007

Ultrashort Intense-Field Optical Vortices Produced With Laser-Etched Mirrors, James Strohaber, Timothy D. Scarborough, Cornelis J. Uiterwaal

C.J.G.J. Uiterwaal Publications

We introduce a simple and practical method to create ultrashort intense optical vortices for applications involving high-intensity lasers. Our method utilizes femtosecond laser pulses to laser etch grating lines into laser-quality gold mirrors. These grating lines holographically encode an optical vortex. We derive mathematical equations for each individual grating line to be etched, for any desired (integer) topological charge. We investigate the smoothness of the etched grooves. We show that they are smooth enough to produce optical vortices with an intensity that is only a few percent lower than in the ideal case. We demonstrate that the etched gratings can ...


A High Repetition Rate Time-Of-Flight Electron Energy Analyzer, Shawn A. Hilbert, Brett E. Barwick, M. Fabrikant, Cornelis J. Uiterwaal, Herman Batelaan Oct 2007

A High Repetition Rate Time-Of-Flight Electron Energy Analyzer, Shawn A. Hilbert, Brett E. Barwick, M. Fabrikant, Cornelis J. Uiterwaal, Herman Batelaan

C.J.G.J. Uiterwaal Publications

We demonstrate a time-of-flight electron energy analyzer that operates at an 80 MHz repetition rate. The analyzer yields an energy resolution of 40 meV for 3 eV electrons. The energy resolution limit is dominated by the detector time (or temporal) resolution. With a currently available detector with a temporal resolution of 100 ps, we predict an energy resolution of less than 1 meV for 200 meV electrons. This makes high repetition rate time-of-flight energy analyzers a promising low-technology alternative to current state-of-the-art techniques.


Efficient Angular Dispersion Compensation In Holographic Generation Of Intense Ultrashort Paraxial Beam Modes, James Strohaber, C. Petersen, Cornelis J. Uiterwaal Aug 2007

Efficient Angular Dispersion Compensation In Holographic Generation Of Intense Ultrashort Paraxial Beam Modes, James Strohaber, C. Petersen, Cornelis J. Uiterwaal

C.J.G.J. Uiterwaal Publications

We experimentally demonstrate that small misalignments of the pulse stretcher or compressor of our chirped-pulse-amplification laser can precompensate for angular chirp when producing ultrashort paraxial beam modes with holographic gratings. Using this approach we can eliminate one of the two gratings needed in our 2f–2f setup [Mariyenko et al., Opt. Express 13, 7599 (2005)]. This allows for up to an order of magnitude more output power. We see our method as the next step in the production of intense exotic forms of ultrashort pulses, which can be used in the investigation of intense laser–matter interactions. In ...


Tip-Top Imaging [Microscopy], Herman Batelaan, Cornelis J. Uiterwaal Mar 2007

Tip-Top Imaging [Microscopy], Herman Batelaan, Cornelis J. Uiterwaal

C.J.G.J. Uiterwaal Publications

Images of nanoscale structures can be constructed using the flow of electrons ejected from a metal probe tip by a fast laser pulse. The technique adds new dimensions to established methods of microscopy.


Creation Of Optical Vortices In Femtosecond Pulses, I. G. Mariyenko, James Strohaber, Cornelis J. Uiterwaal Sep 2005

Creation Of Optical Vortices In Femtosecond Pulses, I. G. Mariyenko, James Strohaber, Cornelis J. Uiterwaal

C.J.G.J. Uiterwaal Publications

We experimentally created a femtosecond optical vortex using a pair of computer-synthesized holographic gratings arranged in a 2f - 2f optical setup. We present measurements showing that the resulting donut mode is free of spatial chirp, and support this finding with an analysis of the optical wave propagation through our system based on the Kirchhoff- Fresnel diffraction integral. An interferogram confirms that our ultrashort vortex has topological charge 1, and a conservative experimental estimation of its duration is 280 fs. We used 25-fs radiation pulses (bandwidth approximately 40 nm) produced by a Ti:sapphire laser oscillator.


White-Light-Induced Fragmentation Of Toluene, A. M. Müller, B. Witzel, Cornelis J. Uiterwaal, J. Wanner, K.-L. Kompa Jan 2002

White-Light-Induced Fragmentation Of Toluene, A. M. Müller, B. Witzel, Cornelis J. Uiterwaal, J. Wanner, K.-L. Kompa

C.J.G.J. Uiterwaal Publications

We investigate the influence of continuum generation on the photofragmentation dynamics of the toluene molecule. By sending an 80-fs Ti:sapphire laser beam through a 2-mm-thick CaF2 plate we show that even moderately broadened laser frequency spectra considerably increase the degree of fragmentation, while it is nearly absent without continuum generation. The measured broadening of the frequency spectra and the known Raman-active vibrational modes of toluene afford an explanation in terms of a stimulated Raman scattering scheme, in which the molecule absorbs large amounts of vibrational energy.


Photoionization And Photofragmentation Of Gaseous Toluene Using 80-Fs, 800-Nm Laser Pulses, A. M. Müller, Cornelis J. Uiterwaal, B. Witzel, J. Wanner, K.-L. Kompa Jun 2000

Photoionization And Photofragmentation Of Gaseous Toluene Using 80-Fs, 800-Nm Laser Pulses, A. M. Müller, Cornelis J. Uiterwaal, B. Witzel, J. Wanner, K.-L. Kompa

C.J.G.J. Uiterwaal Publications

This paper presents ion yields resulting from multiphoton ionization and fragmentation of gaseous toluene (C7H8) in the focus of an 80 fs Ti:sapphire laser beam (λ = 800 nm) with a sufficiently small B-integral [Siegman, Lasers (University Science Books, Mill Valley, CA, 1986)]. The peak intensity was varied between 1.9x1013 and 2.8x1013Wcm-2, and both linear and circular polarization were used. Over the whole range of intensities studied, only the singly charged parent ion and its fragment, C7H7+, are found. Although the Keldysh adiabaticity parameter equals 0.86 ...


Multiphoton Ionization Of V, Cr, Y, La, And Ir Through 0.5-Ps Ultraviolet Laser Pulses, B. Witzel, N. A. Poppadogiannis, Cornelis J. Uiterwaal, H. Schröder, D. Charalambidis Oct 1999

Multiphoton Ionization Of V, Cr, Y, La, And Ir Through 0.5-Ps Ultraviolet Laser Pulses, B. Witzel, N. A. Poppadogiannis, Cornelis J. Uiterwaal, H. Schröder, D. Charalambidis

C.J.G.J. Uiterwaal Publications

The two-photon ionization of the metal atoms V, Cr, Y, La, and Ir sputtered by an Ar-ion gun from solid targets has been investigated using linearly polarized laser pulses of 500- fs duration and 248.6-nm (KrF) wavelength in combination with mass spectroscopy that is free of volume effects. A near-resonant ionization process has to be attributed to all five atoms. By fitting analytical solutions of a rate equation model describing the temporal evolution of the ionization process, we can determine absolute values of the one-photon cross sections and saturation intensities.


Analysis Of Multiphoton Ionization Of Metal Atoms In The Saturation Regime Using Subpicosecond Krf Laser Pulses, B. Witzel, Cornelis J. Uiterwaal, H. Schröder, D. Charalambidis, K.-L. Kompa Nov 1998

Analysis Of Multiphoton Ionization Of Metal Atoms In The Saturation Regime Using Subpicosecond Krf Laser Pulses, B. Witzel, Cornelis J. Uiterwaal, H. Schröder, D. Charalambidis, K.-L. Kompa

C.J.G.J. Uiterwaal Publications

Singly and multiply charged ion yield curves are reported for resonant and nonresonant two photon- ionization processes for a collection of 31 metal atoms. The atoms are created by sputtering from a solid target using an Ar-ion gun. Single and multiple ionization of these atoms is performed using linearly polarized 248.6-nm (KrF) laser pulses with a full width at half maximum duration of 500 fs, employing intensities between 109 and 1012 W cm-2. A four-grid high-resolution reflecting time-of-flight spectrometer is used for ion detection. This advanced spectrometer has a well-defined and small source volume, enabling absolute ...


Self-Calibrating Method For Measuring Local Multiphotonionization Yields As A Function Of Absolute Intensity, Cornelis J. Uiterwaal, B. Witzel, H. Schröder, K.-L. Kompa Aug 1998

Self-Calibrating Method For Measuring Local Multiphotonionization Yields As A Function Of Absolute Intensity, Cornelis J. Uiterwaal, B. Witzel, H. Schröder, K.-L. Kompa

C.J.G.J. Uiterwaal Publications

We present a self-calibrating method for measuring local multiphoton-ionization yields as a function of absolute intensity. In contrast to the method recently described by Walker et al. [Phys. Rev. A 57, R701 (1998)], our method does not require any assumption on the intensity distribution inside a laser focus, nor does it use any mathematical procedure such as deconvolution that would be based on such an assumption. In this sense, our method is self-calibrating. The proposed method immediately gives ion yields as a function of absolute intensity. Furthermore, it allows the intensity distribution inside the focal volume to be measured with ...


Generalized Multiphoton-Ionization Cross Sections Of The Rare Gases For 500-Fs, 248.6-Nm Pulses, Cornelis J. Uiterwaal, D. Xenakis, D. Charalambidis, P. Maragakis, H. Schröder, P. Lambropoulus Jan 1998

Generalized Multiphoton-Ionization Cross Sections Of The Rare Gases For 500-Fs, 248.6-Nm Pulses, Cornelis J. Uiterwaal, D. Xenakis, D. Charalambidis, P. Maragakis, H. Schröder, P. Lambropoulus

C.J.G.J. Uiterwaal Publications

Absolute values for the generalized multiphoton-ionization cross sections and saturation intensities of rare gases are reported for 500-fs, 248.6-nm pulses. For He, Ar, and Kr these values are experimentally determined from the intensity dependence of the ponderomotive shift for intensities comparable to and above the saturation intensity. The measured experimental cross sections [σ(5)He=(0.9+9-o.4)×10-152 cm10 s4, σ(4)Ar=(1.3+1-0.5)×10-116 cm8 s3, σ(5)Kr=(1.2+1.7-0.6)×10-82 cm6 s2, σ(3)Xe=(50 ...


Effects Of Coherent Coupling Of Autoionizing States On Multiphoton Ionization, N. E. Karapanagioti, D. Charalambidis, Cornelis J. Uiterwaal, C. Fotakis, H. Bachau, I. Sanchez, E. Cormier Apr 1996

Effects Of Coherent Coupling Of Autoionizing States On Multiphoton Ionization, N. E. Karapanagioti, D. Charalambidis, Cornelis J. Uiterwaal, C. Fotakis, H. Bachau, I. Sanchez, E. Cormier

C.J.G.J. Uiterwaal Publications

We present the experimental and theoretical investigation of the effects of the strong electromagnetic coupling of two autoionizing states (AIS’s) on the photoionization properties of an atomic system. These effects are observed by probing the ladder system from the ground state of the atom through a weak two-photon transition to the region of the lower AIS. The experimental observation of the modification of the total ionization and partial photoelectron spectra at different wavelengths of the coupling and probe lasers are accurately reproduced by a theoretical analysis which uses a density-matrix approach. Both theory and experiment indicate a strong inhibition ...


State-Selected Ion-Molecule Reactions: Statistical Calculations With Constraints, Cornelis J. Uiterwaal, J. Van Eck, A. Niehaus May 1995

State-Selected Ion-Molecule Reactions: Statistical Calculations With Constraints, Cornelis J. Uiterwaal, J. Van Eck, A. Niehaus

C.J.G.J. Uiterwaal Publications

For the two reactive systems, NH3+(Eint)+N H3→NH4++NH2 and H2+ (Eint)+H2→H3+ + H, for which the relative cross sections were measured earlier in our group for Ec.m.≈40 meV we calculated the relative cross section as a function of internal energy using the statistical Rice– Ramsperger–Kassel–Marcus (RRKM) theory that implicitly conserves total energy and total angular momentum. We found satisfactory agreement between theory and experiment by imposing rather mild constraints upon the loose transition state configuration. These constraints involve inactive vibrations and steric ...


State-Selected Ion-Molecule Reactions: Charge Transfer And Atomic Rearrangement Processes In Thermal Energy Collisions Of H2+ (X;V)+N2 And Of N2+ (X,A;V) + H2, Cornelis J. Uiterwaal, J. Van Eck, A. Niehaus Jan 1995

State-Selected Ion-Molecule Reactions: Charge Transfer And Atomic Rearrangement Processes In Thermal Energy Collisions Of H2+ (X;V)+N2 And Of N2+ (X,A;V) + H2, Cornelis J. Uiterwaal, J. Van Eck, A. Niehaus

C.J.G.J. Uiterwaal Publications

Using the photo-electron-product-ion-coincidence method (PEPICO) we have measured state-selective cross sections for the following processes: (A) N2+ (X,A;v)+ H2→N2H+ + H, (B) H2+ (X;v) + N2→N2H+ + H, (C) N2+ (X,A;v)+H2→H2+ + N2, and (D) H2+ (X;v)+N2→N2+ + H2 . The measurements were performed at thermal velocities (Ec.m. ≈ 40 meV).We have found that the charge transfer processes (C) and (D) have cross sections that are at least an order of magnitude smaller than the cross ...