MeV photoelectron spectrometer for ultraintense laser interactions with atoms and molecules.

Traditional laser-matter spectroscopy techniques fail to accurately analyze photoelectrons and ions from ultrahigh intensity studies with terawatt and petawatt laser systems. We present a magnetic deflection, photoelectron spectrometer for ultrahigh intensity laser interactions with atoms and molecules in the single atom/molecule limit. Spectrometer fabrication and calibration, and noise background are presented as well as example photoelectron spectra for argon and chloromethane over an energy range from 20 keV to 2 MeV.

Limits of Strong Field Rescattering in the Relativistic Regime.

Recollision for a laser driven atomic system is investigated in the relativistic regime via a strong field quantum description and Monte Carlo semiclassical approach. We find the relativistic recollision energy cutoff is independent of the ponderomotive potential U_{p}, in contrast to the well-known 3.2U_{p} scaling. The relativistic recollision energy cutoff is determined by the ionization potential of the atomic system and achievable with non-negligible recollision flux before entering a "rescattering free" interaction. The ultimate energy cutoff is limited by the available intensities of short wavelength lasers and cannot exceed a few thousand Hartree, setting a boundary for recollision based attosecond physics.

Contamination-free solutions of selenium in amines for nanoparticle synthesis.

We present, for the first time, versatile solutions of concentrated selenium, within an array of amines, in a fast and low temperature manner without contaminants. These solutions allow the unprecedented opportunity to synthesize a variety of pure selenium and selenide nanoparticles as well as mixed chalcogen sulfoselenide compounds.

Electron shell ionization of atoms with classical, relativistic scattering.

We investigate forward scattering of ionization from neon, argon, and xenon in ultrahigh intensities of 2 × 10(19) W/cm(2). Comparisons between the gases reveal the energy of the outgoing photoelectron determines its momentum, which can be scattered as far forward as 45° from the laser wave vector k(laser) for energies greater than 1 MeV. The shell structure in the atom manifests itself as modulations in the photoelectron yield and the width of the angular distributions. We arrive at an agreement with theory by using an independent electron model for the atom, a dipole approximation for the bound state interaction, and a relativistic, three-dimensional, classical radiation field including the laser magnetic field. The studies provide the atomic physics within plasmas, radiation, and particle acceleration in ultrastrong fields.

Relativistic MeV photoelectrons from the single atom response of argon to a 10 19 W/cm2 laser field.

We present photoelectron measurements from argon ionization at 10(19) W/cm(2). Photoelectrons with energies above 400 keV, including a 1.2 MeV cutoff, are in quantitative agreement with a semiclassical, relativistic 3D ionization model that includes a nonparaxial laser field. L-shell photoelectrons have energies and momentum dominated by the field, including the acceleration out of the focus. Yields and angular distributions at 60 keV come from valence shell ionization by strong fields where rescattering and atomic processes determine photoelectron final states.

Ionization of methane in strong and ultrastrong relativistic fields.

The photoionization of methane is reported for intensities up to 10(19) W/cm2 with linear and circular polarized light. While fragmental ions (e.g., CH3+, CH+, C+, C2+) created from 10(14) W/cm2 to 10(15) W/cm2 are formed by Coulomb explosion, ionization to form C3+ and C4+ involves Coulomb explosion and tunneling ionization. In ultrastrong fields, removal of a carbon K-shell electron from methane proceeds via tunneling and rescattering ionization, without the influence of molecular channels. Photoelectrons from methane at 10(19) W/cm2 extend up to kinetic energies of 0.6 MeV.

0.09-terawatt pulses with a 31% efficient, kilohertz repetition-rate Ti:sapphire regenerative amplifier.

We present an efficient, ultrafast regenerate amplifier that increases the energy of a laser pulse from 300 pJ to 6 mJ and produces average powers of as much as 9 W in a TEM(00) spatial mode. As an ultrafast amplifier, the system produces 4-mJ pulses with 0.09 TW of peak power.

Community outreach at biomedical research facilities.

For biomedical researchers to fulfill their responsibility for protecting the environment, they must do more than meet the scientific challenge of reducing the number and volume of hazardous materials used in their laboratories and the engineering challenge of reducing pollution and shifting to cleaner energy sources. They must also meet the public relations challenge of informing and involving their neighbors in these efforts. The experience of the Office of Community Liaison of the National Institutes of Health (NIH) in meeting the latter challenge offers a model and several valuable lessons for other biomedical research facilities to follow. This paper is based on presentations by an expert panel during the Leadership Conference on Biomedical Research and the Environment held 1--2 November 1999 at NIH, Bethesda, Maryland. The risks perceived by community members are often quite different from those identified by officials at the biomedical research facility. The best antidote for misconceptions is more and better information. If community organizations are to be informed participants in the decision-making process, they need a simple but robust mechanism for identifying and evaluating the environmental hazards in their community. Local government can and should be an active and fully informed partner in planning and emergency preparedness. In some cases this can reduce the regulatory burden on the biomedical research facility. In other cases it might simplify and expedite the permitting process or help the facility disseminate reliable information to the community. When a particular risk, real or perceived, is of special concern to the community, community members should be involved in the design, implementation, and evaluation of targeted risk assessment activities. Only by doing so will the community have confidence in the results of those activities. NIH has involved community members in joint efforts to deal with topics as varied as recycling and soil testing. These ad hoc efforts are more likely to succeed if community members and groups have also been included in larger and longer term advisory committees. These committees institutionalize the outreach process. This can provide the facility with vocal and influential allies who create an independent line of communication with the larger community.