Matthew Weidman

Nd:YAG-CO 2 double-pulse laser induced breakdown spectroscopy of organic films

Laser-induced breakdown spectroscopy (LIBS) using double-pulse irradiation with Nd:YAG and CO(2) lasers was applied to the analysis of a polystyrene film on a silicon substrate. An enhanced emission signal, compared to single-pulse LIBS using a Nd:YAG laser, was observed from atomic carbon, as well as enhanced molecular emission from C(2) and CN. This double-pulse technique was further applied to 2,4,6-trinitrotoluene residues, and enhanced LIBS signals for both atomic carbon and molecular CN emission were observed; however, no molecular C(2) emission was detected.

Stand-off filament-induced ablation of gallium arsenide

Using femtosecond filaments for the ablation of GaAs in air, we have observed that the diameter and volume of the resulting ablation craters remained almost constant with propagation distance. This constant mass removal along the propagation of a filament in both focused and non-focused configurations is valuable for applications such as material processing and stand-off laser-ablation based spectroscopy.

Molecular signal as a signature for detection of energetic materials in filament-induced breakdown spectroscopy

Laser Induced Breakdown Spectroscopy (LIBS) by self-channeled femtosecond pulses is characterized for detection of energetic materials. Different polymers are spin coated on silicon wafers to provide a thin organic layer with controllable thickness ranging from 500 nm to 1 μm. Spectral analysis of atomic and molecular carbon emission shows CN molecular signal from samples that do not contain nitrogen. This can be explained by possible molecular recombination between native atomic carbon and atmospheric nitrogen. As a consequence, caution must be exercised when using spectral signatures based on CN emission for explosive detection by filament-induced LIBS.

Next Generation Driver for Attosecond and Laser-plasma Physics

The observation and manipulation of electron dynamics in matter call for attosecond light pulses, routinely available from high-order harmonic generation driven by few-femtosecond lasers. However, the energy limitation of these lasers supports only weak sources and correspondingly linear attosecond studies. Here we report on an optical parametric synthesizer designed for nonlinear attosecond optics and relativistic laser-plasma physics. This synthesizer uniquely combines ultra-relativistic focused intensities of about 1020 W/cm2 with a pulse duration of sub-two carrier-wave cycles. The coherent combination of two sequentially amplified and complementary spectral ranges yields sub-5-fs pulses with multi-TW peak power. The application of this source allows the generation of a broad spectral continuum at 100-eV photon energy in gases as well as high-order harmonics in relativistic plasmas. Unprecedented spatio-temporal confinement of light now permits the investigation of electric-field-driven electron phenomena in the relativistic regime and ultimately the rise of next-generation intense isolated attosecond sources.

Generation of High-Energy Isolated Attosecond Pulses for XUV-pump/XUV-probe Experiments at 100 eV

We report on the generation of high-order harmonics in gas media using a sub-5 fs multi-ten-terawatt laser system. The application of this source towards XUV-pump/XUV-probe experiments with photon energies around 100 eV is discussed.

Tabletop nonlinear optics in the 100-eV spectral region

Nonlinear light-matter interactions in the extreme ultraviolet (XUV) are a prerequisite to perform XUV-pump/XUV-probe spectroscopy of core electrons. Such interactions are now routinely investigate ...

Investigation of high harmonic generation using a high-power, 5-fs laser in a loose-focusing geometry

Since its first observation almost three decades ago high-order harmonic generation (HHG) in gases became a reliable source of extreme ultraviolet (XUV) pulses, which gave the possibility to study electronic processes on their natural timescale [1, 2]. While the main building blocks of the experimental setups for gas HHG are the same in almost all cases, the focusing or medium geometry varies from realization to realization based on, for example, the available laser power [3, 4].

Towards attosecond XUV-pump XUV-probe measurements in the 100-eV region

Nonlinear photoionization with energetic FEL pulses has opened up new horizons for the investigation of inner-shell electron dynamics in atomic and molecular systems [1]. So far, however, the limited temporal resolution (typically a few tens of femtoseconds) achievable with FELs has hampered the time resolution of these dynamics.

Angular dependence of filament-induced plasma emission from a GaAs surface.

Quantitative measurements of the angular distribution of the plasma line emission from a gallium arsenide (GaAs) target irradiated by a single laser-air filament are reported. These enable reliable estimates of the stand-off ranges possible with single-filament-induced laser-induced breakdown spectroscopy materials detection.

Broadband THz detection in the counter-propagating configuration using THz-enhanced plasma fluorescence

Terahertz-Radiation Enhanced Emission of Fluorescence (THz-REEF) was studied in the counter-propagating configuration as a more accurate representation of stand-off THz sensing scenarios. Determination of the THz amplitude and phase using this technique was successfully demonstrated.