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A systematic study was conducted to understand the size and shape of nanopatterns generated on selected semiconducting (Si and Ge) and metallic (Cr, Cu, and Ag) targets under different laser pulse durations, laser energies, and number of laser pulses. Based on the experimental results, femtosecond laser pulses, compared with nanosecond laser pulses, provide lower damage thresholds to the targets but higher damage thresholds to the near field scanning optical microscope (NSOM) probes at the wavelength (∼400–410 nm) studied. Furthermore, the resulting nanopatterns showed a significant dependence on the optical properties (i.e., absorption coefficient and surface reflectivity) of the target material. By comparing the obtained experimental results, we conclude that the optical energy transport from the NSOM probe to the target dominates the pattern generation when femtosecond laser is applied to the NSOM system. When nanosecond laser is applied, both the thermal and optical energy transported from the NSOM probe to the targets attribute to the obtained morphology of nanopatterns on different targets under the experimental conditions studied. [ABSTRACT FROM AUTHOR]

We investigate the distribution of atoms and diatomic metal-oxide molecules in femtosecond laser-induced plasmas generated at and after the laser beam focal plane, where non-linear phenomena give rise to the formation of a weakly ionized air plasma channel. We use direct plasma imaging and optical emission spectroscopy to study plasma expansion, and the associated physical and chemical separation processes. Plasma splitting occurs upon the interaction of the weakly ionized plasma with the sample and is accompanied by a change in the spatio-temporal distribution of the molecules and atoms compared to sampling at the focus. Furthermore, molecular emission is favored at specific locations and is enhanced over atomic emission as the sample is moved underneath the laser focus. These findings support the ability to enhance or impede the formation of molecular versus atomic species at specific spatio-temporal locations in the laser-induced plasma. [ABSTRACT FROM AUTHOR]

We utilized femtosecond laser ablation together with multi-collector inductively coupled plasma mass spectrometry to measure the uranium isotopic content of NIST 61x (x = 0, 2, 4, 6) glasses. The uranium content of these glasses is a linear two-component mixing between isotopically natural uranium and the isotopically depleted spike used in preparing the glasses. Laser ablation results match extremely well, generally within a few ppm, with solution analysis following sample dissolution and chemical separation. In addition to isotopic data, sample utilization efficiency measurements indicate that over 1% of ablated uranium atoms reach a mass spectrometer detector, making this technique extremely efficient. Laser sampling also allows for spatial analysis and our data indicate that rare uranium concentration inhomogeneities exist in NIST 616 glass. [ABSTRACT FROM AUTHOR]

We study the use of an ultraviolet (UV) femtosecond (fs)–nanosecond (ns) double-pulse scheme to improve the analytical capabilities of Laser Induced Breakdown Spectroscopy (LIBS) in the few-micron (＜2 μm) spatial resolution regime. We show that a double-pulse orthogonal configuration can enhance the spectral emission intensity by roughly 360 times as compared to a single-fs laser pulse LIBS of silicon (Si). Although the spectral emission lifetime in single-pulse LIBS is less than 20 ns, the second pulse provides signal enhancement hundreds of nanoseconds later, indicating that a significant number of non-radiative species (neutrals and/or particles) exist in these small length-scale plasmas long after the fs-laser pulse is over. The double-pulse configuration is a practical way to improve the limits of detection of LIBS for micron/submicron spatial resolution. [ABSTRACT FROM AUTHOR]

Direct chemical analysis of electrode/electrolyte interfaces can provide critical information on surface phenomena that define and control the performance of Li-based battery systems. In this work, we introduce the use of ex situ femtosecond laser induced breakdown spectroscopy to probe compositional variations within the solid electrolyte interphase (SEI) layer. Nanometer-scale depth resolution was achieved for elemental and molecular depth profiling of SEI layers formed on highly oriented pyrolytic graphite electrodes in an organic carbonate-based electrolyte. This work demonstrates the unique ability of ultrafast laser spectroscopy as a highly versatile, light element-sensitive technique for direct chemical analysis of interfacial layers in electrochemical energy storage systems. [ABSTRACT FROM AUTHOR]

Extending spatial resolution in laser-based chemical analysis to the nanoscale becomes increasingly important as nanoscience and nanotechnology develop. Implementation of femtosecond laser pulses arises as a basic strategy for increasing resolution since it is associated with spatially localized material damage. In this work we study femtosecond laser far- and near-field processing of silicon (Si) at two distinct wavelengths (400 and 800 nm), for nanoscale chemical analysis. By tightly focusing femtosecond laser beams in the far-field, we were able to produce sub-micrometer craters. In order to further reduce the crater size, similar experiments were performed in the near-field through sub-wavelength apertures, resulting in the formation of sub-30-nm craters. Laser-induced breakdown spectroscopy (LIBS) was used for chemical analysis with a goal to identify the minimum crater size from which spectral emission could be measured. Emission from sub-micrometer craters (full width at half maximum) was possible, which are among the smallest ever reported for femtosecond LIBS. [ABSTRACT FROM AUTHOR]

We study the effect of laser wavelength (400 and 800 nm) on the near-field processing of crystalline silicon (Si) in the femtosecond pulse duration regime through subwavelength apertures. Distinct differences in the obtained nanostructures are found in each case both in terms of their physical sizes as well as their structure, which can be tuned between craters and protrusions. A single or a few femtosecond pulses can deliver enough energy on the substrate to induce subdiffraction limited surface modification, which is among the smallest ever reported in subwavelength apertured near-field scanning optical microscope schemes. [ABSTRACT FROM AUTHOR]

While femtosecond Laser Induced Breakdown Spectroscopy has been studied in the macro-scale (i.e. ablation crater sizes of tens to hundreds of micrometers), the spectral emission mechanisms at the micron/sub-micron scale remain largely unknown, mainly because of the challenges associated with spectral emission acquisition from the limited amounts of ablated mass at these small lengthscales. In this work we study the limits of detection, the laser-induced plasma properties and spectral emission efficiency of Cu at the micron/submicron scale. Although the corresponding number electron densities and temperatures are similar to those reported for macroscale laser ablation, our findings suggest less efficient luminous spectral emission per ablated volume as we scale down in laser energy and crater sizes. These results provide a first insight into fs laser-induced plasma properties at the micron/sub-micron scale regime. [ABSTRACT FROM AUTHOR]

Abstract Chemical imaging applications using Laser Induced Breakdown Spectroscopy (LIBS) involve laser ablation sampling at interfaces or boundaries between materials with different thermophysical and optical properties, leading to the formation of two initially isolated plasmas. The mechanisms of mixing in these plasmas and their direct implications on spectral emission and chemical imaging remain largely unknown. We investigate the mixing dynamics of isolated plasmas produced using femtosecond (fs) laser pulses at the interface between two different model Cu and Sn Pb samples. Specifically, we study the spatial and temporal mixing dynamics and outer plasma expansion dynamics of the fs plasma components. The time-resolved degree of component mixing, horizontal and vertical expansion, mixing speed, and temperature and electron density of the heterogeneous plasma are characterized. Mixing processes are initiated early on, <100 ns after the laser pulse, and continue taking place until the end of plasma emission persistence at a constant velocity of 104 cm/s. These findings demonstrate that proper selection of detection timing parameters and signal collection position are critically important in precise LIBS measurements to ensure that full plasma mixing has taken place and that homogeneous spectral emission is properly detected. Graphical abstract Unlabelled Image Highlights • Mixing dynamics of isolated femtosecond (fs) plasmas at the interface between two different samples are studied. • Mixing processes start ≤100 ns after the laser pulse, and continue taking place until the end of plasma persistence. • Implications for chemical imaging applications using Laser Induced Breakdown Spectroscopy (LIBS) are evaluated. [ABSTRACT FROM AUTHOR]

Laser ablation molecular isotopic spectrometry (LAMIS) for rapid isotopic analysis of zirconium at atmospheric pressure was studied with a femtosecond-laser system operated under high repetition rate (1 kHz) and low pulse energy (160 μJ). The temporal evolution of zirconium neutral-atomic and ionic lines, as well as zirconium oxide molecular bands, were studied. Six molecular bands, belonging to the d3Δ-a3Δ (i.e., the α system) and E1Σ+-X1Σ+ transitions, were observed with appreciable isotopic shifts. The assignments of the isotopic bandheads were first based on theoretical predictions of the band origins and the associated isotopic shifts of various dipole-allowed ZrO electronic transitions, followed by an experimental confirmation with a 94Zr-enriched ZrO2 sample. In this work, the α(0,1) band from the d3Δ3-a3Δ3 subsystem was utilized for Zr isotope analysis based on a compromise between the magnitude of isotopic shifts in emission wavelengths, emission strengths, signal-to-background ratios, and spectral interferences. The analysis was performed in a standardless calibration approach; the isotopic information was extracted from the experimentally measured molecular spectra through theoretical spectral fitting. The results demonstrate the feasibility to obtain isotopic information for a spectrally complicated element like zirconium, without the need to use isotopically labeled calibration standards. The availability of comprehensive molecular constants will further improve the analytical accuracy of this standardless calibration approach. [ABSTRACT FROM AUTHOR]

This work reports that the composition of Cu(In,Ga)Se 2 (CIGS) thin solar cell films can be quantitatively predicted with high accuracy and precision by femtosecond laser ablation-inductively coupled plasma-mass spectrometry (fs-LA-ICP-MS). It is demonstrated that the results are strongly influenced by sampling conditions during fs-laser beam (λ = 1030 nm, τ = 450 fs) scanning on the CIGS surface. The fs-LA-ICP-MS signals measured at optimal sampling conditions generally provide a straight line calibration with respect to the reference concentrations measured by inductively coupled plasma optical emission spectroscopy (ICP-OES). The concentration ratios predicted by fs-LA-ICP-MS showed high accuracy, to 95–97% of the values measured with ICP-OES, for Cu, In, Ga, and Se elements. [ABSTRACT FROM AUTHOR]