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Sample ablation by pulsed lasers is one option for removing material from a sample surface for in situ depth profiling during imaging mass spectrometry, but ablation is often limited by laser-induced damage of the remaining material. A preliminary evaluation was performed of sub-100-fs, 800 nm pulsed laser ablation for depth profiling of bacterial biofilms grown on glass by the drip flow method. Electron and optical microscopy were combined with laser desorption vacuum ultraviolet postionization mass spectrometry to analyze biofilms before and after ablation. Ultrashort laser pulses can ablate 10–100 μm thick sections of bacterial biofilms, leaving behind a layer of lysed cells. However, mass spectra from intact and ablated biofilms doped with antibiotic are almost identical, indicating little chemical degradation by ablation. These results are consistent with prior observations from laser surgery and support the use of ultrashort pulse laser ablation for minimally disruptive depth profiling of bacterial biofilms and intact biological samples. [ABSTRACT FROM AUTHOR]

We report nearly completely polarized emission from the plasma produced in the femtosecond ablation of Si(111). Pairs of ultrashort laser pulses were focused onto the target in air, and the polarization spectrum was measured as a function of energy, pulse delay, and polarization state of the laser. When the laser was focused on the surface, the fluorescence continuum was strongly polarized, whereas discrete lines appeared as minima in the polarization spectrum. Under this focusing condition, the continuum polarization increased with pulse delay and decreased with pulse energy and fluorescence wavelength, with >95% polarization in the ultraviolet. [ABSTRACT FROM AUTHOR]

An ultrafast laser ablation time-of-flight mass spectrometer (AToF-MS) and associated data acquisition software that permits imaging at micron-scale resolution and sub-micron-scale depth profiling are described. The ion funnel-based source of this instrument can be operated at pressures ranging from 10-8 to ∼0.3 mbar. Mass spectra may be collected and stored at a rate of 1 kHz by the data acquisition system, allowing the instrument to be coupled with standard commercial Ti:sapphire lasers. The capabilities of the AToF-MS instrument are demonstrated on metal foils and semiconductor wafers using a Ti:sapphire laser emitting 800 nm, ∼75 fs pulses at 1 kHz. Results show that elemental quantification and depth profiling are feasible with this instrument. [ABSTRACT FROM AUTHOR]

Abstract: Several studies have appeared in the past two years reporting that the continuum emission produced by the laser ablation of solid materials is strongly polarized. In a paper that appears to conflict with these findings, Asgill et al. report that they did not observe a significant amount of polarization produced by nanosecond laser excitation of nitrogen gas and laser ablation of copper and steel ( M.E. Asgill, H.Y. Moon, N. Omenetto, D.W. Hahn, Investigation of polarization effects for nanosecond laser-induced breakdown spectroscopy, Spectrochim. Acta Part B (2010) xxx–xxx [7]). Here we show that the apparent discrepancy is resolved when laser fluence and polarization are taken into account. Using a 532nm Nd:YAG laser to ablate Al samples in air, we find that the degree of polarization, P, of the continuum is greater for s- vs. p-polarized excitation and that P decreases with increasing fluence. We show that P would be <10% under the conditions of Asgill et al., whereas P>60% is obtained at low fluences with s-polarized excitation. We also confirm that at high fluence the polarization of the discrete emission is much smaller than that of the continuum. [Copyright &y& Elsevier]

Experiments were performed to examine the feasibility of mass spectrometry (MS) depth profiling of animal tissue by ∼75 fs, 800 nm laser pulses to expose underlying layers of tissue for subsequent MS analysis. Matrix assisted laser desorption ionization mass spectrometry (MALDI-MS) was used to analyze phospholipids and proteins from both intact bovine eye lens tissue and tissue ablated by ultrashort laser pulses. Laser desorption postionization mass spectrometry (LDPI-MS) with 10.5 eV single photon ionization was also used to analyze cholesterol and other small molecules in the tissue before and after laser ablation. Scanning electron microscopy was applied to examine the ablation patterns in the tissue and estimate the depth of the ablation craters. Ultrashort pulse laser ablation was found to be able to remove a layer of several tens of micrometers from the surface of eye lens tissue while leaving the underlying tissue relatively undamaged for subsequent MS analysis. MS analysis of cholesterol, phospholipids, peptides, and various unidentified species did not reveal any chemical damage caused by ultrashort pulse laser ablation for analytes smaller than ∼6 kDa. However, a drop in intensity of larger protein ions was detected by MALDI-MS following laser ablation. An additional advantage was that ablated tissue displayed up to an order of magnitude higher signal intensities than intact tissue when subsequently analyzed by MS. These results support the use of ultrashort pulse laser ablation in combination with MS analysis to permit depth profiling of animal tissue. [ABSTRACT FROM AUTHOR]

Abstract: Three-dimensional micropatterned collagen scaffolds were fabricated by femtosecond laser ablation. An 800nm, 45fs Ti:Sapphire laser was used to create various 3D patterns in a collagen gel, including holes, lines and grids. An optimal collagen concentration was found for both substrate patterning and cell compatibility. The threshold fluence for ablation of the scaffold was found to be 0.06J/cm2, and the morphology of the ablation craters was measured as a function of fluence. Mesenchymal stem cells from rat bone marrow and human fibroblasts were seeded within the ablated patterns and were shown to be viable for at least 10 days. [Copyright &y& Elsevier]