The effect of the laser pulse width on the production of nanoparticles by laser fragmentation was investigated. Laser pulse widths of 164 fs, 5 ps, 4 ns, 36 ns, 64 ns, and 100 ns were used. To assess the effect of the laser pulse width on the energy distribution in the nanoparticles, the energy distribution was simulated using wave optics. Silver (Ag) nanoparticles were produced by laser irradiation of an Ag target in distilled water. The wavelength of the femtosecond, picosecond, and nanosecond lasers used was 1070 nm, and their fluences were 0.10–0.13 mJ/cm². Nanoparticle microstructure was visualized by transmission electron microscopy and scanning electron microscopy, and the nanoparticle size distribution was evaluated using a particle size analyzer.

Kim J, et al. J Korean Med Sci. 2015 Nov;30(11):1667-1674. https://doi.org/10.3346/jkms.2015.30.11.1667

In a laser-induced breakdown spectroscopy (LIBS) system that performs elemental analysis of a target by acquiring the emission of plasma generated on the material surface by a focused laser, the plasma signal may be affected by the flow of the surrounding gas. A flow of gas may be present when LIBS measurements are performed in a special environment where an inert gas is normally applied. In such an environment, the flow of gas may affect the intensity of emission generated in plasma. The LIBS spectral intensity in the gas flow field changes according to the direction of the gas flow and the signal detector of the LIBS. In this case, the correlation between the flow rate and intensity of the spectral line can be confirmed both theoretically and experimentally. In this study, changes in the signal according to the flow rate were theoretically evaluated using the view factor and wave equation. In addition, LIBS signals were examined based on the flow of Ar, N₂, and He gases in the experiment. The experimental results confirmed the range of effective gas flow rates over which the correlation between the flow rate and intensity of the LIBS spectral line could be inferred. These results could be used for calibration to achieve accurate measurement of LIBS signals in gas flow fields. In addition, this analysis has the potential to shed light on the properties of flowing gases that affect plasma by reversibly tracking changes in the signal of LIBS in a confined environment.

Heterogeneous Ag/Au nanoparticles combined with Pd ions were generated by irradiating Ag/Au metal targets in a Pd solution with nanosecond and femtosecond lasers. AgPd and AuPd nanoparticles were generated by laser fragmentation and bonded. We numerically analyzed the hot spots with electromagnetic field enhancement of nanoparticles of different sizes separated by various distances. AgPd and AuPd nanoparticles differing in diameter were generated and showed different characteristics compared to typical core-shell heterogeneous nanoparticles. Pd ions played an important role in the generation of nanoparticles in liquid via laser ablation. The femtosecond laser produced both pure and heterogeneous nanoparticles of uniform size. The nanosecond laser produced pure nanoparticles with a relatively non-uniform size, which developed into spherical heterogeneous nanoparticles with a uniform (small) size in the presence of Pd ions. These nanoparticles could optimize applications such as photothermal therapy and catalysis.