We present the results of a systematic study of photoelectron emission from isolated dielectric nanoparticles (SiO₂) irradiated by intense 25 fs, 780 nm linearly polarized laser pulses as a function of particle size (20 nm to 750 nm in diameter) and laser intensity. We also introduce an experimental technique to reduce the effects of focal volume averaging. The highest photoelectron energies show a strong size dependence, increasing by a factor of six over the range of particles sizes studied at a fixed intensity. For smaller particle sizes (up to 200 nm), our findings agree well with earlier results obtained with few-cycle, ∼4 fs pulses. For large nanoparticles, which exhibit stronger near-field localization due to field-propagation effects, we observe the emission of much more energetic electrons, reaching energies up to ∼200 times the ponderomotive energy. This strong deviation in maximum photoelectron energy is attributed to the increase in ionization and charge interaction for many-cycle pulses at similar intensities.

In this paper, the effect of laser pulse energy on orthogonal double femtosecond pulse laser induced breakdown spectroscopy (LIBS) in air is studied. In the experiment, the energy of the probe pulse is changeable, while the pump pulse energy is held constant. At the same time, a systematic study of the laser induced breakdown spectroscopy signal dependence on the inter-pulse delay between the two pulses is performed. It is noted that the double pulse orthogonal configuration yields 2–32 times signal enhancement for the ionic and atomic lines as compared to the single pulse LIBS spectra when an optimum temporal separation between the two pulses is used, while there is no significant signal enhancement for the molecular lines in the studied range of the delay. It is also noted that the dependence of the enhancement factor for ionic and atomic lines on the inter-pulse delay can be fitted by Gaussian function. Furthermore, the electron temperature obtained by the relative line-to-continuum intensity ratio method was used to explain the LIBS signal enhancement.

The free expansion of a planar plasma surface is a fundamental non-equilibrium process relevant for various fields but as-yet experimentally still difficult to capture. The significance of the associated spatiotemporal plasma motion ranges from astrophysics and controlled fusion to laser machining, surface high-harmonic generation, plasma mirrors, and laser-driven particle acceleration. Here, we show that x-ray coherent diffractive imaging can surpass existing approaches and enables the quantitative real-time analysis of the sudden free expansion of laser-heated nanoplasmas. For laser-ionized SiO₂ nanospheres, we resolve the formation of the emerging nearly self-similar plasma profile evolution and expose the so far inaccessible shell-wise expansion dynamics including the associated startup delay and rarefaction front velocity. Our results establish time-resolved diffractive imaging as an accurate quantitative diagnostic platform for tracing and characterizing plasma expansion and indicate the possibility to resolve various laser-driven processes including shock formation and wave-breaking phenomena with unprecedented resolution.

The excitation of nanoscale near-fields with ultrashort and intense laser pulses of well-defined waveform enables strongly spatially and temporally localized electron emission, opening up the possibility for the generation of attosecond electron pulses. Here, we investigate the electron photoemission from isolated nanoparticles of different materials in few-cycle laser fields at intensities where the Coulomb field of the ionized electrons and residual ions significantly contribute to the electron acceleration process. The dependences of the electron cut-off energy on the material’s dielectric properties and electron binding energy are investigated systematically in both experiments and semi-classical simulations. We find that for sufficiently high near-field intensities the material dependence of the acceleration in the enhanced near-fields is quenched by many-particle charge-interaction.

A beam of 33 fs laser pulse with peak power of 15–40 GW was employed to explore a convenient method to determine the nonlinear refractive index coefficient of an optical glass. It is rare to investigate nonlinearities of optical glass with such an extreme ultrashort and powerful laser pulse. According to our method, only a single beam and a few experimental apparatuses are necessary to measure the nonlinear refractive index coefficient. The results from our method are in reasonable agreement with the others, which demonstrates that this new method works well, and the nonlinear refractive index coefficient is independent of measuring technology. Meanwhile, according to our results and those obtained by others in different laser power ranges, it seems that the nonlinear refractive index coefficient has a weak dependence on the laser peak power.