Controlling the dissociative ionization of ethanol with 800 and 400nm two-color femtosecond laser pulses

Exploring the influence of experimental parameters on the interaction of asymmetric ω/2ω fields with water isotopologues

Water isotopologues are doubly ionized by phase-controlled asymmetric ω/2ω laser fields, and their two-body fragmentation channels leading to pairs of OH⁺/H⁺ [channel (I)] and H₂ ⁺/O⁺ [channel (II)] are systematically investigated. The dependence of the ionic fragments on phase distinguishes between two dissociation channels, while a quantity that is proportional to the directionality of the ejected fragments, called asymmetry parameter (β), is measured as a function of composite field's phase. The dependence of the two channels' asymmetry amplitude (β₀) on the experimental parameters that characterize the composite field (wavelength, anisotropic shape, and total intensity) is found to differ significantly. The channel leading to H₂ ⁺ and O⁺ ions' ejection shows increased asymmetry compared to the other channel and is found to be dependent on excitation of overtones and combinations of vibrational modes as well as from the field's shape and intensity. The asymmetry (β) of the channel leading to the release of a H⁺ and an OH⁺ ions is far less sensitive to the experimental parameters. Inspection of the individual OH⁺ peak's dependence on phase reveals information on the effect of the field's profile, which is unclear when asymmetry (β) is inspected.

Controlling intramolecular hydrogen migration by asymmetric laser fields: the water case

Hydrogen and deuterium intramolecular migration in water's isotopomer dications has been found to depend on the wavelength of the laser used for the excitation. This is imprinted in H₂⁺ and D₂⁺ fragment ions' observation in the mass spectra induced by single color fs laser irradiation with 800 nm ≤λ≤ 1570 nm. Based on these findings, experiments with ω/2ω asymmetric laser fields (1400/700 nm) have been performed. The dissociation channels of the dications exhibit different dependence on the phase between the ω and 2ω components of the field thus offering an ability for controlling the fragmentation. For the interpretation of these observations, a tunneling mechanism is invoked.

Femtosecond Laser Produced Hydrophobic Hierarchical Structures on Additive Manufacturing Parts

With the recent expansion of additive manufacturing (AM) in industries, there is an intense need to improve the surface quality of AM parts. A functional surface with extreme wettability would explore the application of AM in medical implants and microfluid. In this research, we propose to superimpose the femtosecond (fs) laser induced period surface structures (LIPSS) in the nanoscale onto AM part surfaces with the micro structures that are fabricated in the AM process. A hierarchical structure that has a similar morphology to a lotus leaf surface is obtained by combining the advantages of liquid assisting fs laser processing and AM. A water contact angle (WCA) of 150° is suggested so that a super hydrophobic surface is achieved. The scanning electron microscopy (SEM) images and X-ray photoelectron spectroscopy (XPS) analysis indicate that both hierarchical structures and higher carbon content in the laser processed area are responsible for the super hydrophobicity.