ABSTRACT
A large range of laser-matter applications employ ultrashort pulses and high laser intensity. Such processes can lead to unrequired X-ray generation, which represents a hazardous radiation factor even for common laboratory research-grade laser systems. We present here an analysis of the radiation dose rate and X-ray spectrum emitted during ablation of a rotating copper cylinder with respect to several laser parameters. The results show that focused sub-picosecond pulses with intensity above 1013 W/cm2 can exceed the annual irradiation limit even in one hour, requiring appropriate shielding for the safety of the researchers.
ABSTRACT
Ultrashort pulse laser machining is subject to increase the processing speeds by scaling average power and pulse repetition rate, accompanied with higher dose rates of X-ray emission generated during laser-matter interaction. In particular, the X-ray energy range below 10 keV is rarely studied in a quantitative approach. We present measurements with a novel calibrated X-ray detector in the detection range of 2-20 keV and show the dependence of X-ray radiation dose rates and the spectral emissions for different laser parameters from frequently used metals, alloys, and ceramics for ultrafast laser machining. Our investigations include the dose rate dependence on various laser parameters available in ultrafast laser laboratories as well as on industrial laser systems. The measured X-ray dose rates for high repetition rate lasers with different materials definitely exceed the legal limitations in the absence of radiation shielding.
ABSTRACT
An investigation of the electrostatic interactions between histidine and silver have been analyzed using density functional theory (DFT). Variations in the structural parameters were identified to be significant at those atoms of histidine near the silver cluster. The shifting of frontier molecular orbitals, reduction in bandgap, molecular electrostatic potential (MEP), and overlap of natural bond orbitals (NBO) between silver and histidine have been theoretically calculated. The results confirm the redistribution of charges consequent to the process of adsorption. On the basis of time-dependent density functional theory (TDDFT), two peaks were generated at 301 and 409 nm in the simulated UV-vis spectrum. Theoretical vibrational Raman analysis of the investigated molecules strongly confirms the process of adsorption. Nonlinear optical (NLO) properties are predicted by theoretical studies and confirmed experimentally via open-aperture Z-scan. The adsorption of histidine on silver enhances the NLO parameters, indicating that it is a promising candidate for NLO devices.
ABSTRACT
The interaction of pyrene on silver has been investigated using both experimental and computational methods. Hyperpolarizabilities computed theoretically together with experimental nonlinear absorption from open aperture Z-scan measurements, point towards a possible use of pyrene adsorbed on silver in the rational design of NLO devices. Presence of a red shift in both simulated and experimental UV-Vis spectra confirms the adsorption on silver, which is due to the electrostatic interaction between silver and pyrene, inducing variations in the structural parameters of pyrene. Fukui calculations along with MEP plot predict the electrophilic nature of the silver cluster in the presence of pyrene, with NBO analysis revealing that the adsorption causes charge redistribution from the first three rings of pyrene towards the fourth ring, from where the 2p orbitals of carbon interact with the valence 5s orbitals of the cluster. This is further confirmed by the downshifting of ring breathing modes in both the experimental and theoretical Raman spectra.
