Pranitha Sankar

White light Z-scan measurements of ultrafast optical nonlinearity in reduced graphene oxide nanosheets in the 400–700 nm region

Wavelength dispersion of optical power limiting is an important factor to be considered while designing potential optical limiters for laser safety applications. We report the observation of broadband, ultrafast optical limiting in reduced graphene oxide (rGO), measured by a single open aperture Z-scan using a white light continuum (WLC) source. WLC Z-scan is fast when the nonlinearity is to be measured over broad wavelength ranges, and it obviates the need for an ultrafast tunable laser making it cost-economic compared to conventional Z-scan. The nonlinearity arises from nondegenerate two-photon absorption, owing mostly to the crystallinity and extended π conjugation of rGO.

l-Glutamic acid functionalized silver nanoparticles and its nonlinear optical applications

Abstractl-Glutamic acid functionalized silver (Glu-Ag) nanoparticles (NPs) were synthesized in the aqueous medium and in a sol–gel matrix. Both samples showed different UV/Vis, zeta potential, TEM and SEM profiles. Surface enhanced raman spectra of the colloidal NPs reveal that the amino moiety of Glu is bound on the Ag surface with the charged carboxylate group pointing outwards. In contrast, in the sol–gel media, the attachment of Glu to the Ag NP surface was through the carboxylate group. Intensity-dependent nonlinear optical absorption measured using the open aperture Z-scan technique revealed that the aqueous solution of Glu-Ag is an efficient optical limiter.

Optical nonlinearity and charge transfer analysis of pyrene adsorbed on silver: Computational and experimental investigations

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.

Optical emission and dynamics of aluminum plasmas produced by ultrashort and short laser pulses

Optical emission and dynamics of ionized and neutral species present in plasmas generated by irradiating an aluminum target with ultrashort (100 fs) and short (7 ns) laser pulses is investigated, in the background pressure range of 10−2 to 760 Torr. Emission spectra exhibit lines from neutrals (Al I) as well as singly and doubly ionized ions (Al II, Al III). Maximum emission is seen in the pressure range of 10 to 20 Torr, around a distance of 1 mm from the target surface. While thermal ablation and laser–plasma interaction are prevalent in short pulse laser ablation (SLA), Coulomb explosion is prominent in ultrashort pulse laser ablation (ULA) because of the high optical intensity of the fs pulse. Ion population is an order of magnitude higher for SLA compared to ULA. Time of flight (TOF) studies reveal both fast and slow moving species in SLA, while this distinction is not quite obvious in ULA. Fast neutrals observed in SLA are formed by the recombination of fast ions with electrons. Space-charge effect in the expanding plasma and the associated Coulomb force results in the acceleration of charged particles, with ions reaching peak velocities up to 30 km s−1 in SLA. Velocities decrease at higher background pressures because of plume confinement. TOF data of Al neutrals fitted to shifted Maxwell–Boltzmann distributions indicate a general thermal nature, while the fast species in SLA appear to show a non-thermal behavior. Time-resolved ICCD images of the plasma depict a relatively rapid initial expansion for the SLA plume. These investigations provide valuable insights into the composition and expansion of Al plasmas produced by ultrashort and short laser pulses respectively, which might be of importance for a number of applications including EUV and X-ray generation, pulsed laser deposition, cluster production, and nanoparticle formation and growth.

Electronic and Nonlinear Optical Properties of l-Histidine on Silver: A Theoretical and Experimental Approach

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.