Automated nanosecond laser pulse-induced heating, melting and acoustics in tungsten using two-wave mixing photorefractive interferometry

To ensure safety and high efficiency operation of nuclear power plants it is important to measure precisely and accurately solid-to-liquid phase transition and corresponding melting point temperature of nuclear fuels. Measurement of thermo-physical material properties of fresh and irradiated nuclear fuels is a key to understand, model and predict the performance of existing fuels and to develop new forms of fuels

Automated nanosecond laser pulse-induced heating, melting and acoustics in tungsten using two-wave mixing photorefractive interferometry

To ensure safety and high efficiency operation of nuclear power plants it is important to measure precisely and accurately solid-to-liquid phase transition and corresponding melting point temperature of nuclear fuels. Measurement of thermo-physical material properties of fresh and irradiated nuclear fuels is a key to understand, model and predict the performance of existing fuels and to develop new forms of fuels

Elastic and structural properties of sputtered refractory metal thin films

To fabricate optimal hard and wear-resistant coatings it is necessary to tailor their mechanical and structural properties for an optimal industrial application. We are exploring elastic and structural properties of refractory metal (Ta, Nb, Mo and W) thin films of different thicknesses fabricated by DC magnetron spattering technique on single crystalline Si substrates

Examination of nanosecond laser melting thresholds in refractory metals by shear wave acoustics

Nanosecond laser pulse-induced melting thresholds in refractory (Nb, Mo, Ta and W) metals are measured using detected laser-generated acoustic shear waves. Obtained melting threshold values were found to be scaled with corresponding melting point temperatures of investigated materials displaying dissimilar shearing behavior. The experiments were conducted with motorized control of the incident laser pulse energies with small and uniform energy increments to reach high measurement accuracy and real-time monitoring of the epicentral acoustic waveforms from the opposite side of irradiated sample plates. Measured results were found to be in good agreement with numerical finite element model solving coupled elastodynamic and thermal conduction governing equations on structured quadrilateral mesh. Solid-melt phase transition was handled by means of apparent heat capacity method. The onset of melting was attributed to vanished shear modulus and rapid radial molten pool propagation within laser-heated metal leading to preferential generation of transverse acoustic waves from sources surrounding the molten mass resulting in the delay of shear wave transit times. Developed laser-based technique aims for applications involving remote examination of rapid melting processes of materials present in harsh environment (e.g. spent nuclear fuels) with high spatio-temporal resolution. © 2017 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). [http://dx.doi.org/10.1063/1.4993591

Laser thermoelastic generation in metals above the melt threshold

An approach is presented for calculating thermoelastic generation of ultrasound in a metal plate exposed to nanosecond pulsed laser heating, sufficient to cause melting but not ablation. Detailed consideration is given to the spatial and temporal profiles of the laser pulse, penetration of the laser beam into the sample, the appearance and subsequent growth and then contraction of the melt pool, and the time dependent thermal conduction in the melt and surrounding solid throughout. The excitation of the ultrasound takes place during and shortly after the laser pulse and occurs predominantly within the thermal diffusion length of a micron or so beneath the surface. It is shown how, because of this, the output of the thermal simulations can be expressed as axially symmetric transient radial and normal surface force distributions. The epicentral displacement response to these force distributions is obtained by two methods, the one based on the elastodynamic Green’s functions for plate geometry determined by the Cagniard generalized ray method and the other using a finite element numerical method. The two approaches are in very close agreement. Numerical simulations are reported on the epicentral displacement response of a 3.12mm thick tungsten plate irradiated with a 4 ns pulsed laser beam with Gaussian spatial profile, at intensities below and above the melt threshol

Functionalization of single-walled carbon nanotubes using isotropic plasma treatment: Resonant Raman spectroscopy study

Functionalization of single-walled carbon nanotubes sSWNTsd by isotropic plasma treatment was studied using resonant Raman spectroscopy. It was shown that plasma-induced functionalization results in the uniaxial isotropic constriction of the nanotubes but preserves their overall structural integrity. It was demonstrated that NH3 ·H2O and hexamethyldisiloxan plasmas yield various types of conductivity for semiconducting SWNTs

Functionalization of single-walled carbon nanotubes using isotropic plasma treatment: Resonant Raman spectroscopy study

Functionalization of single-walled carbon nanotubes sSWNTsd by isotropic plasma treatment was studied using resonant Raman spectroscopy. It was shown that plasma-induced functionalization results in the uniaxial isotropic constriction of the nanotubes but preserves their overall structural integrity. It was demonstrated that NH3 ·H2O and hexamethyldisiloxan plasmas yield various types of conductivity for semiconducting SWNTs

Optimization of Arrays of Gold Nanodisks for Plasmon-Mediated Brillouin Light Scattering

Distributions of electric fields in two-dimensional arrays of gold nanodisks on a Si3N4 membrane, with light incident through the membrane, are modeled with the aim of determining array geometries for effective plasmon-mediated Brillouin light scattering (“surface-enhanced Brillouin scattering”) from phonons or magnons in a specimen placed in contact with such an array. Particular attention is devoted to average intensities and higher-wavevector components of the fields in a plane 2 nm from the circular nanodisk/vacuum interface, which is anticipated to be in the vicinity of the surface of a specimen. For nanodisks with diameters of 50 nm, the average intensity near the circular nanodisk/vacuum interface increases as the angle of the incident light approaches the normal of the Si3N4 surface. At low angles of incidence relative to the Si3N4 normal, average intensities also increase with decreasing array spacing, primarily because of the corresponding changes in fractional coverage area of the gold. The highest average intensities (with near-normal incidence and 70 nm array periodicity) are found to be ∼3 times that of the incident light. More significantly, higher-wavevector components of the fields are found to have intensities comparable to the incident light. This finding provides evidence for the feasibility of using surface plasmons in nanodisk or nanoline arrays to mediate Brillouin scattering from phonons or magnons with wavelengths of a few tens of nanometers, which would extend the wavevector range of Brillouin-scattering metrology by an order of magnitud

Optimization of Arrays of Gold Nanodisks for Plasmon-Mediated Brillouin Light Scattering

Distributions of electric fields in two-dimensional arrays of gold nanodisks on a Si3N4 membrane, with light incident through the membrane, are modeled with the aim of determining array geometries for effective plasmon-mediated Brillouin light scattering (“surface-enhanced Brillouin scattering”) from phonons or magnons in a specimen placed in contact with such an array. Particular attention is devoted to average intensities and higher-wavevector components of the fields in a plane 2 nm from the circular nanodisk/vacuum interface, which is anticipated to be in the vicinity of the surface of a specimen. For nanodisks with diameters of 50 nm, the average intensity near the circular nanodisk/vacuum interface increases as the angle of the incident light approaches the normal of the Si3N4 surface. At low angles of incidence relative to the Si3N4 normal, average intensities also increase with decreasing array spacing, primarily because of the corresponding changes in fractional coverage area of the gold. The highest average intensities (with near-normal incidence and 70 nm array periodicity) are found to be ∼3 times that of the incident light. More significantly, higher-wavevector components of the fields are found to have intensities comparable to the incident light. This finding provides evidence for the feasibility of using surface plasmons in nanodisk or nanoline arrays to mediate Brillouin scattering from phonons or magnons with wavelengths of a few tens of nanometers, which would extend the wavevector range of Brillouin-scattering metrology by an order of magnitud