Robert Randolph

Dual-colour single-shot coherent Rayleigh scattering (CRS) is utilised to simultaneously measure the temperature and relative number density in a weakly ionised DC glow discharge. The discharge is produced using xenon gas at a pressure of 15 Torr. By analysing the lineshapes, both the translational temperature and relative number density of neutral xenon atoms are obtained. Measurements at the centre of the discharge are obtained as a function of discharge current. Additionally, spatially resolved measurements are performed across the discharge at an operating discharge current of 15 mA. The spatial results are compared with a one-dimensional radial fluid model of neutral gas flow informed by a 0D plasma global model of the glow discharge. The comparison shows good agreement, demonstrating the capability of CRS toward diagnostics for weakly ionised, low temperature plasmas.

We demonstrate neutral gas-flow velocimetry by exploiting the optical dipole forces exerted by precisely tailored high-intensity laser fields on polarizable particles, in the form of single-shot coherent Rayleigh-Brillouin scattering (CRBS). This enables mapping of the velocity distribution function of the particles in a single laser shot of approximately 200 ns duration, allowing us to perform spectroscopic measurements in the time, rather than the frequency, domain. Importantly, CRBS results in a coherent signal beam, which renders the technique ideal for measurements in optically noisy environments. By correlating the time shift of the resulting spectrum to the Doppler shift caused by the bulk motion of particles, we perform neutral gas-flow velocimetry without the need to seed the flow, nondestructively, for a variety of gases, atomic or molecular. We demonstrate gas-flow velocimetry at flow velocities as low as 1 m s − 1 , with similar velocity resolution, while temperature and gas density can also be estimated from the same single-shot spectra. To prove the effectiveness of the measurement technique, we benchmark it against Pitot tube measurements, which show excellent agreement.

This article presents an experimental demonstration of a spectroscopic method based on the dispersion of the scattering spectrum from laser-illuminated liquid water collected through a rubidium atomic vapor prism cell. Resonant absorption at 780 nm suppresses Mie/Rayleigh scattering and the steep gradients in refractive index near the 780 nm absorption lines separate Brillouin scattering from Raman scattering in liquid water. The opposing spatial displacements of the Stokes and Anti-Stokes shifted Brillouin peaks yield a measurement of their spectral shifts and thus the temperature or salinity of the water. Performance of the prism cell was mapped with a frequency tunable laser for frequency offsets from the center of the rubidium absorption feature of between −15 GHz and 15 GHz and at rubidium cell temperatures between 148 °C and 177 °C. The experimental results are compared with a numerical model and show good agreement with the scattering peak displacements within experimental uncertainties of probe frequency and cell temperature. In the present configuration, the minimum detectable frequency shift is estimated to be 15.5 MHz. Experiments were conducted in water demonstrating the utility of this method for the measurement of water temperature. Liquid water LiDAR was suggested as one of the possible applications for this method and several ways to improve the experimental setup and cell temperature stability were identified.

A two order of magnitude spectral acquisition improvement in velocity distribution function measurement is demonstrated with a novel single-shot, dual-color coherent Rayleigh–Brillouin scattering (CRBS) scheme. By performing this non-resonant and seedless spectral diagnostic technique, capable of obtaining a spectrum in ∼ 300 ns, we demonstrate accurate temperature (ranging from 300 K to 500 K) and pressure (ranging from 760 Torr down to 1 Torr) measurement capabilities, for a variety of atomic, molecular and multispecies gases. This demonstrated gas thermodynamic characterization capability of the dual-color CRBS scheme over broad ranges of pressure and temperature for a variety of gases is anticipated to be of great interest to a plethora of fields, ranging from aerospace applications to low-temperature plasmas, providing with an accurate measurement of physical properties of neutral particles, for a range of gases.

This work presents the first, to the best of our knowledge, experimental demonstration of slow light imaging spectroscopy for thermometry of liquid water. This novel technique for measuring temperature relies on detecting the spectral shift of Brillouin peaks in water using the temporal delay through a cell containing an atomic vapor. Stand-off sensing capabilities are achieved by time-domain measurements of Brillouin scattering tuned to be near a rubidium atomic resonance and passed through a cell filled with rubidium vapor. An injection seeded optical parametric oscillator (OPO) is demonstrated to be a versatile light source for slow light imaging spectroscopy applications. The narrow OPO pulse spectrum allows for a precise profiling of slow light features of rubidium and accurate tracking of the temperature dependence of Brillouin scattering spectral shift. A comparison between the experimental data and numerical simulation over a temperature range of 20 to 99 degrees Celsius shows a good agreement for both qualitative and quantitative results.

A dual color, frequency and pulse duration agile laser system, capable of delivering laser pulses in arbitrary temporal profiles with ∼1 ns to ∼1 µs pulse duration, chirping rates of ∼27 MHz/ns with an achievable chirping range of several GHz across the pulse duration, and with energies ranging from a few nJ to hundreds of mJ per pulse has been developed. The flexibility and capability of this laser system provide a wide range of laser parameters that can be exploited to optimize operational conditions in various experiments ranging from laser diagnostics to spectroscopy and optical manipulation of matter. The developed system is successfully demonstrated to obtain coherent Rayleigh-Brillouin scattering (CRBS) in both single and dual color configuration, in an effort to expand the non-intrusive accessibility towards lower pressure regime for neutral gas and plasma diagnostics.

This letter presents an experimental study and the associated numerical modeling of fast-curing, thermosetting droplets spreading on a heated surface. The results show a significant morphological dependence of the spreading droplets of Ecoflex 0050 (a heat-sensitive, platinum-catalyzed silicone material) on thermal conditions. Differential scanning calorimetry and rheometry provide quantifiable data for modeling the cure kinetics and rheological properties of the material. This work demonstrates an approach to developing a phenomenological model suitable for predicting the morphological variation of fast-curing, thermosetting materials without prior knowledge of their chemical composition. The developed multiphysics models for cure kinetics and chemorheology can serve as a functional tool for predictions requiring accurate dimensional control of free-forming thermosetting materials, such as nozzle-based additive manufacturing, centrifugal coating and forming, fabrication of soft robots, and soft lithography.