Publications

A preliminary investigation of the use of supercritical carbon dioxide for treating of 3M 1860 N95 masks was undertaken to evaluate a potential route to low-cost, scalable, sterilization of personal protective equipment for multiple reuse in hospital settings. Upon entering the supercritical regime, the normally distinct liquid and gaseous phases of CO₂ merge into a single homogeneous phase that has density, short-range order, and solvation capacity of a liquid, but the volume-filling and permeation properties that of a gas. This enables supercritical CO2 to function as a vehicle for delivery of biocidal agents such peracetic acid into microporous structures. The potentially adverse effect of a liquid-to-gas phase transition on mask filter media is avoided by conducting cleaning operations above 31 C, the critical temperature for carbon dioxide. A sample of fifteen 3M 1860 N95 masks was subjected to ten consecutive cycles of supercritical CO₂ cleaning to determine its effect on mask performance. These 15 masks, along with 5 control samples then underwent a battery of standardized tests at the CDC NIOSH NPPTL research facility in Pittsburgh, PA. The data from these tests strongly suggest (but do not prove) that supercritical carbon dioxide do not damage 3M 1860 N95 masks. Additional tests conducted during this project confirmed the compatibility of supercritical CO₂ with ventilator tubing that, like N95 masks, has been in short supply during portions of the COVID-19 pandemic and cannot be sterilized by conventional means. Finally, a control experiment was also conducted to examine the effect of supercritical CO₂ on a BSL-2 surrogate virus, vesicular stomatitis virus (VSV), Indiana serotype strain. In the absence of biocidal additives, supercritical CO₂ exhibited no measurable lethality against VSV. This surrogate virus experiment suggests that a biocidal additive such as peracetic acid will be necessary to achieve required sterilization metrics.

Recent advances in power scaling of Yb+ 3-doped fiber lasers to the kilowatt level suggest a need to examine the performance of Yb + 3-doped silica at temperatures well above ambient. We report experimental results for the absorption coefficient, emission cross-section, fluorescence lifetime, and slope efficiency of a Yb3+-doped large mode area (LMA) silica fiber for temperatures spanning 23 °C-977 °C. To the best of our knowledge these are the highest temperatures to date for which these optical properties have been measured. We find a sharp reduction in the energy storing capability and lasing performance of Yb+ 3:SiO 2 above 500 °C that coincides with the onset of non-radiative transitions in the excited state manifold (thermal quenching). As the temperature increases from room temperature to 977 °C, absorption in the 1020-1120 nm operating band increases monotonically, concurrent with a reduction in absorption at the 920-nm and 977-nm pumping bands. Conversely, the spectral weight of the emission cross-section shifts from transitions above 1010 nm to those below, with the exception of the 977-nm emission band. © 2011 Elsevier B.V. All rights reserved. © 2011 Elsevier B.V. All rights reserved.