ABSTRACT
We demonstrate the quantitative capabilities of Raman confocal microscopy as a nondestructive method to measure the partial pressure of molecular gases in mm3 range sealed volume having an optical access. Thanks to a calibration procedure, we apply this technique for the characterization of the absolute nitrogen partial pressure inside buffered micro electromechanical system (MEMS) atomic vapor cells developed for atomic clocks. Our results are compared with measurements obtained by rubidium hyperfine frequency spectroscopy and a good agreement is demonstrated between the two methods, with a three-sigma detection limit below 10 mbar for a 1 h integration time, using a 33 mW 532 nm excitation laser. These results prove the potential of confocal micro-Raman spectroscopy as a simple and nondestructive method for small-scale pressure measurements.
ABSTRACT
Raman spectroscopy is the workhorse for label-free analysis of molecules. It relies on the inelastic scattering of incoming monochromatic light impinging molecules of interest. This effect leads to a very weak emission of light spectrum that provides a signature of the molecules being observed. Considerable efforts have been made over the last decades, in particular with the development of Surface Enhanced Raman Spectroscopy (SERS), to enhance the intensity of the emitted signal so that ultimately, traces of molecules can be detected. Here, we show that dense self-organized networks of quasi-monodisperse nanoparticles redepositing during femtosecond laser ablation of trenches in fused silica can lead to a significant field enhancement effect, enabling the Raman detection of a single-molecule layer deposited on the surface (so called monolayer). Unlike previously reported for SERS experiments, here, there is no metal layer promoting plasmonics effects causing localized field enhancement. The method for producing SERS substrates is therefore quite straightforward and low cost.
ABSTRACT
Micro-fabricated (MEMS) alkali vapor cells are at the heart of the miniaturization of atomic devices such as atomic magnetometers, atomic gyroscopes and atomic clocks. Among the different techniques used to fill microfabricated alkali vapor cell, UV decomposition of rubidium azide (RbN3) into metallic Rb and nitrogen in Al2O3 coated cells is a very promising approach for low-cost wafer-level fabrication. Here we present a detailed lifetime study of such cells. The rubidium consumption being the main identified cell failure mode, it is monitored with an novel image analysis technique and with high temperature long term aging tests.
ABSTRACT
The efficacy of an electrochemical treatment in water disinfection, using boron-doped diamond electrodes, was studied and its suitability for the fresh-cut produce industry analyzed. Tap water (TW), and tap water supplemented with NaCl (NaClW) containing different levels of organic matter (Chemical Oxygen Demand (COD) around 60, 300, 550 ± 50 and 750 ± 50 mg/L) obtained from lettuce, were inoculated with a cocktail of Escherichia coli O157:H7 at 105 cfu/mL. Changes in levels of E. coli O157:H7, free, combined and total chlorine, pH, oxidation-reduction potential, COD and temperature were monitored during the treatments. In NaClW, free chlorine was produced more rapidly than in TW and, as a consequence, reductions of 5 log units of E. coli O157:H7 were achieved faster (0.17, 4, 15 and 24 min for water with 60, 300, 500 and 750 mg/L of COD, respectively) than in TW alone (0.9, 25, 60 min and 90 min for water with 60, 300, 600 and 800 mg/L of COD, respectively). Nonetheless, the equipment showed potential for water disinfection and organic matter reduction even without adding NaCl. Additionally, different mathematical models were assessed to account for microbial inactivation curves obtained from the electrochemical treatments.
