Summary of Research Interests
My research concerns laser spectroscopy and its use in analytical chemistry and in studies of gas phase kinetics and dynamics. The research is characterised by novel technique and instrument development which not only allows innovative fundamental studies of chemical dynamics and photon science but that can also be translated into the real world. Particular areas of interest are healthcare and medicine, plasmas diagnostics and atmospheric chemistry.
Laser absorption spectroscopy and its applications
Most of our work uses different forms of cavity enhanced laser absorption spectroscopies such as (off-axis) cavity enhanced absorption spectroscopy (CEAS), cavity ringdown spectroscopy (CRDS) and optical feedback cavity enhanced absorption spectroscopy (OF-CEAS) to make measurments of the absolute concentrations of trace species. We employ diode lasers, sum and difference frequency generation methods, and both quantum and interband cascade lasers (QCLs/ICLs) as radiation sources.
(i) Healthcare and Medicine
Our group, in collaboration with Prof. Peter Robbins (DPAG), has developed a novel fast real-time breath sensor. The analyser, termed a molecular flux sensor (MFS), uses diode laser absorption within an optical cavity in combination with a state-of-the art flow meter and is capable of measuring lung inhomogeneity. As an example the figure belows shows data from measurements on 6 healthy young participants, 6 healthy older participants, and 6 patients with chronic obstructive pulmonary disorder (COPD). The top panel of the figure shows the distributions for standardised compliance, CL*, and conductance, Cd*, for each participant group and there is a clear increase in the width of the distributions for the COPD group. Furthermore, the distribution of deadspace is markedly larger for COPD patients (lower panel). The returned parameter values are highly repeatable from test-to-test indicating the potential of such measurements for stratifying lung disease. Ongoing studies include studies on subjects with asthma, cystic fibrosis and COPD.
(ii) Plasma diagnostics
Quantitative measurements of the concentrations of trace gas species in plasmas are vital for understanding and directing research in this applied area. Diode lasers in combination with modulation spectroscopies and/or cavity enhanced methods are sensitive enough to measure physico-chemical properties such as the absolute number densities, translational, internal temperatures, field effects and the electron energy distribution as a function of the plasma operating conditions. Of partciular interest are cold atmospheric pressure plasma (CAPs) which are a source of reactive oxygen and nitrogen species, RONS, many of which are also produced naturally in cells and can regulate cellular and physiological processes. As such CAPs are finding an increasing number of medical applications and when applied to living tissue, they can destroy, or at least significantly reduce the size of, cancerous tumours. Ongoing research seeks to quantify the fluxes of selected primary and secondary RONS with a view to improving our understanding of plasma medicine.
(iii) Atmospheric chemistry
Many trace species play important roles in key processes that determine the equilibrium and composition of the atmosphere, OH for example (whose concentration is typically sub-parts per trillion) essentially controls the daytime oxidative capacity of the atmosphere. In order to fully understand the chemistry occurring in our atmosphere it is necessary to be able to measure the concentrations of these trace species both accurately and quickly. Cavity enhanced spectroscopies provide a robust, sensitive and accurate method for making quantitative measurements of such species in both clean and polluted atmospheres. On Ongoing research is focussing upon developing methods to detect peroxy radicals.
Selected Recent publications
- Potential for non-invasive assessment of lung inhomogeneity using highly precise, highly time-resolved, measurements of gas exchange. J.E. Mountain, P. Santer, D.P. O’Neill, N.M.J. Smith, L. Ciaffoni, J.H. Couper, G.A.D. Ritchie, G. Hancock, J.P. Whiteley, P.A. Robbins, Journal of Applied Physiology 124 615 (2018).
- Broadening the optical bandwidth of quantum cascade lasers using RF noise current perturbations T.H. Pinto, J.M.R. Kirkbride, G.A.D. Ritchie, Opt. Lett. 321041 March (2018).
- Intercomparison of HO2 measurements by Fluorescence Assay by Gas Expansion and Cavity Ring–Down Spectroscopy within HIRAC. L. Onel, A. Brennan, M. Gianella, G. Ronnie, A. Lawry-Aguila, G. Hancock, L. Whalley, P.W. Seakins, G.A.D. Ritchie, D.E. Heard, Atmos. Meas. Tech. 10 4877 (2017).
- Intracavity Faraday Modulation Spectroscopy (INFAMOS): a tool for radical detection. M. Gianella, T.H. Pinto, X. Wu, G.A.D. Ritchie, J. Chem. Phys. 147 054201 (2017).
- ICL based OF-CEAS: a sensitive tool for analytical chemistry. K.M. Manfred, K.E. Hunter, L. Ciaffoni, G.A.D. Ritchie, Analytical Chemistry, 89 902 (2017).
- Detection of HO2 in an atmospheric pressure plasma jet using optical feedback cavity-enhanced absorption spectroscopy. M. Gianella, S. Reuter, A. Lawry Aguila, J.H. van Helden, G.A.D. Ritchie, New Journal of Physics 18 113027 (2016).
- In-airway molecular flow sensing: A new technology for continuous, non-invasive monitoring of oxygen consumption in critical care. L. Ciaffoni, D.P. O’Neill, J.H. Couper, G.A.D. Ritchie, G. Hancock, P.A. Robbins Science Advances 2 8 e1600560 (2016)