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Open Access research with a European policy impact...

The Strathprints institutional repository is a digital archive of University of Strathclyde's Open Access research outputs. Strathprints provides access to thousands of Open Access research papers by Strathclyde researchers, including by researchers from the European Policies Research Centre (EPRC).

EPRC is a leading institute in Europe for comparative research on public policy, with a particular focus on regional development policies. Spanning 30 European countries, EPRC research programmes have a strong emphasis on applied research and knowledge exchange, including the provision of policy advice to EU institutions and national and sub-national government authorities throughout Europe.

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Tunable diode laser spectroscopy with wavelength modulation : elimination of residual amplitude modulation in a phasor decomposition approach

Ruxton, Keith C. and Chakraborty, Arup Lal and Johnstone, W. and Lengden, Michael and Stewart, G. and Duffin, K. (2010) Tunable diode laser spectroscopy with wavelength modulation : elimination of residual amplitude modulation in a phasor decomposition approach. Sensors and Actuators B: Chemical, 150 (1). pp. 367-375. ISSN 0925-4005

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Recovery and analysis of the first harmonic signals in tunable diode laser spectroscopy (TDLS) with wavelength modulation (WM) are limited by the presence of a high background signal upon which the small gas signals are superimposed. This high background signal is a result of direct modulation of the source laser power and is referred to as the residual amplitude modulation (RAM) signal. This paper presents further details of a recently reported technique to optically remove the RAMand an analytical model that enables the use of the phasor decomposition (PD) method with it to extract the absolute gas absorption line-shape from the recovered first harmonic signals. The PD method is important as it provides a calibration-free technique for gas concentrationmeasurements. A major benefit of RAM nulling is that signal amplification can be increased without equipment saturation due to the background RAM, resulting in improved signal resolution and system sensitivity. A comparison of experimental measurements of the 1650.96 nm absorption line of methane (CH4) with line-shapes derived from HITRAN data illustrates and validates the use of the PD method with the new RAMnulling procedure. This advancement is useful for industrial applications where stand-alone and calibration-free instrumentation is required.