The detection and measurement of gas concentrations using the characteristic optical absorption of the gas species is important for both understanding and monitoring a variety of phenomena from industrial processes to environmental change. This article reviews the field, covering several individual gas detection techniques including non-dispersive infrared (NDIR), spectrophotometry, tunable diode laser spectroscopy and photoacoustic spectroscopy. We present the basis for each technique, recent developments in methods and performance limitations. The technology available to support this field, in terms of key components such as light sources and gas cells, has advanced rapidly in recent years and we discuss these new developments. Finally, we present a performance comparison of different techniques, taking data reported over the preceding decade, and draw conclusions from this benchmarking.

We develop a simple temperature sensing using an optical time domain reflectometer (OTDR) and a mechanical long-period fiber grating (LPFG) fabricated from a heat-shrinkable tube and a metric screw. The resonance loss of the fabricated LPFG is strongly dependent on temperature as temperature-dependent heat-shrinkage of the tube produces a change in the pressure applied to the fiber. In our proposed temperature sensor, the LPFG insertion loss due to a change in the pressure applied to the fiber is measured using an OTDR with a resonance wavelength. Both single-point and multi-point temperature sensing is successfully demonstrated experimentally. "Bend-insensitive ultra short long-period gratings by the electric arc method and their applications to harsh environment sensing and communication ," "High-temperature stability of long-period fibre gratings using an electric arc,"

An overlay material was deposited by the Langmuir-Blodgett technique onto a single-mode optical fiber containing a long-period grating. The long-period grating exhibits characteristic attenuation bands in its transmission spectrum whose central wavelengths were observed to depend on the optical thickness of the overlay material, even for materials that have a refractive index higher than that of silica.

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Shearography is a full-field speckle interferometric technique used to determine surface displacement derivatives. For an interferometric technique, shearography is particularly resilient to environmental disturbances and has hence become an invaluable measurement tool outside of the optics laboratory. Furthermore, the inclusion of additional measurement channels has turned shearography from a qualitative inspection tool into a system suitable for quantitative surface strain measurement. In this review article we present a comprehensive overview of the technique, describing the principle of operation, optical configurations, image processing algorithms and applications, with a focus on more recent technological advances.