This paper describes a multipass absorption sensor based on an integrating sphere. The sphere has an internal coating
which is highly reflective (over 95%) in the near infrared region and this allows the detection of carbon dioxide (CO<sub>2</sub>)
gas at 2 &mgr;m. CO<sub>2</sub> was detected using a light emitting diode as the emitter and a photodiode as the detector. A two inch
(50.8 mm) diameter integrating sphere was used as an absorption gas cell. A method of calculating the effective path
length of the integrating sphere is also presented. The latter is shown to be dependant on the reflectance of the sphere's
internal surface, the sphere's port fraction and the level of attenuation of the optical signal due to the gas present in the
sphere. Effective optical path lengths of 40 cm at the 2 &mgr;m region are reported. Experimental results demonstrating the
detection of CO<sub>2</sub> using a two inch diameter integrating sphere are presented and these are compared to simulation results
based on a CO<sub>2</sub> absorption over a 40 cm path length at 2 &mgr;m.
The reduction of harmful environmental pollutants which can have adverse effects on human health and the development of sensors capable of monitoring low concentrations of these pollutants is a major source of concern for many researchers today. This paper describes a multipass absorption cell used to detect and monitor the presence of several gases in the ultra violet and visible regions. An integrating sphere with a highly reflective internal coating (over 99%) was adapted in order to input and output various gases. Sulphur dioxide was detected in the ultra violet region, ozone in the visible and nitrogen dioxide in both the ultra violet and visible. This paper will report the generation of effective optical path lengths of up to 70 cm using a 5 cm diameter integrating sphere. This results in an optical sensor capable of detecting sulphur dioxide concentrations as low as 10 ppm, nitrogen dioxide concentrations as low as 4 ppm and ozone levels of the order of 500 ppm.
This paper describes two optical based sensors for the detection and quantification of vehicle exhaust pollutants. The first sensor consists of a single pass absorption cell. Broadband light from a deuterium/halogen source was transmitted through the cell from optical fibre and the resulting absorption is detected using a UV spectrometer which was also fibre coupled. The second approach includes an integrating sphere, which has been adapted for use as a multipass absorption cell. An ultraviolet LED was used as an emitter and a photodiode as the detector. Both were mounted directly on the sphere. The single pass absorption cell has been used to monitor nitric oxide, nitrogen dioxide and sulphur dioxide while the integrating sphere has been used to monitor nitrogen dioxide levels. Concentration levels of 10's of parts per million have been measured for each gas and sensor.