Hodgkinson, JaneMasiyano, DacksonTatam, Ralph P.2011-09-082011-09-082009-01-01Jane Hodgkinson, Dackson Masiyano, and Ralph P. Tatam. Using integrating spheres as absorption cells: path-length distribution and application of Beer's law. Applied Optics, Vol. 48, 2009, Issue 30, pp. 5748-57580003-6935http://dx.doi.org/10.1364/AO.48.005748http://dspace.lib.cranfield.ac.uk/handle/1826/4298We have modeled the path-length distribution in an integrating sphere used as a multipass optical cell for absorption measurements. The measured radiant flux as a function of analyte concentration is nonlinear as a result, deviating from that expected for a single path length. We have developed a full numerical model and introduce a new analytical relationship that describes this behavior for high reflectivity spheres. We have tested both models by measuring the optical absorption of methane at 1651nm in a 50mm diameter sphere, with good agreement with experimental data in the absorption range 0-0.01cm -1 . Our results compare well with previous work on the temporal response of integrating spheres.en-UKArticle