Fluorescence spectrometry photon counting

It has become common practice in x-ray fluorescence spectrometry to use the word intensity and the symbol I when referring to the photon counting rate at the detector. Based on the strict classical definition of intensity [48] this is a misuse of the term. On the other hand, the word intensity is so convenient when used to mean counting rate, that the looser use can be expected to persist. Therefore, it becomes important for the spectroscopist to understand and avoid the confusion that can arise from the dual use of the term. 

Fluorescence is excited by laser (e.g. argon), and the back-scattered fluorescent light picked up by the fibre and analysed by spectrometry and photon-counting techniques. Where a single fibre is used to carry both the exciting and fluorescent light, the natural fluorescence in the fibre can limit the lower detection limit (3 x 10 ) for Rhodamine B dye detected by a 600/im polymer-clad silica fibre (33). This can be overcome using two separate fibres. 

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