Concentration-modulated absorption spectroscopy and the triplet state: Saturation effects in long-lived triplets

W. Jeremy Jones, Christopher Shaw, Daniel Thomas, András Grofcsik, Miklós Kubinyi

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The theory and technique of the pump and probe method of Concentration Modulated Absorption Spectroscopy (COMAS) has been extended to species with high triplet yields. In the experiments crythrosin B and rose bengal have been applied as model compounds. Using continuous wave laser sources and a modulated pump beam the large COMAS signal expected from the formation of long-lived triplets is shown to be dramatically reduced as a result of strong saturation effects. A gain expression is derived which takes into account such saturation effects and which describes satisfactorily the interaction of coinciding focused Gaussian pump and probe beams with the sample solution. Based on this theory, singlet and triplet concentration profiles in the focal region in the sample can also be evaluated. Such a treatment will be of value in modelling the refractive index gradients that arise from the differing molecular polarisabilities of singlet and triplet molecular species and from the energy conversion of electronic excitation to heat.

Original languageEnglish
Pages (from-to)93-109
Number of pages17
JournalPeriodica Polytechnica Chemical Engineering
Issue number2
Publication statusPublished - Jan 1 2001



  • Photoinduced absorption/bleaching
  • Triplet
  • Xanthene dyes

ASJC Scopus subject areas

  • Chemical Engineering(all)

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