Determination of the absolute two-photon absorption cross section of tryptophan

P. Sengupta, J. Balaji, S. Mukherjee, R. Philip, G. R. Kumar, S. Maiti

Research output: Contribution to journalConference articlepeer-review


Two-photon excitation can excite physiological ultraviolet (UV) chromophores at visible wavelengths and holds significance for applications such as non-linear microscopy, micro-pharmacology, localized heating and tissue ablation. However, little quantitative data is available on the absolute two-photon absorption cross sections (σ2) of these molecules. Their low two-photon absorbance and limited solubility implies that the sensitivity required for such measurements is much higher than that available from standard techniques. We employ the recently developed generalized z-scan technique to measure the absolute value of the σ2 of tryptophan, the most ubiquitous of the physiological near-UV chromophores, and obtain the value of 32.0 ± 1.2 mGM (1 GM = 10-50 cm4sec/photon/molecule) at 532 nm. This is the first determination of the absolute σ2 of any biological UV chromophore, and can be used to calibrate the previously reported relative two-photon excitation spectra of a number of such molecules.

Original languageEnglish (US)
Pages (from-to)336-339
Number of pages4
JournalProceedings of SPIE - The International Society for Optical Engineering
StatePublished - 2001
Externally publishedYes
EventMultiphoton Microscopy in the Biomedical Sciences - San Jose, CA, United States
Duration: Jan 21 2001Jan 23 2001

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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