Nonlinear optical spectroscopy and two-photon excited fluorescence spectroscopy reveal the excited states of fluorophores embedded in a beetle's elytra

Sébastien R Mouchet, Charlotte Verstraete, Dimitrije Mara, Stijn Van Cleuvenbergen, Ewan D Finlayson, Rik Van Deun, Olivier Deparis, Thierry Verbiest, Bjorn Maes, Pete Vukusic, Branko Kolaric

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Upon illumination by ultraviolet light, many animal species emit light through fluorescence processes arising from fluorophores embedded within their biological tissues. Fluorescence studies in living organisms are however relatively scarce and so far limited to the linear regime. Multiphoton excitation fluorescence analyses as well as nonlinear optical techniques offer unique possibilities to investigate the effects of the local environment on the excited states of fluorophores. Herein, these techniques are applied for the first time to study of the naturally controlled fluorescence in insects. The case of the male Hoplia coerulea beetle is investigated because the scales covering the beetle's elytra are known to possess an internal photonic structure with embedded fluorophores, which controls both the beetle's coloration and the fluorescence emission. An intense two-photon excitation fluorescence signal is observed, the intensity of which changes upon contact with water. A third-harmonic generation signal is also detected, the intensity of which depends on the light polarization state. The analysis of these nonlinear optical and fluorescent responses unveils the multi-excited states character of the fluorophore molecules embedded in the beetle's elytra. The role of form anisotropy in the photonic structure, which causes additional tailoring of the beetle's optical responses, is demonstrated by circularly polarized light and nonlinear optical measurements.

Original languageEnglish
Article number20180052
Pages (from-to)20180052
Number of pages8
JournalInterface focus
Issue number1
Publication statusPublished - 6 Feb 2019


  • natural photonics
  • photonics crystals
  • fluorescence
  • two-photon fluorescence
  • third-harmonic generation
  • Beetle
  • Natural photonics
  • Third-harmonic generation
  • Photonic crystals
  • Fluorescence
  • Two-photon fluorescence

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  • Projects


    • 1 Participation in conference
    • 1 Oral presentation

    Linear and Non-Linear Fluorescence Investigation of a Beetle’s Photonic Structure

    Sébastien Mouchet (Speaker)

    17 May 2017

    Activity: Talk or presentation typesOral presentation

    Belgian Physical Society (BPS) General Scientific Meeting 2017

    Sébastien Mouchet (Poster)

    17 May 2017

    Activity: Participating in or organising an event typesParticipation in conference

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