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Nonlinear biophotonics

Academic lead: Professor Julian Moger

Biophotonics lies at the interface between Biology and Photonics and deals with the interaction between light and biological materials. Nonlinear Biophotonics concerns the special case of optical processes where the response scales nonlinearly with incident light intensity. Compared to conventional (linear) optics, nonlinear processes offer many advantages for probing biological systems; the near-IR excitation extends the depth penetration into tissues with minimal photodamage and the nonlinear signal dependence provides intrinsic 3D optical sectioning. Moreover, utilizing the intrinsic nonlinear optical responses of selected biomolecules, it is possible to derive label-free biochemical contrast of living tissues.

Optical nonlinearities are typically only observed at extremely high light intensities that correspond to average powers that prohibit their use for non-invasive bio-imaging. However, by using ultra-short laser pulses sufficiently high peak intensities can be achieved with tolerable average optical powers. Pulse widths in the range of 100 fs – 10 ps and repetition rates ~100MHz are typically used for biological applications. Excitation in the near-infrared is optimal since the longer excitation wavelength affords deeper penetration into scattering tissues and the low photon energy reduces (linear) photodamage.

We have state-of-the-art nonlinear imaging and spectroscopy facilities, which are strongly supported by staff with expertise in the development and application of nonlinear optics. Fundamental research in our laboratory is supported by the Research Councils and Medical Research charities is successfully being translated into commercial applications through close partnership with industry.

Nonlinear Optical Techniques

The list of Nonlinear Optical processes that can be used for biological applications is ever growing. At Exeter we currently use the following modalities to derive label-free chemically specific image contrast:

  • Multiphoton Fluorescence (MPF)
  • Second Harmonic Generation (SHG)
  • Four Wave Mixing (FWM)
  • Coherent Raman Scattering (CARS and SRS)
  • Nonlinear Photothermal Lensing (NPL)
  • Two Photon Absorption (TPA)

Applications of Nonlinear Biophotonics

Nonlinear microscopy can be applied to a wide range of biomedical applications. At Exeter we have expertise in the following applications of nonlinear microscopy.

  • Live Cell Imaging
  • Membrane Biophysics
  • Extracellular matrix: structure, micromechanics and permeability
  • Plant Imaging
  • Microvascular Biophysics
  • Cancer Research
  • Bio-Nanomaterials
  • Graphene Research