Looking into Skin and Artwork – Applications of Nonlinear Optical Microscopy in Biomedicine and Cultural Heritage

19.07.2018, 14:00

Prof. Martin Fischer, Duke University, Durham, USA

Nonlinear optical microscopy can provide contrast in highly heterogeneous media and a wide range of applications has emerged, primarily in biology, medicine, and materials science. The localized nature of nonlinear interactions leads to high spatial resolution, optical sectioning, and large possible imaging depth in scattering media. However, nonlinear contrast (other than fluorescence, harmonic generation or CARS) is generally difficult to measure because it is overwhelmed by the large background of detected illumination light. This background can be suppressed by using tailored femtosecond pulses or pulse trains to encode nonlinear interactions in background-free regions of the frequency spectrum.

While this technology was initially applied to study optical properties of solid-state materials, advancements in laser and detector hardware have allowed us to develop a microscope that can access a wide range of nonlinear optical contrast at high spatial resolution with power levels that are safe to use on biological samples. With this pump-probe microscope, we have been able to measure detailed transient absorption dynamics of melanin sub-types in a variety of skin lesions, showing sensitivity to metastatic potential of the disease. More recently, we have applied this technology to paint samples and historic artworks in order to provide high-resolution, depth-resolved images of pigments and their degradation products. However, the limited tuning range of our solid state laser system restricts the range of accessible pigments. I will discuss the principle of this microscopy technique, review recent applications in materials science, biomedicine and art conservation, and describe plans to extend the applicability of pump-probe microscopy using optical fiber sources.