Abstract
We present an image-based autofocusing system applied in nonlinear microscopy and spectroscopy with a wide range of excitation wavelengths. The core of the developed autofocusing system consists of an adapted two-step procedure maximizing an image score with six different image scorings algorithms implemented to cover different types of focusing scenarios in automated regime for broad wavelength region. The developed approach is combined with an automated multi-axis alignment procedure. We demonstrate the key abilities of the autofocusing procedure on different types of structures: single nanoparticles, nanowires and complex 3D nanostructures. Based on these experiments, we determine the optimal autofocusing algorithms for different types of structures and applications.
Highlights
Modern optical microscopy techniques include big varieties of physical principles to characterize structures with resolutions ranging from hundreds of microns to tens of nanometers [1]
We present an image-based autofocusing system applied in nonlinear microscopy and spectroscopy with a wide range of excitation wavelengths
When the excitation laser beam is focusing in a medium, high intensities induce a nonlinear polarization response with respect to the electric field. This leads to multiple photon processes including multiphoton absorption, sum frequency generation (SFG), second harmonic generation (SHG), and third harmonic generation (THG) etc [3,4,5,6]
Summary
Modern optical microscopy techniques include big varieties of physical principles to characterize structures with resolutions ranging from hundreds of microns to tens of nanometers [1]. These systems do not allow to autofocus in a broad range of the laser excitation and collection wavelengths That limits their application for nonlinear optical microscopy, especially in the fields of material analysis and nonlinear photonics structures characterization. We present an image-based autofocusing system developed for highresolution nonlinear optical microscopes This system allows in a fully automated regime to characterize the nonlinear optical responses while sweeping the excitation laser wavelength, polarization power and position of the sample. In our work we combined one strategy to maximize the focus score with the methods of multiphoton imaging microscopy This approach allows to perform in a fast and reliable manner the nonlinear optical characterizations in a fully automated regime without any limitations to a specific wavelength region. The developed method can significantly reduce the duration measurements’ time and increase the quality as well as the reproducibility of the nonlinear optical characterizations in material science and other nonlinear photonics research areas
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