Fluctuation in nano- and micro-imaging
In the advanced optical technologies, the fluctuation in the system may cause fatal errors in the measurement of extremely weak signals, degrading the accuracy and resolution of imaging and fabrication. Advanced nano-instruments such as atomic force microscopes and advanced enhanced Raman scattering microscopes, have used extremely low-noise detectors and low-noise electronic circuits. To suppress the fluctuation, experiments were made on the vibration-isolated optical tables in dark and clean rooms. Ultra-high vacuum and cryogenic technologies are also used, while samples are not alive in such an environment. In this presentation, I will talk about nano- and micro-imaging with fluctuation, where the fluctuation is rather the source of nano-imaging, but not that of the error and noise. For nano-Raman imaging of a live cell, fluctuation has been used for moving a plasmonic nanoparticle in a cell [Nano Lett. 11, 5344 (2011)]. In the method, a gold nano-particle endocytosed into a cell fluctuates randomly in the cell, and meets local molecules. A molecular map is drawn by measuring Raman scattering signals of molecules near the particle, simultaneously by detecting the trajectory of particle with a dark-field super-resolution microscope. This concept has been applied to conventional laser-scanning confocal microscopy. Rather than conventional raster scanning, a laser-beam spot fluctuates as a random walk, based on a stochastic process [J. Jpn. Soc. Precis. Eng. 87, 740 (2021)]. The method drastically reduces the experimental time, typically by a factor of five to ten. Fluctuation has been also used for the nano-fabrication of large-scale structures. If time allows, I will talk about our work on the self-fabrication of metamaterials grown in the fluctuation [APL Photonics 1, 050801 (2016)].