Near-infrared non-contact microsphere microscope for contrast-enhanced optical nano-imaging.

Suffering from the background light scattering, the imaging contrast of a microsphere microscope is relatively low. In this paper, a near-infrared (NIR) microsphere microscope is proposed to enhance the imaging contrast. The imaging contrast is evaluated using different objective lenses at different microsphere diameters. The utilization of microspheres enhances the resolution of NIR objectives, enabling the distinction of structures with ∼220nm gaps. A far-field intensity distribution simulation is used to explain the reduced off-axis scattering under NIR illumination, and a modified refractive index theory considering the wave-optics effects in microspheres is utilized to analyze the NIR imaging performance. The proposed NIR microsphere microscope significantly improves the imaging contrast and the nanoscale imaging capability of the NIR optical microscope, with the average contrast ratio increasing from 8.0% to 16.8%, thereby broadening its applications across a range of scientific and technological fields.