Photonic nanojets generated using square-profile microsteps.

Area of Science:

• Optics and Photonics
• Nanotechnology
• Materials Science

Background:

• Sub-wavelength optical phenomena are crucial for advancing nanoscale imaging and manipulation.
• Creating localized, high-intensity light fields below the diffraction limit remains a significant challenge.

Purpose of the Study:

• To experimentally demonstrate the generation of photonic nanojects using microstructured silica substrates.
• To investigate the relationship between microstep dimensions and the characteristics of the generated light field.

Main Methods:

• Fabrication of square-profile microsteps on a silica substrate with varying side lengths (0.4-0.8 μm) and a fixed height (500 nm).
• Illumination of the microsteps using a linearly polarized laser beam (λ=633 nm) transmitted through the substrate.
• Experimental characterization of the near-surface enhanced-intensity regions (photonic nanojects) using optical microscopy.

Main Results:

• Observed photonic nanojects with intensities up to six times higher than the incident laser light.
• Measured full width at half-maximum (FWHM) diameters of the nanojects ranging from 0.39λ to 0.47λ, significantly below the diffraction limit of 0.51λ.
• Demonstrated that the focal position (inside or outside the step) depends on the microstep side length relative to the wavelength of light.

Conclusions:

• Square-profile microsteps can effectively generate sub-diffraction limit photonic nanojects with enhanced intensity.
• The dimensions of the microsteps play a critical role in controlling the localization and characteristics of these optical features.
• These findings offer a pathway for developing novel optical elements for nanoscale applications.