Imaging photonic crystals using hemispherical digital condensers and phase-recovery techniques

Area of Science:

• Optical microscopy
• Nanophotonics
• Materials science

Background:

• Fourier ptychographic microscopy (FPM) and dual-space microscopy (DSM) are advanced phase-recovery imaging techniques.
• Imaging sub-wavelength structures like photonic crystals presents significant resolution challenges.
• Hemispherical digital condensers (HDC) offer unique illumination control but can introduce artifacts.

Purpose of the Study:

• To experimentally evaluate the capability of FPM and DSM for imaging photonic crystals below the Rayleigh resolution limit.
• To investigate discrepancies between simulated and experimental results for FPM and DSM.
• To identify and mitigate artifacts affecting FPM performance with an HDC.

Main Methods:

• Implementation of FPM and DSM using a hemispherical digital condenser (HDC).
• Phase-recovery algorithms applied to experimental image data.
• Comparative analysis of imaging performance for periodic structures below the diffraction limit.
• Systematic investigation of optical reflections within the HDC setup.

Main Results:

• Simulations predicted both FPM and DSM could resolve photonic crystals below the Rayleigh limit.
• Experimental results showed DSM successfully imaged sub-diffraction limit structures, while FPM initially failed.
• Unwanted reflections within the HDC were identified as the cause of FPM's experimental failure.
• Modifying illumination to a single-directional source eliminated reflections and restored FPM's capability.

Conclusions:

• FPM, when optimized by mitigating HDC reflections, can image photonic crystals below the Rayleigh resolution limit.
• DSM offers a viable alternative for sub-diffraction limit imaging, but FPM can achieve similar performance with proper setup.
• Careful consideration of optical artifacts, such as reflections, is crucial for successful high-resolution microscopy experiments.