High-resolution infrared Fourier ptychographic microscopy using InGaAs camera

Abstract

Imaging using infrared (IR) light sources has relatively long wavelengths compared to visible light, making it difficult to form small spot sizes. Furthermore, InGaAs cameras, widely used for infrared imaging with wavelengths exceeding 1000 nm, have larger pixels than silicon-based cameras used for visible light, making them unsuitable for high-resolution imaging. We propose a high-resolution IR Fourier ptychographic microscopy (FPM) technology consisting of an IR LED illuminator and a low-resolution InGaAs camera for high-resolution IR imaging. Using an objective lens with a numerical aperture (NA) of 0.4, we achieve a synthetic NA of 1.05 in the IR-FPM, which we experimentally verified through captured images from the USAF resolution chart. Furthermore, we demonstrate high-resolution imaging of internal cracks in Si wafers, leveraging the advantage of IR imaging that can penetrate Si substrates. The proposed method is expected to be widely utilized as a measurement technology in various industrial fields that use Si wafers substrates.