1. Scanning Light-Diffracted Microscopy Hira Farooq,1,2, Sueli Skinner-Ramos,1,2 Luis Grave de Peralta,1,2 1Department of Physics and Astronomy, 2Nano Tech Center, Texas Tech University, Lubbock, TX 79409, USA
Processing Experimental Images Using SLDM Algorithm
Fourier Plane (FP) and Real Plane (RP) Experimental Images
Abstract
We simulated and experimentally demonstrated a novel sub-wavelength resolution microscopy technique by illuminating the sample with the hollow-cone of light produced by a ring-shaped condenser and scanning the diffracted light using a slit.
Introduction
We present a practical method for improving the resolution limit of a microscope-condenser combination where the sample is illuminated by a hollow-cone of light. The resolution improvement from λ/(2NAo), where λ is the wavelength of the light used for illumination and NAo is the numerical aperture of the objective lens, to λ/(NAo+NAc), where NAc is the numerical aperture of the condenser, can be notable when NAc >> NAo, which could occur in two important cases with practical applications. Due to the absence of condensers with NAc >> 1, this work involves experiments with NAo << 1 and NAc ~ 1 where a high-resolution image with the large FOV characteristic of small NAo is obtained. However, plasmonic ultrathin condensers (PUC) emitting a hollow-cone of light with NAc >> 1 have been predicted [1-3]; therefore, a combination of a PUC-microscope arrangement and the practical method for resolution improvement discussed here may result in a novel kind of optical nanoscope [2-3].
Using FPIM for Obtaining Initial Approximation for SLDM Algorithm
Fourier Plane Region Sampled by the Slit
Simulation Results
Imaging Technique
References
[1] D. B. Desai, D. Dominguez, A. A. Bernussi, and L. Grave de Peralta, “Ultra-thin condensers for optical subwavelength resolution microscopy,” J. Appl. Phys. 115, (2014).
[2] L. Grave de Peralta, “Metal slab superlens-negative refractive index versus inclined illumination: discussion,” JOSA A 32, (2015).
[3] S. Skinner-Ramos, H. Farooq, H. Alghasham, and L. Grave de Peralta, “Toward phase-recovery optical nanoscopes,” Journal of Physical Science and Application 7, (2017).
[4] M. Alotaibi, S. Skinner-Ramos, A. Alamri, B. Alharbi, M. Alfarraj, and L. Grave de Peralta, “Illumination direction multiplexing Fourier ptychographic microscopy using hemispherical digital condensers,” Applied Optics 56, (2017).
Conclusions
We presented an inexpensive but practical implementation of the Scanning Light-Diffracted Microscopy (SLDM) technique involving a ring-shaped condenser emitting a hollow-cone of light and a slit placed in the back focal plane of the objective lens. By varying the orientation of the slit, the diffracted light coming from the sample is scanned. A pair of FP and RP images was captured at each position of the slit. The experimental images were processed using a combination of the Fourier Plane Imaging Microscopy (FPIM) technique and a variation of the Illumination-Direction Multiplexing (IDM) Fourier Ptychographic Microscopy (FPM) algorithm, which rapidly converged to a high-resolution RP image surpassing the Rayleigh resolution limit. We foresee the development of novel plasmonic nanoscopes based on both, the experimental technique demonstrate in this work, but using a PUC with very large value of NAc, and in the processing of the experimental images using the SLDM algorithm presented here. In addition, we expect that the innovations demonstrated in this work will result in a simple, inexpensive and practical method for increasing the resolution limit of condenser-microscope arrangements which currently deploy in numerous characterization and biomedical laboratories.