S. B. Ippolito

High spatial resolution subsurface microscopy

We present a high-spatial-resolution subsurface microscopy technique that significantly increases the numerical aperture of a microscope without introducing an additional spherical aberration. Consequently, the diffraction-limited spatial resolution is improved beyond the limit of standard subsurface microscopy. By realizing a numerical aperture of 3.4, we experimentally demonstrate a lateral spatial resolution of better than 0.23 μm in subsurface inspection of Si integrated circuits at near infrared wavelengths.

Toward nanometer-scale resolution in fluorescence microscopy using spectral self-interference

We introduce a new fluorescence microscopy technique that maps the axial position of a fluorophore with subnanometer precision. The interference of the emission of fluorophores in proximity to a reflecting surface results in fringes in the fluorescence spectrum that provide a unique signature of the axial position of the fluorophore. The nanometer sensitivity is demonstrated by measuring the height of a fluorescein monolayer covering a 12-nm step etched in silicon dioxide. In addition, the separation between fluorophores attached to the top or the bottom layer in a lipid bilayer film is determined. We further discuss extension of this microscopy technique to provide resolution of multiple layers spaced as closely as 10 nm for sparse systems.

Theoretical analysis of numerical aperture increasing lens microscopy

We present a detailed theoretical analysis and experimental results on a subsurface microscopy technique that significantly improves the light-gathering, resolving, and magnifying power of a conventional optical microscope. The numerical aperture increasing lens (NAIL) is a plano-convex lens placed on the planar surface of an object to enhance the amount of light coupled from subsurface structures within the object. In particular, a NAIL allows for the collection of otherwise inaccessible light at angles beyond the critical angle of the planar surface of the object. Therefore, the limit on numerical aperture increases from unity for conventional subsurface microscopy to the refractive index of the object for NAIL microscopy. Spherical aberration associated with conventional subsurface microscopy is also eliminated by the NAIL. Consequently, both the amount of light collected and diffraction-limited spatial resolution are improved beyond the limits of conventional subsurface microscopy. A theoretical optical model for imaging structures below the planar surface of an object, both with and without a NAIL, is presented. Experimental results demonstrating the predicted improvements in resolution of subsurface imaging are also presented.We present a detailed theoretical analysis and experimental results on a subsurface microscopy technique that significantly improves the light-gathering, resolving, and magnifying power of a conventional optical microscope. The numerical aperture increasing lens (NAIL) is a plano-convex lens placed on the planar surface of an object to enhance the amount of light coupled from subsurface structures within the object. In particular, a NAIL allows for the collection of otherwise inaccessible light at angles beyond the critical angle of the planar surface of the object. Therefore, the limit on numerical aperture increases from unity for conventional subsurface microscopy to the refractive index of the object for NAIL microscopy. Spherical aberration associated with conventional subsurface microscopy is also eliminated by the NAIL. Consequently, both the amount of light collected and diffraction-limited spatial resolution are improved beyond the limits of conventional subsurface microscopy. A theoretical optic...

Widefield subsurface microscopy of integrated circuits

We apply the numerical aperture increasing lens technique to widefield subsurface imaging of silicon integrated circuits. We demonstrate lateral and longitudinal resolutions well beyond the limits of conventional backside imaging. With a simple infrared widefield microscope (lambda(0) = 1.2 microm), we demonstrate a lateral spatial resolution of 0.26 microm (0.22 lambda(0)) and a longitudinal resolution of 1.24 microm (1.03 lambda(0)) for backside imaging through the silicon substrate of an integrated circuit. We present a spatial resolution comparison between widefield and confocal microscopy, which are essential in integrated circuit analysis for emission and excitation microscopy, respectively.

Immersion lens microscopy of photonic nanostructures and quantum dots

We describe recent experimental and theoretical advances in immersion lens microscopy for, both surface and subsurface imaging as applied to photonic nanostructures. We examine in detail the ability of sharp metal tips to enhance local optical fields for nanometer resolution microscopy and spectroscopy. Finally, we describe a new approach to nano-optics, that of combining solid immersion microscopy with tip-enhanced focusing and show how such an approach may lead to 20-nm resolution with unity throughput.

Subsurface microscopy of integrated circuits with angular spectrum and polarization control.

We investigate the effect of an annular pupil-plane aperture in confocal imaging while using an NA increasing lens. We show that focal spot shape is highly sensitive to both polarization and angular spectrum of the incoming light. We demonstrate a lateral spatial resolution of 145 nm (lambda(0)/9) in the direction perpendicular to the polarization direction.

A case study for optics: The solid immersion microscope

Microscopes are natural objects of study in introductory and upper level courses that cover optics because they are used in most science and engineering disciplines. The solid immersion microscope has been developed to study a variety of physical systems with high resolution and we suggest its inclusion in upper level optics courses. We briefly describe the solid immersion microscope in the context of geometrical optics and a desktop demonstration. We use the angular spectrum representation to calculate the focal fields produced by a conventional microscope and a solid immersion microscope. We also suggest a simple model for lens aberration and perform numerically the focal field calculations with and without aberrations to enable users to compare the performance of conventional and solid immersion microscopes. These calculations can help users develop intuition about the sensitivity of microscope performance to real-world manufacturing tolerances and to the limitations and capabilities of microscopy.

High Resolution, High Collection Efficiency in Numerical Aperture Increasing Lens Microscopy of Individual Quantum Dots

We demonstrate the application of a subsurface solid immersion technique to the photoluminescence spectroscopy of individual quantum dots. Contrasted with the conventional solid immersion microscopy, we used a numerical aperture increasing lens and moved the interface between the sample and the solid immersion lens away from the focal plane, thus diminished the influence of interface artifacts on the images obtained in a two-dimensional scan. Meanwhile, our technique has achieved a high spatial resolution of λ∕3 that is capable of resolving the spectroscopic features of single QDs. We also demonstrate that the collection efficiency of our system is six times better than that of a conventional confocal microscope with a high NA objective.

Diffraction of evanescent waves and nanomechanical displacement detection

Sensitive displacement detection has emerged as a significant technological challenge in mechanical resonators with nanometer-scale dimensions. A novel nanomechanical displacement detection scheme based upon the scattering of focused evanescent fields is proposed. The sensitivity of the proposed approach is studied using diffraction theory of evanescent waves. Diffraction theory results are compared with numerical simulations.

High resolution subsurface microscopy technique

The numerical aperture increasing lens (NAIL) technique increases the NA and subsequent resolution while preserving stigmatic imaging, and is therefore a significant improvement over standard optical microscopy for subsurface imaging at the diffraction limit. We give experimental data which demonstrates the NAIL technique capability.