Proc. SPIE. 11056, Optical Measurement Systems for Industrial Inspection XI
KEYWORDS: Diffraction, Super resolution, Optical spheres, Polymers, Glasses, Interferometry, 3D modeling, Monte Carlo methods, Objectives, Semiconducting wafers
Scanning White Light Interferometry is a non-contacting method for three-dimensional (3D) surface characterization that provides Angstrom level vertical resolution and diffraction limited lateral resolution. This lateral resolution can be improved by implementing a photonic nanojet (PNJ) generating structure. The new method - Photonic Nanojet Interferometry (PNI) allows nanometer vertical resolution and lateral resolution better than 100 nm. In this work, a new design of a PNI system is proposed. The PNJ generating structure is a high refractive index microsphere embedded in a polymer material. We model the entire PNI objective in commercial software (Rsoft FullWAVE) and choose optimal parameters for the construct in such a way, that the working distance (FoV) is maximized while the width of the PNJ is kept below the diffraction limit. To test the new system, we imaged the data layer of a recordable Blu-ray Disc (BD). The results show that the proposed interferometer has two times higher magnification and two times larger field of view compared to the previous design featuring a 11 μm melamine formaldehyde micro-sphere. The new design also increases the fringe contrast by 1.5 times and provides easier handling of big samples by allowing them to be scanned.
Proc. SPIE. 11056, Optical Measurement Systems for Industrial Inspection XI
KEYWORDS: Microscopes, Diffraction, Finite-difference time-domain method, Super resolution, Optical spheres, Light scattering, Monte Carlo methods, Near field, Objectives, Device simulation
We simulate the image generated by a microsphere residing in contact on top of an exposed Blu-ray disk surface, when observed by a conventional microscope objective. While microsphere lenses have been used to focus light beyond the diffraction limit and to produce super-resolution images, the nature of the light-sample interaction is still under debate. Simulations in related articles predict the characteristics of the photonic nanojet (PNJ) formed by the microsphere, but so far, no data has been published on the image formation in the far-field. For our simulations, we use the open source package Angora and the commercial software RSoft FullWave. Both packages implement the Finite Difference Time Domain (FDTD) approach. Angora permits us to accurately simulate microscope imaging at the diffraction limit. The RSoft FullWave is able to record the steady-state complex electrical and magnetic fields for multiple wavelengths inside the simulation domain. A microsphere is simulated residing on top of a dielectric substrate featuring sub-wavelength surface features. The scattered light is recorded at the edges of the simulation domain and is then used in the near-field to far-field transformation. The light in the far field is then refocused using an idealized objective model, to give us the simulated microscope image. Comparisons between the simulated image and experimentally acquired microscope images verify the accuracy of our model, whereas the simulation data predicts the interaction between the PNJ and the imaged sample. This allows us to isolate and quantify the near-field patterns of light that enable super-resolution imaging, which is important when developing new micro-optical focusing structures.
Proc. SPIE. 10539, Photonic Instrumentation Engineering V
KEYWORDS: Diffraction, Super resolution, Stereoscopy, Polymers, Image resolution, Near field scanning optical microscopy, 3D metrology, 3D vision, 3D image processing, Near field optics
Recently, 3D label-free super-resolution profilers based on microsphere-assisted scanning white light interferometry were introduced having vertical resolution of few angstroms (Å) and a lateral resolution approaching 100 nm. However, the use of a single microsphere to generate the photonic nanojet (PNJ) limits their field of view. We overcome this limitation by using polymer microfibers to generate the PNJ. This increases the field of view by order of magnitude in comparison to the previously developed solutions while still resolving sub 100 nm features laterally and keeping the vertical resolution in 1nm range. To validate the capabilities of our system we used a recordable Blu-ray disc as a sample. It features a grooved surface topology with heights in the range of 20 nm and with distinguishable sub 100 nm lateral features that are unresolvable by diffraction limited optics. We achieved agreement between all three measurement devices across lateral and vertical dimensions. The field of view of our instrument was 110 μm by 2 μm and the imaging time was a couple of seconds.
We present the design of a novel scatterometer for precise measurement of the angular Mueller matrix profile of a mm- to µm-sized sample held in place by sound. The scatterometer comprises a tunable multimode Argon-krypton laser (with possibility to set 1 of the 12 wavelengths in visible range), linear polarizers, a reference photomultiplier tube (PMT) for monitoring the beam intensity, and a micro-PMT module mounted radially towards the sample at an adjustable radius. The measurement angle is controlled by a motor-driven rotation stage with an accuracy of 15’. The system is fully automated using LabVIEW, including the FPGA-based data acquisition and the instrument’s user interface. The calibration protocol ensures accurate measurements by using a control sphere sample (diameter 3 mm, refractive index of 1.5) fixed first on a static holder followed by accurate multi-wavelength measurements of the same sample levitated ultrasonically.
To demonstrate performance of the scatterometer, we conducted detailed measurements of light scattered by a particle derived from the Chelyabinsk meteorite, as well as planetary analogue materials. The measurements are the first of this kind, since they are obtained using controlled spectral angular scattering including linear polarization effects, for arbitrary shaped objects. Thus, our novel approach permits a non-destructive, disturbance-free measurement with control of the orientation and location of the scattering object.
We describe a setup for precise multi-angular measurements of light scattered by mm- to μm-sized samples. We present
a calibration procedure that ensures accurate measurements. Calibration is done using a spherical sample (d = 5 mm, n =
1.517) fixed on a static holder. The ultimate goal of the project is to allow accurate multi-wavelength measurements (the
full Mueller matrix) of single-particle samples which are levitated ultrasonically.
The system comprises a tunable multimode Argon-krypton laser, with 12 wavelengths ranging from 465 to 676 nm, a
linear polarizer, a reference photomultiplier tube (PMT) monitoring beam intensity, and several PMT:s mounted radially
towards the sample at an adjustable radius. The current 150 mm radius allows measuring all azimuthal angles except for
±4° around the backward scattering direction. The measurement angle is controlled by a motor-driven rotational stage
with an accuracy of 15’.
Super-resolution photonic nanojet interferometry is a new modality for 3D label-free super-resolution imaging. We
present a comparative study of the photonic nanojet interaction with a polymer sample. We use numerical modelling to
understand the interaction between a microsphere-induced photonic nanojet and the polymer sample. The numerical
model employs the same set of input parameters (melamine formaldehyde microsphere with a diameter of 11 μm and a
refractive index of 1.68), as in our experiments. The interaction is described using the Finite-Difference Time-Domain
method applied on a finely discretized mesh. The knowledge gained using the verified and validated model, will be used
to conduct numerical simulations in a wider parameter space. This enables optimizing the design of 3D-interferometric
super-resolution microscopes.
We describe a setup for measuring the full angular Mueller matrix profile of a single mm- to μm-sized sample, and verify the experimental results against a theoretical model. The scatterometer has a fixed or levitating sample, illuminated with a laser beam whose full polarization state is controlled. The scattered light is detected with a combination of wave retarder, linear polarizer, and photomultiplier tube that is attached to a rotational stage. The first results are reported.
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