We investigate graphene and graphene layers on different substrates by monochromatic and white-light confocal Rayleigh scattering microscopy. The image contrast depends sensitively on the dielectric properties of the sample as well as the substrate geometry and can be described quantitatively using the complex refractive index of bulk graphite. For a few layers (<6), the monochromatic contrast increases linearly with thickness. The data can be adequately understood by considering the samples behaving as a superposition of single sheets that act as independent two-dimensional electron gases. Thus, Rayleigh imaging is a general, simple, and quick tool to identify graphene layers, which is readily combined with Raman scattering, that provides structural identification.

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Rayleigh Imaging of Graphene and Graphene Layers

Optical coherence tomography (OCT), a method for depth-resolved imaging within turbid media based on the concept of low-coherence interferometry, rapidly evolved in the recent years with the development of a multitude of new functionalities and modalities. Biomedical research and diagnostics have been up to now the main driving forces for the reported applications and progress in OCT. The characteristics of OCT, precisely the ability to provide high-resolution images in a contact-free way, render this technique also attractive for a broad spectrum of research topics and applications outside the biomedical field. Consequently, a variety of novel applications for OCT and developments for the method itself have started to emerge. In this review we will give a detailed overview of the so far presented OCT-based methods and applications, ranging from dimensional metrology, material research and non-destructive testing, over art diagnostics, botany, microfluidics to data storage and security applications, and include new data from a study on penetration depths in various polymer materials as well as on birefringence imaging of different crystalline polymer structures. Finally, advanced and related OCT techniques are presented with high potential for future applications outside the biomedical field.

Beyond biomedicine: a review of alternative applications and developments for optical coherence tomography

Interference microscopy plays a central role in noncontact strategies for process development and quality control, providing full 3D measurement of surface characteristics that influence the functional behavior of manufactured parts. Here I briefly review the history and principles of this important technique, then concentrate on the details of hardware, software, and applications of interference microscopy using phase-shifting and coherence scanning measurement principles. Recent advances considered here include performance improvements, vibration robustness, full color imaging, accommodation of highly sloped surfaces, correlation to contact methods, transparent film analysis, and international standardization of calibration and specification.

Principles of interference microscopy for the measurement of surface topography

Combining phase and coherence information for improved precision in white-light interference microscopy requires a robust strategy for dealing with the inconsistencies between these two types of information. We correct for these inconsistencies on every measurement by direct analysis of the difference map between the coherence and the phase profiles. The algorithm adapts to surface texture and noise level and dynamically compensates for optical aberrations, distortions, diffraction, and dispersion that would otherwise lead to incorrect fringe order. The same analysis also provides the absolute height data that are essential to relational measurements between disconnected surfaces.

Determination of fringe order in white-light interference microscopy

A method including comparing information derivable from a scanning interferometry signal for a first surface location of a test object to information corresponding to multiple models of the test object, wherein the multiple models are parametrized by a series of characteristics for the test object. The derivable information being compared may relate to a shape of the scanning interferometry signal for the first surface location of the test object.

Profiling complex surface structures using scanning interferometry

White-light scanning interferometry is increasingly used for precision profile metrology of engineering surfaces, but its current applications are limited primarily to opaque surfaces with relatively simple optical reflection behavior. A new attempt is made to extend the interferometric method to the thickness-profile measurement of transparent thin-film layers. An extensive frequency-domain analysis of multiple reflection is performed to allow both the top and the bottom interfaces of a thin-film layer to be measured independently at the same time by the nonlinear least-squares technique. This rigorous approach provides not only point-by-point thickness probing but also complete volumetric film profiles digitized in three dimensions.

Thickness-profile measurement of transparent thin-film layers by white-light scanning interferometry

A method and apparatus for measuring the three-dimensional surface shape of an object using color informations of light reflected by the object. The method and apparatus for measuring the three-dimensional surface shape of the object, in which a real-time measurement of the three-dimensional surface is performed by projecting a beam of light having color information onto the object and detecting color distribution information according to levels of the object, thereby obtaining level information of the object.

Method and apparatus for measuring the three-dimensional surface shape of an object using color informations of light reflected by the object

White light scanning interferometry generates short coherence interferograms whose fringe visibility is narrowly localized along the scanning dimension so that the optical path difference between the test and reference beams can be scaled without 2(pi) -ambiguity. Much attention has been paid during last two decades to the 3D surface mapping using white light scanning interferometry, and as results, quite a few noble different techniques are available in the published literature. The techniques differ from each other in the intricate way of fringe data processing, but just about all of them are effective in measuring top profiles of opaque surfaces with nanometer precision. However, when the surface is coated with transparent thin films layers, multiple reflections occur from the boundaries of film layers to produce complicate overlapped interferograms which are not readily treated by the existing techniques. The thickness measurement technique presented in this paper is as an extended version of the frequency domain analysis of white light interferometry. Special attempt is made to provide a means of interpreting interferograms of multiple reflection so that physical properties of thin film layers are precisely identified utilizing sampled phase distribution in the spectral frequency domain. In conclusion, the technique is capable of not only probing thickness point by point but also providing complete volumetric film digitized in three dimensions.

White light scanning interferometry for thickness measurement of thin film layers

We present an automatic inspection system which been developed to evaluate the geometric tolerances of the optical fiber connectors with an dimensional accuracy of. The main part of the inspection system comprises a series of machine vision and laser scanning probes to measure the internal and external circle diameters along with concentricity by making the most of advanced edge detection algorithms. Actual experimental results obtained through various repeatability tests demonstrate that the system well satisfies the required industrial demands for in-situ inspection of optical fiber connections in real manufacturing environment.

Automatic Inspection of Geometric Accuracy of Optical Fiber Single Ferrules

We present an automatic inspection system developed to evaluate the geometric tolerance of the optical fiber connectors to a dimensional accuracy of 0.1 micron. The main part of the inspection system comprises a series of machine vision devices and laser scanning probes to measure the internal and external circle diameters along with their concentricity by making the most of advanced digital edge detection algorithms. Actual experimental results obtained through various repeatability tests demonstrate that the developed system well satisfies the required industrial demands for in-situ inspection of optical fiber connectors in real manufacturing environment.

Gee-Hong Kim

Papers

Thickness-profile measurement of transparent thin-film layers by white-light scanning interferometry

Method and apparatus for measuring the three-dimensional surface shape of an object using color informations of light reflected by the object

White light scanning interferometry for thickness measurement of thin film layers

Automatic Inspection of Geometric Accuracy of Optical Fiber Single Ferrules

Automatic inspection of geometric accuracy of optical fiber ferrules by machine vision