We propose a dynamic full-field optical coherence microscope imaging method using a
scientific complementary metal oxide semiconductor camera in conjunction with a demodulation
scheme based on Riesz transform and monogenic signals.
We illustrate the abilities of an advanced full-field optical coherence microscope (FF-OCM) setup for characterization of technical materials with internal micro-structures and present this technique also for dynamic process monitoring, as strain-stress tests. Additionally we briefly illustrate the potential of image processing in context of the chosen applications. Furthermore, contrast modification techniques based on Fourier plane filtering are discussed.
The principle of Fourier plane filtering in coherence probe microscopy (CPM) is demonstrated. It is shown that an edge
contrast enhancement can be obtained in an isotropic and anisotropic way for different technical materials containing
interfaces or internal micro-structures. Additionally image processing completes the CPM imaging and analysis.
We present a novel full-field low-coherence interference (LCI) microscope, which exhibits ultra-high axial resolution due
to a broadband super continuum light source and which is at the same time capable to generate different contrast modes
by using Fourier-plane filtering with a spatial light modulator. By changing the phase and spatial frequencies of the backreflected
wavefront of the specimen in the sample arm of the interferometer, we are able to change the contrast in the
depth-resolved LCI images. By displaying different filters on the SLM, as e.g. spiral phase, the resulting images provide
particular enhancement of edges and internal structures, and expose details within the specimen that are not visible in
normal bright-field mode.
In this paper it is demonstrated, how research in optical coherence tomography (OCT) for biomedical diagnostics
successfully triggered new developments in the field of mechanical material testing. With the help of a specifically
designed, compact and robust spectral domain polarization sensitive OCT (SD-PS-OCT) setup, which is operating at
1.55 μm, dynamic investigations of technical materials - like bulk polymers and composite samples - can be performed
under various conditions. Already by evaluating the speckle pattern of the standard SD-OCT images with advanced
image processing methods, valuable information on the deformation and flow characteristics of samples subjected to
tensile tests can be obtained. By additionally taking the birefringence properties into account, complementary knowledge
on the evolvement of the internal stress situation is obtained in a spatially resolved way.
We present directional filtering and coherence-enhancing diffusion (CED) as well as two-dimensional quadrature
demodulation for analysis of single frame retardation images, acquired with polarisation-sensitive optical
coherence tomography (PS-OCT). We compare different denoising techniques applied to stress-induced PS-OCT
images and the influence of selected pre-processing methods on the demodulation results.
Polarization-sensitive (PS) optical coherence tomography (OCT) allows for depth-resolved measurement of light polarizing properties of different layers in the human retina. Since their inherent polarizing properties are different, the retinal structures can be identified using PS-OCT. We present an improved PS-OCT instrument for in vivo imaging of healthy and diseased human retinas. The system is based on spectral-domain (SD) PS-OCT operating at an A-line rate of 20 kHz. Different scan patterns and trigger signals are controlled by a field-programmable gate array (FPGA). By integration of an additional detection channel in the source arm of the OCT system, scanning laser ophthalmoscope (SLO) images can be recorded. Images of healthy and diseased human retinas are presented.
Optical coherence tomography (OCT) is a contactless and non-invasive technique nearly exclusively applied for bio-medical imaging of tissues. Besides the internal structure, additionally strains within the sample can be mapped when OCT is performed in a polarization sensitive (PS) way. In this work, we demonstrate the benefits of PS-OCT imaging for non-biological applications. We have developed the OCT technique beyond the state-of-the-art: based on transversal ultra-high resolution (UHR-)OCT, where an axial resolution below 2 μm within materials is obtained using a femtosecond laser as light source, we have modified the setup for polarization sensitive measurements (transversal UHR-PS-OCT). We perform structural analysis and strain mapping for different types of samples: for a highly strained elastomer specimen we demonstrate the necessity of UHR-imaging. Furthermore, we investigate epoxy waveguide structures, photoresist moulds for the fabrication of micro-electromechanical parts (MEMS), and the glass-fibre composite outer shell of helicopter rotor blades where cracks are present. For these examples, transversal scanning UHR-PS-OCT is shown to provide important information about the structural properties and the strain distribution within the samples.
Optical coherence tomography (OCT), so far mainly used in the biomedical field, has a high potential as non-destructive and contactless technique for material characterization and analysis. For these applications, OCT systems with ultra-high resolution in the micrometer range and capable of high imaging speeds are required. In this work, we combine ultra-high resolution imaging using a femtosecond Ti:sapphire laser as light source with the concepts of transversal OCT. Based on acquisition by heterodyne detection via acousto-optic modulators (AOMs), and by using an xy-galvano scanner unit we are able to obtain en-face scans with sizes as large as 3 x 3 mm2 within a few seconds. The ultra-high resolution of our OCT system of 2.95 μm axially and 4 μm laterally, both in air, is shown to be essential for imaging of different compounds and fibre materials. We demonstrate the benefits of en-face scanning OCT for various applications in material investigation where in-plane information is of interest which can hardly be obtained by cross-sectional OCT.
In this paper the optical method based on multisample modification variable angle spectroscopic ellipsometry (VASE) is used to characterize thin films of ZnSe prepared by molecular beam epitaxy onto GaAs single crystal substrates. It is found that this method can be employed for determining the spectral dependences of the optical constants and values of the thicknesses of the films mentioned. Moreover, it is shown that using this method the RMS values of the heights and the values of the correlation length characterizing roughness irregularities of the upper boundaries of the films can be determined as well. The application of the method is illustrated by means of characterizing six samples of the ZnSe-films exhibiting different values of the thicknesses.
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