In this paper, we present a Wavefront Division (WD) Fourier domain Swept Source Optical Coherence Tomography (SS-OCT) configuration. The presented WD-SS-OCT configuration has two key features that are discussed in this contribution. First, there is the possibility of variable splitting and flexible adjustment of the splitting ratio between the sample and the reference. This enables an adaptation to differing reflective and scattering features of various samples. The second feature is related to the increased throughput of the interferometer design. The use of polarization optics makes it possible to almost eliminate back-reflection losses completely to the source (up to 50% of the intensity in standard amplitude division-based OCT). WD-OCT configuration has its challenges compared to conventional OCT systems based on amplitude splitting. Nevertheless, the proposed design has also specific options and flexibilities that are worth to be shared with the OCT community.
We provide an overview of optical coherence tomography (OCT) applied in the field of non-destructive testing (NDT). The applications include examples for structural polymer material testing at mesoscopic size scale, visualizing and validating internal sub-surface micro-defects, or characterizing the coating and bonding quality in multilayer samples. Furthermore, dynamical processes observed by OCT in their temporal progress can be demonstrated in the context of NDT as well as multimodal settings for gaining structural and specific insights on the materials tested. We will also regard the challenges for performing dimensional measurements and optical metrology by OCT imaging. In addition, novel developments and trends at illumination and detection sites will be discussed as essential components and requirements for the progress in OCT technology. This includes newly accessible spectral ranges under the view point of sensing as well as adaptable learning tools under the view point of data and image processing, which will round off the topic.
Novel types of supercontinuum sources radiating in the infrared (IR) spectral region provide ultra-broadband spectral coverage and maintain distinctive laser-like properties of emission such as brightness, spatial coherence and high power. Being a perfectly suitable light source for mid-infrared optical coherence tomography (OCT) and spectroscopy, supercontinuum sources initiated a significant amount of recent developments in these fields and promise to be a gamechanging factor in the nearest future. In this paper, we exhibit a simple, optimized and relatively cost-effective system operating in near and mid-infrared ranges and combining OCT and co-registered IR spectroscopy. The performance of the OCT modality of the setup is evaluated with respect to the sensitivity and roll-off. Due to reduced scattering inherited with the new spectral window, we achieve the enhancement in the penetration depth in artificial paintings, ceramics and pottery. Furthermore, the hyperspectral data is used to supplement structural information and access to the chemical composition of the sample. The gained results reveal the potential of the multimodal system for non-destructive testing, art and cultural objects diagnosis.
This paper illustrates specific features and use of optical coherence tomography (OCT) in the raster-scanning and in comparison in the full field version of this imaging technique. Cases for nondestructive testing are discussed alongside other application schemes. In particular monitoring time-dependent processes and probing of birefringent specimens are considered here. In the context of polymer testing birefringence mapping may often provide information about internal strain and stress states. Recent results obtained with conventional raster-scanning OCT systems, with (dual and single-shot) full field OCT configurations, and with polarization-sensitive versions of (full field) OCT are presented here.
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.
Time-of-flight (TOF) full-field range cameras use a correlative imaging technique to generate three-dimensional measurements of the environment. Though reliable and cheap they have the disadvantage of high measurement noise and errors that limit the practical use of these cameras in industrial applications. We show how some of these limitations can be overcome with standard image processing techniques specially adapted to TOF camera data. Additional information in the multimodal images recorded in this setting, and not available in standard image processing settings, can be used to improve reduction of measurement noise. Three extensions of standard techniques, wavelet thresholding, adaptive smoothing on a clustering based image segmentation, and an extended anisotropic diffusion filtering, make use of this information and are compared on synthetic data and on data acquired from two different off-the-shelf TOF cameras. Of these methods, the adapted anisotropic diffusion technique gives best results, and is implementable to perform in real time using current graphics processing unit (GPU) hardware. Like traditional anisotropic diffusion, it requires some parameter adaptation to the scene characteristics, but allows for low visualization delay and improved visualization of moving objects by avoiding long averaging periods when compared to traditional TOF image denoising.
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.
In order to measure the 3D structure of a number of objects a comparably new technique in computer vision
exists, namely time of flight (TOF) cameras. The overall principle is rather easy and has been applied using
sound or light for a long time in all kind of sonar and lidar systems. However in this approach one uses modulated
light waves and receives the signals by a parallel pixel array structure. Out of the travelling time at each pixel one
can estimate the depth structure of a distant object. The technique requires measuring the intensity differences
and ratios of several pictures with extremely high accuracy; therefore one faces in practice rather high noise
levels. Object features as reflectance and roughness influence the measurement results. This leads to partly
high noise levels with variances dependent on the illumination and material parameters. It can be shown that
a reciprocal relation between the variance of the phase and the squared amplitude of the signals exists. On the
other hand, objects can be distinguished using these dependencies on surface characteristics. It is shown that
based on local variances assigned to separated objects appropriate denoising can be performed based on Wavelets
and edge-preserving smoothing methods.
KEYWORDS: Proteins, Detection and tracking algorithms, Denoising, Wavelets, Microscopy, Anisotropic diffusion, Convolution, Digital filtering, Signal to noise ratio, Wavelet transforms
The in vivo imaging of proteins represents a promising technique for understanding the processes taking place at cellular level. Tracking the single proteins manually is tedious and the results are difficult to replicate. Due to the imaging characteristics the automation of the task is difficult. In this paper we study the problem of denoising of the image sequences, spot detection and data association. The 3D version of three denoising algorithms were implemented: adaptive mean filtering, anisotropic diffusion and spatial-tonal convolution. Their effect combined with the spot detection based on the à trous wavelet transform is studied. Finally, a point tracking algorithm is applied having as input the spots detected in the previous step. The algorithm can handle new track creation, track termination as well as one frame occlusions. The paper concludes with a discussion of the results and further work.
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