We use a digital holographic interferometric setup to assess, as a proof of concept, two state-of-the-art sensors (CMOS and sCMOS cameras) that are widely used in nondestructive testing (NDT). This interferometric study is intended to evaluate the image quality recorded by any camera used in NDT. The assessing relies on the quantification of the optical phase information recovered by the cameras used for this study. For this, we calculate the signal-to-noise ratio, correlation coefficient, and quality index (Q-index) as main figures-of-merit. As far as we know, the Q-index has not been used for evaluation of the optical phase coming from image holograms. The CMOS and sCMOS sensors used record the same deformation event under the same experimental conditions. The experiment involves the inspection of a large sample (>1 m2 of area) which implies low illumination conditions for the imaging sensors. The retrieved CMOS optical phase shows artifacts that are not observed in the sCMOS. An analysis of these two groups of interferometric images is presented and discussed. The methodology set forth here can be applied to evaluate other sensors such as CCDs and EM-CCDs.
A study in porcine femoral bones with and without the presence of cortical drilling is presented. An out of plane digital holographic interferometer is used to retrieve the optical phase during the controlled compression tests. These tests try to simulate physiological deformations in postmortem healthy bones and compare their mechanical response with those having a cortical hole. The cortical drilling technique is widely used in medical procedures to fix plaques and metallic frames to a bone recovering from a fracture. Several materials and drilling techniques are used for this purpose. In this work we analyze the superficial variations of the bone when different drilling diameters are used. By means of the optical phase it is possible to recover the superficial deformation of the tissue during a controlled deformation with high resolution. This information could give a better understand about the micro structural variations of the bone instead of a bulk response. As proof of principle, several tests were performed to register the modes and ranges of the displacements for compressive loads. From these tests notorious differences are observed between both groups of bones, having less structural stiffness the drilled ones as expected. However, the bone's characteristic to absorb and adjust itself due the load is also highly affected according to the number of holes. Results from different kind of samples (undrilled and drilled) are presented and discussed in this work.
Industrial applications of embedded materials have been increased in the recent years as the study of their mechanical properties. A particular interest is their homogeneousness which will determine a significant improvement or decay in the possible application. The optical system proposed here can show the internal micro structure and the internal displacements along a scanned volume through consecutives 2D tomographic and optical phase images. The volumetric information is retrieved by means of a liner stage which avoids the use of expensive tilting devices. Results show the response of homogeneous and in-homogeneous PMMA samples during controlled tests in order to find the simplest one which determines the sample’s condition.
We present an analysis of the imaging performance of two state-of-the-art sensors widely used in the nondestructive- testing area (NDT). The analysis is based on the quantification of the signal-to-noise (SNR) ratio from an optical phase image. The calculation of the SNR is based on the relation of the median (average) and standard deviation measurements over specific areas of interest in the phase images of both sensors. This retrieved phase is coming from the vibrational behavior of a large object by means of an out-of-plane holographic interferometer. The SNR is used as a figure-of-merit to evaluate and compare the performance of the CMOS and scientific CMOS (sCMOS) camera as part of the experimental set-up. One of the cameras has a high speed CMOS sensor while the other has a high resolution sCMOS sensor. The object under study is a metallically framed table with a Formica cover with an observable area of 1.1 m2. The vibration induced to the sample is performed by a linear step motor with an attached tip in the motion stage. Each camera is used once at the time to record the deformation keeping the same experimental conditions for each case. These measurements may complement the conventional procedures or technical information commonly used to evaluate a camera´s performance such as: quantum efficiency, spatial resolution and others. Results present post processed images from both cameras, but showing a smoother and easy to unwrap optical phase coming from those recorded with the sCMOS camera.
Current industrial demand for optical nondestructive testing includes the displacement analysis of large object areas. This paper reports on the use of a digital holographic interferometer to measure displacements over an area of 1.14 m2. The object under study is a framed working table covered with a Formica layer fixed to a granite bench, and it is observed and illuminated employing a high speed and high resolution camera and a continuous wave high output power laser, respectively. A stabilization procedure needs to be established as long illumination distances are required in order to retrieve the entire surface optical phase during a series of continuous deformations. As a proof of principle, two different tests are presented: the first involves a slow continuous loading process and the second a vibration condition. The wrapped phase and displacement maps are both displayed.
Recently, we introduced a Digital Optoelectronic Holographic System (DOEHS) for measurement of acoustically
induced deformations of the human tympanic membrane (TM) in order to study and diagnose pathologic conditions of
the middle-ear. The DOEHS consists of laser-delivery illumination (IS), optical head (OH), image-processing computer
(IP), and positioning arm (PS) subsystems. Holographic information is recorded by a CCD and numerically
reconstructed by Fresnel approximation. Our holographic otoscope system is currently deployed in a clinic and is
packaged in a custom design. Since digital holography is a high sensitivity measurement technique and the interfering
light waves travel along different paths, it makes measurements acquired by DOEHS susceptible to external vibrations.
In order to avoid this susceptibility, we are testing a shearography setup as OH. Shearography presents same advantages
as holographic interferometry, but it is less susceptible to vibration and external noise, which is a characteristic needed
for the use of our techniques in a clinical environment. In this paper we present work in progress in our development of a
shearography technique based on a Mach-Zehnder configuration as OH and demonstrate its application by quantifying
vibrations modes in thin membranes, including human TM. Results are compared with those obtained with DOEHS.
In this paper, we present advances on our development of an optoelectronic holographic computing platform with the
ability to quantitatively measure full-field-of-view nanometer-scale movements of the tympanic membrane (TM). These
measurements can facilitate otologists' ability to study and diagnose hearing disorders in humans. The holographic
platform consists of a laser delivery system and an otoscope.
The control software, called LaserView, is written in Visual C++ and handles communication and synchronization
between hardware components. It provides a user-friendly interface to allow viewing of holographic images with
several tools to automate holography-related tasks and facilitate hardware communication. The software uses a series of
concurrent threads to acquire images, control the hardware, and display quantitative holographic data at video rates and
in two modes of operation: optoelectronic holography and lensless digital holography.
The holographic platform has been used to perform experiments on several live and post-mortem specimens, and is to be
deployed in a medical research environment with future developments leading to its eventual clinical use.
Current ear examination procedures provide mostly qualitative information which results in insufficient or erroneous
description of the patient's hearing. Much more quantitative and accurate results can be achieved with a holographic
otoscope system currently under development. Various ways of accurate positioning and stabilization of the system in
real-life conditions are being investigated by this project in an attempt to bring this new technology to the hospitals and
clinics, in order to improve the quality of the treatments and operations of the human ear.
The project is focused at developing a mechatronic system capable of positioning the holographic otoscope to the
patient's ear and maintaining its relative orientation during the examination. The system will be able to be guided by the
examiner, but it will maintain the chosen position automatically. To achieve that, various trajectories are being measured
for existing otoscopes being guided by doctors in real medical conditions. Based on that, various kinematic
configurations are to be synthesized and their stability and accuracy will be simulated and optimized with FEA. For
simplification, the mechanism will contain no actuators, but only adjustable friction elements in a haptic feedback
control system. This renders the positioning system safe and easily applicable to current examination rooms. Other
means of stabilization of the system are being investigated such as custom designed packaging of all of the otoscope
subsystems, interferometrically compensating for the heartbeat induced vibration of the tympanic membrane as well as
methods for monitoring and active response to the motion of the patient's head.
A novel technique based on the use of a three Gaussian beam interferometer to obtain roughness information about
smooth optical surfaces is described. The technique is based on the heterodinization of three coherent optical beams. One
of the beams is used as a probe beam after being focused and reflected from the surface under test. A second beam is
generated to be reflected by a reference surface. The last beam is obtained from the first diffraction order of a Bragg cell
and thus, it is shifted in its temporal frequency. The three beams are coherently added at the sensitive plane of a
photodetector that integrates the overall intensity of the beams. It will be demonstrated analytically that the electrical
signal at the output of the photodetector is a time varying signal whose amplitude is proportional to the surface's local
vertical height. The frequency response of the proposed system is characterized experimentally by measuring the profile
of three different blazed-gratings. Once the system is calibrated, we present measurements of the roughness of an optical