We present an alternative optical method to estimate the temperature during the cooling process of a liquid using digital holographic interferometry (DHI). We make use of phase variations that are linked to variations in the refractive index and the temperature property of a liquid. In DHI, a hologram is first recorded using an object beam scattered from a rectangular container with a liquid at a certain reference temperature. A second hologram is then recorded when the temperature is decreased slightly. A phase difference between the two holograms indicates a temperature variation, and it is possible to obtain the temperature value at each small point of the sensed optical field. The relative phase map between the two object states is obtained simply and quickly through Fourier-transform method. Our experimental results reveal that the temperature values measured using this method and those obtained with a thermometer are consistent. We additionally show that it is possible to analyze the heat-loss process of a liquid sample in dynamic events using DHI.
Phase unwrapping is an intermediate step for interferogram analysis. A smooth phase associated with an
interferogram can be estimated using a curve mesh of functions. Each of these functions can be approximated
by a linear combination of basis functions. In some cases constraints are needed to solve the phase unwrapping
problem, for example, when estimated values never can be negative. In this work it is proposed a method for
phase unwrapping using a set of functions in a mesh which are lineal combinations of Chebyshev polynomials.
Results show good performance when applied to noisy and noiseless synthetic images.
The large number of projections needed for tomographic reconstruction makes prohibitive the use of algebraic methods for fast phase object reconstruction. However, for smooth and continuous phase objects, the reconstruction can be performed with few projections by using an algorithm that approximates the phase as a linear combination of gaussian basis functions. This work presents an accurate algebraic reconstruction of a flame temperature from two independent interferometers using a He-Ne laser (623.8nm).
Refractive index, temperature, pressure, velocity and many other physical magnitudes of phase objects in the refraction less limit are of great interest in engineering and science. Optical tomography is a technique used to estimate these magnitudes. For axially symmetrical phase objects the tomographic reconstruction can be carried out from just one projection when using Abel transform. However, for noisy projections the reconstruction shows low quality. This quality can be improved when using the Kalman filter to compute the inverse Abel Transform. In this paper a tomographic reconstruction method for syntectic axially symmetrical phase objects using Kalman filter is presented.
Phase unwrapping is an intermediate step for interferogram analysis. The phase associated with an interferogram can be estimated using a curve mesh of functions. Each of these functions can be approximated by a linear combination of basis functions. Chebyshev polynomials in addition to being a family of orthogonal polynomials can be defined recursively. In this work a method for phase unwrapping using Chebyshev polynomials is proposed. Results show good performance when applied to synthetic images without noise and also to synthetic images with noise.
Phase wrapping is an intermediate step ffor interferometry analysis. When phase is smooth, its unwrapping can be carried out fitting local planes with finite extension at each point of the phase gradient. We propose a method easy to implement that spends the same computation time than those techniques based on basis functions.
KEYWORDS: Holograms, Digital holography, 3D metrology, Sensors, Holography, Beam splitters, Optical resolution, 3D image processing, Digital recording, Image processing
In this work we present an extension of the use of three different lasers and only one high resolution monochrome sensor.
Besides the advantage to obtain the 3D deformation in just two images it is now possible due the geometry of the optical
setup to obtain the strain gradients in the object. The system records two consecutive images where each one contains
three holograms in it. This configuration gives the opportunity to use long coherence length lasers which allows the
measurement of large object areas. A series of digital holographic interferograms are recorded for a particular metallic
sample during a well known mechanical deformation. From the system it is possible to obtain in just a couple of images
the orthogonal displacement components u, v and w and then the strain gradient maps. Latter gives more information
about the mechanical response for an object during a micro deformation.
A simultaneous 2-D pulsed digital holographic setup that incorporates a rigid endoscope is used to inspect hidden object areas in order to measure microstrains. The system was tested on the internal surface of a harmonically vibrating rectangular metal box with a fracture on its surface. The simultaneous setup allows the acquisition of displacement data from two different object illumination positions at the same time, so that the system is capable of studying nonrepeatable dynamic events. Further analysis using displacement data generates a gradient strain map where the fracture is successfully detected with the corresponding strain magnitude and direction quantified.
Separation of the surface strain gradient as a function of x and y was achieved using three-dimensional (3-D) digital holographic interferometry. The optical setup is capable of independently determining the x, y, and z displacements of the object surface. The magnitude contributions of the dependent, or interconnected, strain gradients are calculated from the normal strain gradients. In order to simplify the mathematical model, objects with smooth surfaces were considered and also only small static loads were applied to deform them. The 3-D information thus gathered is analyzed in order to obtain the x and y strain gradients. Each gradient is then processed to obtain a pair of mutually dependent gradient maps. These maps are shown for the x and y axes in a 3-D sparse vector map that changes according to the strain present on the object.
ESPI and 3D pulsed Digital Holography have been applied to detect inhomogeneities inside a metal cylinder. A shaker was employed to produce a mechanical wave that propagates through the inner structure of the cylinder in such a way that it generates vibrational resonant modes on the cylinder surface. An out of plane ESPI optical sensitive configuration was used to detect vibrational resonant modes. A 3D multi-pulse digital holography system was used to obtain quantitative deformation data of the dynamically moving cylinder. The local decrease in structural stiffness inside the cylinder due to an inhomogeneity produces an asymmetry in the resonant mode shape. Results show that the inhomogeneity produces an asymmetry in its vibrational resonant modes. The method may be reliably used to study and compare data from inside homogeneous and inhomogeneous solid materials.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.