Measurements of concentration differences between liquid mixtures using digital holographic interferometry

We present an alternative method to detect and measure the concentration changes in liquid solutions. The method uses Digital Holographic Interferometry (DHI) and is based on measuring refractive index variations. The first hologram is recorded when a wavefront from light comes across an ordinary cylindrical glass container filled with a liquid solution. The second hologram is recorded after slight changing the liquid’s concentration. Differences in phase obtained from the correlation of the first hologram with the second one provide information about the refractive index variation, which is directly related to the changes in physical properties related to the concentration. The method can be used − with high sensitivity, accuracy, and speed − either to detect adulterations or to measure a slight change of concentration in the order of 0.001 moles which is equivalent to a difference of 0.003 g of sodium chloride in solutions. The method also enables to measure and calculate the phase difference among each pixel of two samples. This makes it possible to generate a global measurement of the phase difference of the entire sensed region

Foucault test: shadowgram modeling from the physical theory for quantitative evaluations

The physical theory of the Foucault test has been investigated to represent the complex amplitude and irradiance of the shadowgram in terms of the wavefront error; however, most of the studies have limited the treatment for the particular case of nearly diffraction-limited optical devices (i.e., aberrations smaller than the wavelength). In this paper we discard this restriction, and in order to show a more precise interpretation from the physical theory we derive expressions for the complex amplitude and the irradiance over an optical device with larger aberrations. To the best of our knowledge, it is the first time an expression is obtained in closed form. As will be seen, the result of this derivation is obtained using some properties of the Hilbert transform that permit representing the irradiance in a simple form in terms of the partial derivatives of the wavefront error. Additionally, we briefly describe from this point of view a methodology for the quantitative analysis of the test

Real-time measurement of the average temperature profiles in liquid cooling using digital holographic interferometry

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. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE

Aproximación a la reconstrucción tomográfica óptica de objetos de fase suaves usando polinomios Chebyshev

En este artículo se presenta la reconstrucción de la imagen de la sección transversal de un objeto de fase usando técnicas de tomografía óptica, partiendo de la imagen de un interferograma sin portadora y un sistema óptico en configuración Mach-Zehnder. La reconstrucción se realiza usando polinomios Chebyshev como funciones base y el objeto de fase cumple las características de ser suave, continuo y radialmente simétrico

Fast flame temperature estimation using a point diffraction interferometer and non-negative least square method

Some of the interferometry methods proposed for flame temperature measurements from its projection could be complex and demand so much computing time. Assuming a circular symmetric and smooth flame temperature distribution, it is possible to use a linear combination of Gaussian functions with weights constrained to non-negative values

Phase Unwrapping using Chebyshev Polynomials

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 unwrapping using a regular mesh grid

Phase unwrapping is a key step in the fringe pattern analysis. Although there are many algorithms for recovering continuous phase from wrapped phase maps, many of them are computationaly heavy, even for smooth phase maps. The smoothness characteristics of a phase map allow the use of radial basis functions to model the unwrapped phase. This method helps to reduce the processing time when unwrapping the phase. The processing time can be reduced even more when the reconstruction does not take into account all the pixels of the phase map image. In this paper we describe an algorithm for phase unwrapping where the phase map is reconstructed from a subset of pixels of the phase image using radial basis functions (RBFs). The proposed method is compared with the algorithm based on the same radial basis functions (RBFs) but using all the phase image pixels

An alternative approach to the tomographic reconstruction of smooth refractive index distributions

Continuous, mathematically smooth Phase Objects with radial symmetry are reconstructed from cross sections of their refractive index distribution by a novel method, consisting of a linear combination of Gaussian basis functions, whose technical details are discussed. As an application example, this approach is used to get a fast and accurate estimation of the temperature distribution of an actual soldering tip

An alternative method for phase-unwrapping of interferometric data

In this paper we present a novel algorithm for phase unwrapping where only a subset of data from the wrapped phase map is used to reconstruct the unwrapped phase map as a linear combination of radial basis functions (RBF’s). For noisy phase maps this algorithm gives better results than three reference algorithms based on radial basis functions, Zernike polynomials and path dependent phase unwrapping strategies

Algoritmo para desenvolvimiento de fase unidimensional partiendo de un interferograma con frecuencia portadora implementado en labview

En el análisis de interferogramas, el desenvolvimiento de fase es una tarea primordial ya que al calcular la fase, ésta resulta estar envuelta en un mapa con un rango entre -π a π o bien, de 0 a 2π. Al contar con un mapa de fase envuelto no se tiene la certeza de la información que se observa en el sistema óptico, entonces es preciso desenvolver la fase. Este trabajo presenta la implementación en LabVIEW de un algoritmo de desenvolvimiento de fase unidimensional basado en el método de Takeda partiendo de un interferograma con frecuencia portadora obtenido del montaje de un interferómetro Mach-Zehnder. El método presenta las ventajas de ser más ágil en comparación con Matlab, y su implementación es muy sencilla