Digital Holographic Interferometry Method Research Articles

High-precision gaseous flame temperature field measurement based on quadriwave-lateral shearing interferometry

Quadriwave-lateral shearing interferometry (QLSI) has a broad utilization in quantitative phase imaging (QPI) for refraction-type objects due to its compact structure and stable performance against external disturbance. Here we propose to use the QLSI technique to image and measure the gaseous flame temperature field distribution in high precision. The quantitative phase image of an axisymmetric candle flame is firstly reconstructed from the wire-mesh-like QLSI interferogram, and then the three-dimensional temperature field distribution is calculated with the axisymmetric projection transform algorithm. Compared to the conventional digital holographic interferometry (DHI) based on Mach-Zehnder architecture, the proposed method possesses a high-precision measurement and better stability in disturbed environment, benefiting from the compact common-path structure of QLSI. The temperature measurement errors of the proposed QLSI method are ±5.0 K and ±5.3 K in the presence of airflow disturbance and mechanical vibration, respectively, while those of the DHI method are ±7.6 K and ±12.9 K, respectively.

Implementation of digital holographic interferometry for pulsed plasma studies

The study of low-temperature plasma generated in pulsed mode at atmospheric pressure was carried out. The purpose of the presented research is to develop a method of digital holographic interferometry for registration and evaluation of parameters of low-temperature plasma at atmospheric pressure in pulsed mode. This type of plasma is currently applied in medicine and biology. Thus, there is a need to control the exposure dose and plasma environment formation regimes. As plasma parameters, it can be considered its electron concentration which can be calculated through the estimation of the refractive index of plasma pulse in relation to unperturbed state. The plasma pulses were activated in Helium. The plasma pulse frequency was 5 kHz and its duration was 750 ns. During an investigation a laboratory set-up for recording holographic images of plasma pulses was developed. Holograms are acquired on a digital camera and a pulsed laser INNOLAS SpitLight Hybrid II at a wavelength of 532 nm with pulse duration of 10 ns is used as a source of coherent radiation. In order to record plasma pulses, the laser, plasma generator and digital camera were strictly synchronized to each other. During the experiment, a series of about 500 holograms were acquired, and the reconstruction of the phase of the object field was calculated. Analysis of the sequence of holograms allowed calculations of phase difference (interferograms) related to the refractive index of low-temperature pulsed plasma in Helium. It is known that low-temperature plasma leads to low phase delay which forms low phase contrast of the evaluated interferograms. For this purpose, we carried out preliminary experiments with plasma-arc that has similar temporary parameters, however, with a higher phase contrast of the interferograms. The paper presents experimental results obtained by studying the phase contrast of the refractive index of pure Helium, plasma-arc and plasma pulses in Helium. Thus, the effectiveness of both the experimental set-up and the method to evaluate the interferograms related to the refractive index of the plasma pulse was verified. The data obtained can then be used to estimate the electron concentration of the plasma. However, it needs to increase the sensitivity of the method in order to enhance phase contrast. Increase of sensitivity can be done by means of extension of the spectral range, for example, toward to infra-red.

Snap-shot topography measurement via dual-VCSEL and dual wavelength digital holographic interferometry

In this paper, we propose a dual-wavelength digital holographic interferometry method based on a compact dual vertical-cavity surface-emitting laser (VCSEL) source. The source simultaneously emits light from two highly stabilized coherent light sources with slightly different wavelengths. A highly stabilized and adjustable current source enables the application of digital holographic dual-wavelength techniques to measure the shape of an object with height steps of a few millimeters. The wavelength drift over 12 h over the entire measurement range, which was evaluated using a wavemeter, was smaller than 1 pm. In addition to the low measurement uncertainty at large height jumps, the dual-wavelength digital holographic system distinguishes itself by its robustness to environmental disturbances such as air turbulence, heat load, and/or mechanical vibrations. This is enabled via a fiber-based almost common-path single-shot digital holographic acquisition of the information of the two different wavelengths using angular multiplexing. The experimental setup and data evaluation are discussed, and we present measurements of non-cooperative objects with specular reflective and/or diffuse reflective surfaces having different colors.

Determination of Deformation Fields of Diffuse Objects by Phase-Shifting Digital Holographic Interferometry

A modification of the method of digital holographic interferometry for the determination of deformations of an object with a diffuse surface by comparing two complex wavefronts reflected from the object at its two different states is considered. The difference of the proposed method with classical digital holography methods is that digital holograms by which the images are reconstructed have complex values determined by the phase shift method (‘‘complex’’ hologram), while classical digital holograms have only real values. Besides, digital holograms are reconstructed with allowance for inhomogeneity of the reference beam, which improves the reconstruction quality. For this purpose, a tunable neutral optical filter is introduced into the reference arm of the optical scheme of the interferometer. The method is verified experimentally.

Measurement of mass diffusion coefficients of O2 in aviation fuel through digital holographic interferometry

The experimental apparatus to measure the mass diffusion coefficients of O2 in aviation fuel was constructed based on the digital holographic interferometry method. The theory of mass diffusion coefficient and interference image processing were introduced in detail. The accuracy of the experiment was verified by measuring the mass diffusion coefficient of 0.33 mol/L KCl in aqueous solution at 298.15 K. The mass diffusion coefficients of O2 in RP3 and RP5 aviation fuels were measured at temperature from 278.15 K to 333.15 K, and the Arrhenius equation was employed to fit the experimental data. In terms of the Stokes-Einstein equation, the viscosities of these two aviation fuels were tested to estimate the correlation among mass diffusion coefficient, viscosity and temperature. A uniform polynomial calculation correlation was proposed to predict the mass diffusion coefficients of O2 in both RP3 and RP5 aviation fuels, and its accuracy is considerably higher than that of the Stokes-Einstein equation.

Effect of gamma irradiation on the physical and structural properties of basalt fiber.

Digital holographic interferometry (DHI), X-ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR) and scanning electron microscopy (SEM) were used to study the effects of gamma irradiation on the physical and structural properties of basalt fibers. For this purpose, set samples of basalt fibers were subjected to different doses of gamma irradiation (3, 10, 25, and 40 kGy). The Mach-Zehnder interferometer was used to capture holographic patterns which are used then to determine the unwrapped phase. From the unwrapped phase distributions, the optical path difference within the irradiated basalt samples was determined. Thus, refractive indices, and birefringence of irradiated basalt fibers were determined at different irradiation doses using DHI method. XRD technique was used to investigate the effect of irradiation doses on the crystalline behavior of fibers. FTIR was performed to each of the basalt samples to evaluate the changes in the surface chemical properties due to radiation exposure doses. The morphology of irradiated fibers was examined using SEM. The results indicate that basalt fiber has a resistance to gamma radiation. There are no significant effects on the physical, structural and chemical properties were demonstrated of basalt fibers in the doses range of irradiation.

Голографический метод дефектоскопии преформ оптических волокон

The work is devoted to an experimental study of the digital holographic interferometry method for flaw detection of optical fiber preforms (preforms). Flaw detection of the production of optical fibers plays an important role. This article describes the process of digital holographic shooting and image processing of holograms. Based on the Leith–Upatnieks optical scheme, a holographic interferometer scheme has been developed, in which a hologram is recorded directly on a CCD array. A series of experiments on holographic interferometry of flaw detection of optical fiber blanks has been carried out. Holographic interferometry allows you to record objects in different states. Based on the experimental data, the possibilities of the method are studied and the possibility of its use is justified, its advantages over other analyzers of optical fiber preforms are also presented.

Monitoring of sedimentation of aqueous suspensions of fine quartz by method of digital holographic interferometry

The usage of the method of digital holographic interferometry (DHI) for the study of fine dispersed suspensions of inorganic substances in the process of their sedimentation was proposed. It is shown that during research of nanosuspensions with particle sizes less than 400 microns method of DHI allows to reveal changes of parameters with greater precision than method of dynamic light scattering (DLS).

Estimation of optical heterogeneity of samples in the process of developing nanoporous matrices from two-phase glass

In this paper the research of optical heterogeneity of nanoporous silicate matrices (NPM) by method of digital holographic interferometry (DHI) is presented.

Surface shape measurement by multi-illumination lensless Fourier transform digital holographic interferometry

This paper presents a multi-illumination lensless Fourier transform digital holographic interferometry method for surface shape measurement. In this method, the interference phases with different effective synthetic wavelengths are obtained by tilting the illumination angle several times, and all are wrapped. A Fourier-transform demodulation algorithm employing all these wrapped phases simultaneously is used to determine the object surface shape. No phase unwrapping procedure is required, and the shape information of each point is calculated independently, thereby offering great flexibility for measuring objects with discontinuities surface, such as holes, steps and gaps. Experimental results demonstrate the validity of the principle.

Research of phase changes in process of storage of fine dispersed aqueous suspensions of inorganic substances

In the work were proposed to use the method of digital holographic interferometry on the example of suspensions of fine dispersed silica, developed by different ways, for studying fine dispersed suspensions of inorganic substances in combination with the process of their sedimentation. A comparison of experimental results obtained by this method and by method of dynamic light scattering is presented. The high sensitivity of the interferometric method, particularly during assessing of changes of suspensions with nanosized particles is shown.

Temperature dependence of Kerr coefficient and quadratic polarized optical coefficient of a paraelectric Mn:Fe:KTN crystal

We measure temperature dependence on Kerr coefficient and quadratic polarized optical coefficient of a paraelectric Mn:Fe:KTN crystal simultaneously in this work, based on digital holographic interferometry (DHI). And the spatial distribution of the field-induced refractive index change can also be visualized and estimated by numerically retrieving sequential phase maps of Mn:Fe:KTN crystal from recording digital holograms in different states. The refractive indices decrease with increasing temperature and quadratic polarized optical coefficient is insensitive to temperature. The experimental results suggest that the DHI method presented here is highly applicable in both visualizing the temporal and spatial behavior of the internal electric field and accurately measuring electro-optic coefficient for electrooptical media.

Digital Holographic Interferometry of a Wide Spectral Range in the Systems of Nondestructive Testing of Dynamics of Micro- and Macrosystems

Modern digital holographic interferometry is used to study the objects of various nature and various spatial scales. In this case, a wide spectral range of coherent electromagnetic radiation from long-wavelength infrared to deep ultraviolet is used. In this work, we present the results of studying dynamic processes in construction materials by the methods of digital holographic interferometry using radiation with a wavelength of up to 9.3 μm. The holographic method for testing of microelectromechanical structures is also considered. The method of digital holographic interferometry, which uses an automated holographic microscope, is proposed to study microscopic biological objects.

Enhanced sensitivity digital holographic interferometry

Corona discharges are generally characterized by a low optical density whose detection is often near or under the limits of interferometric techniques. In this paper, we propose a method of digital holographic interferometry that enables detection with enhanced sensitivity. This sensitivity increase is obtained by post-processing the digital holographic recordings with a set of point-wise image operations. The procedure is described mathematically and illustrated experimentally. Examples are given for an opaque object and for DC corona discharges generated in the symmetrical point-plane geometry.