Jana Harizanova

Compact electronic speckle pattern interferometer using a near infrared diode laser and a reflection holographic optical element

The complicated experimental set-ups required for existing electronic speckle pattern interferometers limit their application potential. To overcome the limitations we present a simple and very compact electronic speckle pattern interferometer. Our system does not use expensive and complicated optical elements. We used a near infrared reflection holographic optical element for the first time in an out-of-plane sensitive electronic speckle pattern interferometer operating with a near infrared diode laser. The use of a holographic optical element drastically reduces the number of optical elements; the final system only consists of a CCD camera, a HOE and a test object, with significant reductions in system costs and time spent aligning the system. Reflection holographic optical elements were recorded in HP-650 emulsions using a He?Ne laser. The hologram was reconstructed using a laser diode operating at 784?nm by swelling the emulsion. Current modulation of the laser diode was utilized to introduce the desired phase shifts for fringe analysis.

Pattern projection with a sinusoidal phase grating

The aim of this work is to study the diffractive properties of a sinusoidal phase grating for incorporation as a pattern projection element in a multisource and multicamera phase-shifting profilometric system. Two challenges should be overcome for successful operation of such a system, which are connected to inherent limitations of the phase-shifting algorithm—requirements for a sinusoidal fringe profile and for equal background and contrast of fringes in the recorded patterns. As a first task, we analyze the frequency content of the projected fringes in the Fresnel diffraction zone for parallel and divergent light illumination at different grating parameters and wavelengths. As a second task, we evaluate the systematical errors due to higher harmonics and multiwavelength illumination. Finally, operation of the four-wavelength profilometric system is simulated, and the error of the profilometric measurement evaluated. The results of test measurements are also presented.

Real time phase stepping pattern projection profilometry

A single-shot fringe projection profilometry system based on simultaneous projection of four phase-shifted sinusoidal fringe patterns generated at four different wavelengths is described. The system includes a fringe pattern generation module containing four blocks with four near-infrared diode lasers and a registration module with four CCD cameras. In order to simplify the technical solution and to avoid the stringent requirement for stability in the case of interferometric fringe generation, we study both theoretically and experimentally realization of the proposed system by using of a phase grating as well as a holographic optical element for reconstruction of two point sources. The results of the measurement of the relative and absolute coordinates of test objects for both types of diffraction gratings are presented.

Two-spacing projection phase stepping interferometry for 3D-surface measurements of large-scale objects

A precise interferometric method for three-dimensional shape measurements in a wide dynamic range with double symmetrical illumination of the objects is presented. The technique proposed is especially useful for remote, non-destructive in-situ measurements of art and archaeological objects. The method is based on projection two-spacing phase-stepping interferometry. The theoretical approach, experimental results as well as a sensitivity assessment of the measurements are discussed.

Relative and Absolute Coordinates Measurement by Phase-Stepping Laser Interferometry

Relative and absolute coordinates measurements of real objects by phase-stepping laser interferometry are presented. The method proposed is suitable for remote nondestructive testing and accurate measurement of real object such as machine’s parts, modules, constructions, as well as archaeological monuments and in biomedical investigations for spinal deformations measurements of human body, etc. Theoretical analysis for calculation of the coordinates from the measured phase difference in illumination of the objects with different phase-shifted interference patterns as well as uncertainty of the measurements are proposed. A good agreement with experimentally obtained results is achieved.

Two-wavelength and two-spacing projection interferometry for real objects contouring

The comparison between two-wavelength and two-spacing projection phase-stepping interferometry for real object contouring is presented. Single exposure reflection hologram with two-frequency generating temperature stabilized diode laser is realized. Theoretical approach, experimental results as well as the assessment of sensitivity and uncertainty of the measurements are discussed.

Pattern Projection with a Sinusoidal Phase Grating

The present work focuses on a sinusoidal phase grating as a pattern projection element in a phase-shifting profilometric system. Usage of the phase grating for fringe pattern generation under coherent illumination proposes several advantages as technical simplicity, high efficiency, minimization of the phase-shifting error, large focal depth and independence of the fringe pattern spatial period on the wavelength. The work considers the frequency content of the projected fringes in the Fresnel diffraction zone and gives the results of test measurements of relative 3D coordinates by means of a pattern projection system with a phase grating that is interferometrically recorded on a holographic plate. Implementation of sinusoidal phase gratings in a four-wavelength profilometric system with parallel recording of the phase-shifted patterns by a multi-camera system for real-time measurements of 3D coordinates of objects and scenes is discussed.

Projection Moire measurement of the deflection of composite plates subject to bird strike impact

For the new generation aircraft families, the use of fibre-reinforced plastics is considered for the leading edge of the wings. However, this leading edge is very prone to bird strike impact. This paper presents the use of the projection moire technique to measure the out-of-plane deflections of composite plates subject to bird strike. Very strict constraints with regard to: (i) high speed image acquisition, (ii) vibrations of the impact chamber, and (iii) projection and observation angles - complicated substantially the development of the set-up. Moreover, the high frame rates (12000 fps) required a very intensive illumination. In the optimized configuration, a specially designed grating with gradually changing period is projected by means of special Metal Hydride lamps through one of the side windows of the impact chamber onto the composite plate riveted in a steel frame. The digital high speed camera is mounted on the roof of the impact chamber and records through a mirror the object surface with the projected fringe pattern on it. Numerical routines based on Local Fourier Transform were developed to process the digital images, to extract the phase and the out-of-plane displacements. The phase evaluation is possible due to the carrier frequency nature of the projected moire pattern. This carrier frequency allows separation of the unwanted additive and multiplicative fringe pattern components in the frequency domain via the application of a proper mask. The numerical calculations were calibrated for the bird strike of an aluminium plate, where the plastic deformation could be checked after the test.

Real-time multicamera system for measurement of 3D coordinates by pattern projection

The report describes a real-time pattern-projection system for measurement of 3D coordinates with simultaneous illumination and recording of four phase-shifted fringe patterns which are projected at four different wavelengths and captured by four synchronized CCD cameras. This technical solution overcomes the main drawback of the temporal phase-shifting profilometry in which the pattern acquisition is made successively in time. The work considers the use of a sinusoidal phase grating as a projection element which is made by analysis of the frequency content of the projected fringes in the Fresnel diffraction zone and by test measurements of relative 3D coordinates that are performed with interferometrically recorded sinusoidal phase gratings on holographic plates. Finally, operation of a four-wavelength profilometric system with four spatially phase-shifted at &pgr;/2 sinusoidal phase gratings illuminated with four diode lasers at wavelengths 790 nm, 810 nm, 850 nm and 910 nm is simulated and the systematical error of the profilometric measurement is evaluated.

Testing of fibers reinforced composite vessel by fringes projection and speckle shear interferometry

Fringes projection and speckle shear interferometry are used for testing of subjected to cycling loading (pressure) composite vessel. As the sensitivity of the applied methods could vary in broad limits in comparison with the other interferometric techniques, the inspection is realized in a wide dynamic range. Two spacing phase stepping fringes projection interferometry is applied for absolute coordinate measurement. Derivatives of in-plane and out-of-the-plane components of the displacement vector over the object surface are obtained by lateral speckle shear interferometry in static loading (pressure). Non-linear mechanical response and fatigue of composite material are clearly detected after cyclic sinusoidal loading by macro measurement using lateral speckle shear interferometry. Fringes projection and speckle-shear interferometry are suitable for shape and normal displacements measurements in a wider dynamic range. The other advantage of the shown methods is connected with the possibility to realize compact and portable devices for in-situ inspection of investigated objects - machine parts and constructions.