Polarization Holography with liquid crystals polymers and applications

Conference (2012, December 10)

Liquid Crystals Polymers are birefringent molecules locally orientable. By recording the polarization pattern due to the overlap of differently polarized beams on LCP, space-variant retarders are realized ... [more ▼]

Liquid Crystals Polymers are birefringent molecules locally orientable. By recording the polarization pattern due to the overlap of differently polarized beams on LCP, space-variant retarders are realized. We present two applications polarization holography and coronagraphy [less ▲]

Carrier and aberrations removal in interferometric fringe projection profilometry

in Gorecki, Christophe; Asundi, Anand K.; Osten, Wolfgang (Eds.) Optical Micro- and Nanometrology IV (SPIE proceedings vol.8430) (2012, April 17)

A profilometer which takes advantage of polarization states splitting technique and monochromatic light projection method as a way to overcome ambient lighting for in-situ measurement is under development ... [more ▼]

A profilometer which takes advantage of polarization states splitting technique and monochromatic light projection method as a way to overcome ambient lighting for in-situ measurement is under development [1, 2]. Because of the Savart plate which refracts two out of axis beams, the device suffers from aberrations (mostly coma and astigmatism). These aberrations affect the quality of the sinusoidal fringe pattern. In fringe projection profilometry, the unwrapped phase distribution map contains the sum of the object’s shape-related phase and carrier-fringe-related phase. In order to extract the 3D shape of the object, the carrier phase has to be removed [3, 4]. An easy way to remove both the fringe carrier and the aberrations of the optical system is to measure the phases of the test object and to measure the phase of a reference plane with the same set up and to subtract both phase maps. This time consuming technique is suitable for laboratory but not for industry. We propose a method to numerically remove both the fringe carrier and the aberrations. A first reference phase of a calibration plane is evaluated knowing the position of the different elements in the set up and the orientation of the fringes. Then a fitting of the phase map by Zernike polynomials is computed [5]. As the triangulation parameters are known during the calibration, the computation of Zernike coefficients has only to be made once. The wavefront error can be adjusted by a scale factor which depends on the position of the test object. [less ▲]

Polarization measurement with space-variant retarders in liquid crystal polymers

Conference (2011, August)

Polarization measurement with space-variant retarders in liquid crystal polymers

in SPIE proceedings 8160, SPIE Optics +Photonics 2011 San Diego (2011)

We present a real-time polarization measurement method with a space-variant phase retarder in liquid crystal polymers. This retarder presents a continuous and periodical variation of its optical axis ... [more ▼]

We present a real-time polarization measurement method with a space-variant phase retarder in liquid crystal polymers. This retarder presents a continuous and periodical variation of its optical axis orientation. The method computes the Stokes parameters of an incident beam by studying the intensity distribution after the retarder and a linear polarizer. This paper contains the mathematical modelization, the numerical simulation, the description of the experimental setup, the results for several completely polarized beams and the future developments of this method. [less ▲]

Application of shearography to crack detection in concrete structures subjected to traffic loading

in Armando Albertazzi, Armando Jr.; Kaufmann, Guillermo H. (Eds.) Speckle 2010: Optical Metrology (2010, September 13)

Early detection of defects in concrete structures, such as bridges or dams, is essential to optimize the maintenance of civil engineering facilities. Optical methods constitute non-destructive means of ... [more ▼]

Early detection of defects in concrete structures, such as bridges or dams, is essential to optimize the maintenance of civil engineering facilities. Optical methods constitute non-destructive means of control and measurement but they are generally confined in laboratories where both the setup and environnement are controlled. The method of shearography is especially well adapted to detect damages due to both its capacity to distinctly visualize strain concentration zones and its robustness. The experimental set-up is relatively compact, which enables to examine an extensive surface area by simply moving the shearographic head. In this paper, the application of this methodology for the detection of cracks is presented on concrete samples and circulated outside concrete structures. Due to its sensitivity to strain concentration, shearography is able to detect structural cracks, even when they were not through-cracks. Operational implementation is made on two circulated structures with experts in manual cracks detection. No stimulation device is used. In the first structure, cracks are detected on the bridge deck and on the bridge abutment. In the second structure, cracks on the intrados of the bridge deck are detected and also beginning of cracks which have not been detected by the visual inspection. Different areas are scanned and the results are in agreement with the visual inspection. This technique enables detecting cracks on structures subjected to traffic load. The natural loading of an engineering structure, i.e. the rolling traffic it bears, proves well suited for cracks detection by means of shearography, provided traffic patterns are regular enough. [less ▲]

Comparison of Spectral Colorimetric Measurements vs. Color Pictures in Dermatology

Poster (2010, April 13)

We studied scars and wounds depths and surfaces thanks to our interferometric fringes projector 3D scanner1, 2. Color information of a wound indicates its deterioration level. That’s why the visual color ... [more ▼]

We studied scars and wounds depths and surfaces thanks to our interferometric fringes projector 3D scanner1, 2. Color information of a wound indicates its deterioration level. That’s why the visual color restitution, as realistic as possible, is a highly important parameter. Firstly our acquired 3D pictures were color mapped with an image recorded by a RGB camera. The results were not efficient enough. In order to improve our technique and provide more precise information, we add a spectral characterization to the set-up. Before adding the spectral information and a realistic color mapping to the 3D measurements, we evaluate the performances of colorimetric measurements. The tests have been made on mice with scars on their back. [less ▲]

Contrer les effets du manque de lumière : La luminothérapie

Conference given outside the academic context (2009)

Utilisation d’une lame de Savart pour un système de projection de franges interférométriques pour la mesure de forme 3D

Conference (2009, November 18)

Non-contact optical measurement methods are essential tools in many industrial domain. Hololab developed an original out of plane, in line and almost common path interferometer based on polarization ... [more ▼]

Non-contact optical measurement methods are essential tools in many industrial domain. Hololab developed an original out of plane, in line and almost common path interferometer based on polarization states separation using a coated prism for fringes projection. This setup has proven efficient in the field of arts and archaeology but does not meet the demands of the industrial world. Above the acquisition speed and the post treatment process, one of the disadvantages comes from the sensitivity of the system to the environment. To overcome this disadvantage, the coated prism is substituted by a Savart plate. This device has already been used in another field of optical metrology as a shearing device. Many advantages of the prism substitution are discussed and recorded fringes patterns will be shown. [less ▲]