Dioptric power measurement is an essential part of the characterization and quality control of lens manufacturing. In this framework, a fairly simple and potentially cost-effective method for lens characterization by interferometric fringe evaluation is reported. This technique consists of acquiring images of straight and parallel fringes projected onto a planar screen through the lens to be tested and in the regions surrounding the lens. Upon phase evaluation procedures, two apparent three-dimensional shapes of the screen are obtained, namely, the background contour and the one visualized through the test lens. The lens power is obtained as a function of the ratio between the two shapes and the parameters of the optical setup. The fringe pattern evaluation was performed by four-stepping and phase unwrapping methods. The results obtained by this technique were compared with the ones obtained by a commercial focimeter in the measurement of unifocal and progressive power lenses.
In this paper we present a new approach for thermal lens analysis using a two-wavelength DSPI (Digital Speckle Pattern
Interferometry) setup for wavefront sensing. The employed geometry enables the sensor to detect wavefronts with small
phase differences and inherent aberrations found in induced lenses. The wavefronts was reconstructed by four-stepping
fringe evaluation and branch-cut unwrapping from fringes formed onto a diffusive glass. Real-time single-exposure
contour interferograms could be obtained in order to get discernible and low-spacial frequency contour fringes and obtain
low-noise measurements. In our experiments we studied the thermal lens effect in a 4% Er-doped CaO-Al2O3 glass
sample. The diode lasers were tuned to have a contour interval of around 120 μm. The incident pump power was
longitudinally and collinearly oriented with the probe beams. Each interferogram described a spherical-like wavefront.
Using the ABCD matrix formalism we obtained the induced lens dioptric power from the thermal effect for different
values of absorbed pump power.
We studied the shape measurement of semiconductor components by holography with photorefractive Bi12TiO20
crystal as holographic medium and two diode lasers emitting in the red region as light sources. By properly tuning
and aligning the lasers a synthetic wavelength was generated and the resulting holographic image of the studied
object appears modulated by cos2-contour fringes which correspond to the intersection of the object surface with
planes of constant elevation. The position of such planes as a function of the illuminating beam angle and the tuning
of the lasers was studied, as well as the fringe visibility. The fringe evaluation was performed by the four stepping
technique for phase mapping and through the branch-cut method for phase unwrapping. A damage in an integrated
circuit was analysed as well as the relief of a coin was measured, and a precision up to 10 μm was estimated.
A method for improving the accuracy of surface shape measurement by multiwavelength holography is presented. In our holographic setup, a Bi12TiO20 photorefractive crystal was the holographic recording medium, and a multimode diode laser emitting in the red region was the light source in a two-wave mixing scheme. On employing such lasers the resulting holographic image appears covered with interference fringes corresponding to the object relief, and the interferogram spatial frequency is proportional to the diode laser's free spectral range (FSR). Our method consists in increasing the effective free spectral range of the laser by positioning a Fabry-Perot étalon at the laser output for mode selection. As larger effective values of the laser FSR were achieved, higher-spatial-frequency interferograms were obtained and therefore more sensitive and accurate measurements were performed. The quantitative evaluation of the interferograms was made through the phase-stepping technique, and the phase map unwrapping was carried out through the cellular-automata method. For a given surface, shape measurements with different interferogram spatial frequencies were performed and compared with respect to measurement noise and visual inspection.
The application of multi-wavelength holography for surface shape measurement is presented. In our holographic setup a Bi12TiO20 (BTO) photorefractive crystal was the holographic recording medium and a multimode diode laser emitting in the red region was the light source in a two-wave mixing scheme. The holographic imaging with multimode lasers results in multiple holograms in the BTO. By employing such lasers the resulting holographic image appears covered of interference fringes corresponding to the object relief and the interferogram spatial frequency is proportional to the diode laser free spectral range (FSR). We used a Fabry-Perot etalon at the laser output for laser mode selection. Thus, larger effective values of the laser FSR were achieved, leading to higher-spatial frequency interferograms and therefore to more sensitive and accurate measurements. The quantitative evaluation of the interferograms was performed through the phase stepping technique (PST) and the phase map unwrapping was carried out through the Cellular-Automata method. For a given surface, shape measurements with different interferogram spatial frequencies were performed and compared, concerning measurement noise and visual inspection.
A novel method for surface profilometry by holography is presented. We used a diode laser emitting at many wavelengths simultaneously as the light source and a Bi12TiO20 (BTO) crystal as the holographic medium in single exposure processes. The employ of multi-wavelength, large free spectral range (FSR) lasers leads to holographic images covered of interference fringes corresponding to the contour lines of the studied surface. In order to obtain the relief of the studied surface, the fringe analysis was performed by the phase stepping technique (PST) and the phase unwrapping was carried out by the Cellular-automata method. We analysed the relief of a tilted flat metallic bar and a tooth prosthesis.
The crystal field environment of the Ce+3 dopant in LiSrAlF6 (LiSAF) crystals has been studied by the Electron Spin Resonance (ESR) spectroscopic technique. Ce was found in a highly anisotropic trigonal environment which suggests that it substitutes for the Sr site. Na+ ions operate as charge compensators to Ce+3 possessing nearby to Ce, Sr sites. The ground state electronic wavefunction and the energy diagram of Ce are discussed in view of our ESR results.
We describe the use of a self-stabilized setup for timeaveraged holographic interlerometry recording of a vibrating surface in a perturbed environment. The hologram is recorded with the 632.8-nm wavelength of an He-Ne laser on a Bi12TiO20 crystal. The performance of the setup is discussed and experimentally evaluated.
We describe the use of a self-stabilized setup for time-average holographic interferometry recording of a vibrating surface in a perturbated environment. The hologram is recorded with the 632.8 nm wavelength of an He-Ne laser on a Bi12TiO20 crystal. The performance of the setup is discussed and experimentally evaluated.