In this work, a specific procedure to measure the thickness of aluminum thin films by interferogram analysis is described. Six interferograms correspond to the image of the aluminum thin film superimposed with interference fringes are obtained from a Michelson-type interferential microscope. A six-frame phase shift algorithm is used to demodulate the optical phase. The measured phase is proportional to the height variation between the thin film wafer and the substrate. Finally, the obtained 3D height map permits us measure the thickness of the sample over an area of 1024 μm × 1280 μm.
In this work, we deduce explicit conditions to design phase shifting algorithms (PSAs) in order to suppress errors in phase measurement, the double-frequency ripple distortion and the spurious piston. These errors arise when non-uniform phase-shifting interferograms are processed with conventional PSAs which assume uniform phase shifts. By modeling the non-uniform phase shifts as a polynomial of the unperturbed phase shift value !0, we show that the conditions for eliminating those errors are associated to the m-th derivative of the PSA's frequency transfer function (FTF). Thus, we propose an approach to design robust algorithms based on the FTF formalism, and we present a ready-to-apply eight-frame PSA. Finally, our conclusions are supported by computer simulations.
We propose a vision-based position sensor based on Digital Holography (DH) for in-plane and out-of-plane displacements measurement of a patterned plate with sub-pixel resolutions. DH is a lensless imaging principle using solid-state camera and/or spatial light modulators (SLM). Object scenes are generated or reconstructed numerically through wave propagation computations applied to a diffracted optical field recorded as an interferogram. The application of visual positioning to manipulation tasks in micro-robotics requires high accuracy and wide ranges of displacements that, unfortunately, are limited by finite depth-of-focus and fixed working distance of refractive imaging systems. Recently, we demonstrated that DH allows in-plane positioning of mobile targets ensuring nanometer resolutions at diverse working distances within a continuous range of more than 15 centimeters. By recording a set of digital holograms of a pseudo-periodic pattern fixed onto a moving target, images in phase and in intensity are restored by numerical reconstruction using Angular Spectrum Propagation methods by adjusting the reconstruction distance. A last step consists in performing a direct phase measurements of periodic pattern to reach nanometer resolutions. Three 2DFFT are required at minimum to extract the pattern position, which is time consuming if several hundred of holograms are recorded. We explore a new approach that consists to restore in-plane / out-of-plane position directly from the 2DFFT of the digital hologram without any need for image restitution. The proposed vision-based position sensor combines a 10 Mp CMOS camera and a SLM in order to perform a fine control of the interferometer reference arm.
We describe the control of a piezoelectric device (PZT), mounted in an interferential microscope (IM) to introduce phase steps by mean of modifications light optical path, which is reflected from a sample surface. Both the piezoelectric control as the interferogram acquisitions from the interferometry system are made in a program designed in LabVIEW®. The program gives a stepped voltage by means PZT controller to a piezoelectric; causing deformation of the piezoelectric which in turn produces a shift in the surface mounted over it, resulting in a shift in the fringes pattern, besides the program controls a camera for acquiring an image at each voltage change. We use image processing to measure the displacement of the fringes finding out the position of the pixels which have a maximum of intensity, the first interferogram is set as a reference, in the following images the position of the pixel higher intensity is moving to fill the following pixel position with major intensity pixel of reference interferogram. Between two consecutive maximum and minimum of interference, the phase difference is 2π, then we can obtain the phase-shifting for each voltage change as well as the voltage needed to introduce a 2π phase-shifting in the fringe pattern, and finally obtain interferograms with a constant phase-shifting to reconstruct surface shape of thin films.
The characterization of the superficial topography of a thin film, obtained from an interferometer installed in our Optics Laboratory, is done using bi-dimensional images of its surface overlaid with interference fringes (interferogram1). These images differ among them only by a constant variation of the optical phase2. The total number of images to acquire depends on the image processing algorithm to apply; this algorithm allows to determine the value of the phase introduced by the surface form.
In this work, it is shown a panoramically view of advances and works on fundamental optical technology developed and Physics
Section at Pontificia Universidad Católica del Perú PUCP in Lima Peru. This includes works in, precision optics manufacturing,
optical testing, and optical design and simulation and also in optical thin film evaporation and its design techniques
It is shown how undergraduate Physics students were introduced to spectrographs optics through laboratory sessions and
computer simulations. Simulation and evaluation of two equivalent spectrographs corresponding to a real commercial
spectrograph were performed. Evaluation of the real spectrograph was also performed. A comparative work on
spectrographs linear dispersion and their resolution was also performed.
In this work we use an experimental set-up implemented in the Optical Physics Laboratory of PUCP, in order to study and to measure the roughness of different surfaces. The surfaces have different finishing obtained in different mechanic process (milling, turning, etc). The measurement method is based on a two-dimensional scan of scattered light from a rough metal surface illuminated by laser light. The light is scattered as speckle pattern and it is captured by the CCD of a digital camera in two different configurations, with and without an imaging lens and under different angles of illumination. Using two-dimensional Fast Fourier Transform it has been possible to compute the angular correlation between speckle pattern images and find out the relationship between surface roughness and speckle patterns decorrelation for different metal surface finishing.
In this work we use an experimental setup implemented in the Optical Physics Laboratory of PUCP, in order to study and to measure the roughness of surfaces with different surface finishing as milling, turning, etc. The measurement method is based on a two-dimensional scan of scattered light like from rough metal surface when the surface is illuminated by laser light. The light is scattered likes speckle in all space and arrives onto the CCD of a digital camera. The speckle images of rough surfaces are captured at different angles of illumination. We have analyzed the dependence between the structure of speckle and the surface roughness. Using two-dimensional Fast Fourier Transform it has been possible to compute the correlation between speckle pattern images and find out the relationship between surface roughness and speckle patterns decorrelation for different metal surface finishing.
We present an alternative development of very cheap sensors utilizing plastic optical fibers and diode lasers extracted from laser pointers. We have applied these sensors to perform measurements of displacement and distance without physical contact. The development of these sensors started with the characterization and control of these semiconductor lasers. We have achieved to control various diode lasers by means of a current controller, specially designed for this application. In this work, we show two different sensor configurations, getting a measurement range between 1 and 3 mm with microns resolution.
We performed a study of temporal coherence of a commercial He-Ne laser in conditions of thermic instability through calculations based on interference pattern digital images helping by direct measurements of its output power and by temperature and polarization monitoring. This study is based on the variation of the complex degree of coherence with the optical path difference between two laser beams, obtained with the help of an experimental setup based on a Michelson interferometer with collimated light. We show the perturbative effect of the thermic instability on the modal composition and coherence of radiation. We had characterized the laser determining its modal structure and coherence length.
A cheap piezoelectrically driven mirror can be easily constructed in the laboratory. It can be located in one arm of a DSPI interferometer in order to introduce a controlled phase step. A procedure to calibrate this device is shown, that is based on the evaluation of the fringes obtained with the interferometer. To evaluate the performance of the calibrated device, the phase map of a simulated plane object is calculated, using the four-step algorithm for the images of a speckle interferogram.
In this work, it is present a spherometer based in grating projection techniques and phase evaluation. The optical setup consists in a projector with a Ronchi ruling and a CCD camera interface d with an image processor. The CCD camera registers the images of the fringe-pattern as modulated by the object curvature and purposely-developed software digitally processes these images. The object profile is reconstructed using phase evaluation methods: particularly, were used the fast Fourier transform algorithm and phase stepping algorithms, With the resulting values and using the sagitta calculation the average radius of curvature can be evaluated in any point on the object surface.
This work shows characterization methods for laser pointers as whole system sand also for semiconductor lasers. We started developing a current controller and a power light meter designed and calibrated for this type of work. Characteristic curves as optical power output versus forward current and forward current versus forward voltage and also related characteristic parameters as threshold current are obtained. In addition, far field radiation patterns with their angles of divergence, the astigmatic distance are found. It is intended that these devices can be used for optics and optoelectronics education as well as for the development of measurement and communications systems based in semiconductor lasers.
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