On the 20th of December 2013, The United Nations (UN) General Assembly 68th Session proclaimed 2015 as the International Year of Light and Light-based Technologies (IYL 2015). The proclamation of an International Year focusing on the light science and applications recognizes the importance of light in the society, which plays a vital role in our daily lives, being visible in a widespread number of different areas, as for instance, in technology, education, energy, art, agriculture, health, among many others. In this work, the members of the Image Processing Laboratory from the Universitat Autònoma de Barcelona (UAB), analyze the concept of readapting some experiments in optics -usually conducted in different courses at the UAB physics degree- into the artistic context of the MACBA (Museu d’Art Contemporani de Barcelona). This project, called SummerLight, takes place within the framework of the IYL, as part of the activities devised to promote the visibility of light. The readapted experiments are expected to teach and improve the knowledge of high school students with respect to different important physical phenomena related to the wave nature of light as polarization, interferences and diffraction. This study analyzes the suitability of the proposed experiments in terms of student optical skills improvement. In addition, its contextualization into an artistic scenario is also discussed.
Diffraction is an important phenomenon introduced to Physics university students in a subject of Fundamentals of
Optics. In addition, in the Physics Degree syllabus of the Universitat Autònoma de Barcelona, there is an elective subject
in Applied Optics. In this subject, diverse diffraction concepts are discussed in-depth from different points of view:
theory, experiments in the laboratory and computing exercises. In this work, we have focused on the process of teaching
Fraunhofer diffraction through laboratory training. Our approach involves students working in small groups. They visualize and acquire some important diffraction patterns with a CCD camera, such as those produced by a slit, a circular aperture or a grating. First, each group calibrates the CCD camera, that is to say, they obtain the relation between the distances in the diffraction plane in millimeters and in the computer screen in pixels. Afterwards, they measure the significant distances in the diffraction patterns and using the appropriate diffraction formalism, they calculate the size of the analyzed apertures. Concomitantly, students grasp the convolution theorem in the Fourier domain by analyzing the diffraction of 2-D gratings of elemental apertures. Finally, the learners use a specific software to simulate diffraction patterns of different apertures. They can control several parameters: shape, size and number of apertures, 1-D or 2-D gratings, wavelength, focal lens or pixel size.Therefore, the program allows them to reproduce the images obtained experimentally, and generate others by changingcertain parameters. This software has been created in our research group, and it is freely distributed to the students in order to help their learning of diffraction. We have observed that these hands on experiments help students to consolidate their theoretical knowledge of diffraction in a pedagogical and stimulating learning process.
We present a new technique for measuring ultraprecise absolute optical surfaces. The technique combines the lateral shearing method but using a Fizeau interferometer. It achieves faster reconstructions than with a deflectometric system and without the influence of the reference surface. The system is limited by the imprecision of the linear stage and those of the estimation of the curvature of the reference surface. Regarding the guidance errors, we propose a new method to estimate pitch and roll based on data redundancy analysis. Numerical simulation results of pitch-and-roll estimations are given for realistic errors. Reconstructions using the sequential lateral shearing are also provided achieving nanometer accuracy.
In this work, we present the design, optimization and implementation of dynamic Stokes polarimeters based on a single
Twisted Nematic Liquid Crystal (TN-LC) panel. TN-LC material enables both to introduce a retardance and to rotate the
polarization ellipse orientation. For this reason, a simple setup composed by a transmissive TN-LC panel and a polarizer
can be built, leading to a complete Stokes polarimeter. Variations of the initial setup are analyzed with the aim of
minimizing the noise propagation to the Stokes vector calculations. In particular, working out of normal incidence to the
TN-LC panel and working on TN-LC reflective mode. Moreover, we carry out an optimization of the polarization
analyzers used in each configuration. Finally, we implement the optimized polarimeters and some incident Stokes
vectors are measured, proving their correct operation. Results are compared with those provided by a commercial
polarimeter and so, the suitability of applying a TN-LC panel on polarimeters design is confirmed.
In this work, we conduct a thoroughly comparison between different Stokes polarimeters based on Liquid Crystal
Displays: polarimeters based on a single Twisted Nematic Liquid Crystal panel and on two Parallel Aligned Liquid
Crystal panels. We carry out an optimization of the different polarimetric systems in order to reduce the noise
propagation when measuring the polarization. In addition, we implement the three best optimized polarimeters. The
experimental results are provided and discussed.
We demonstrate that by performing an accurately optimization of a dynamic Stokes polarimeter based on a single
Twisted Nematic Liquid Crystal panel, we achieve results close to those obtained by polarimeters based on two Parallel
Aligned Liquid Crystal panels.
In this work, we present the design, optimization and experimental implementation of complete Stokes polarimeters
based on parallel aligned and twisted nematic liquid crystal displays. The liquid crystal elements are used as variable
retarders whose retardance depends on the addressed voltage. By including this type of anisotropic devices in the
polarimeter design we obtain some benefits when compared to mechanical polarimeters. For example, they allow to
avoid the corresponding uncertainty due to mechanical movement. In addition, among the different polarimeter
configurations provided by the polarimeter design, we have also applied an optimization procedure based on the
minimization of different mathematical indicators (as the condition number or the equally weighted variance) in order to
minimize the error amplification from the radiometric measurements to the solution. Finally, the optimized polarimeters
are experimentally implemented and tested. In the implementation process, the eigenvalues method (a rigorous
calibration procedure) is used.
Synchrotron radiation sources have become brighter in recent years. In order to profit all this brilliance,
optical surfaces of the beamlines must have slope errors below 1-2 microradians RMS. Thus, it is necessary to
have accurate and repeatable measurements of these surfaces (plane, elliptical, toroid, etc.). In this work, a
Fizeau interferometer is used for their characterization. The accuracy of the measurement is limited by quality
of the reference surfaces of the interferometer. Lateral shearing technique is applied in order to remove the
influence of the reference surfaces. This technique requires to use two or more images of the surface displaced
each other. Then, systematic errors of the linear stage (guidance and positioning errors) become the limit for
an accurate characterization. Different algorithms for the estimation and compensation of these systematic
errors have been developed. They are based on the two dimensional redundancy of the data obtained from
multiple measurements. In addition, algorithms to control the alignment of the setup have been developed and
implemented in a stand-alone application. As a result, once errors introduced by the stage are controlled, an
accurate characterization of the optical surfaces for beamlines is obtained. With this extended data analysis,
the accuracy of the mirror characterization can be improved with independence of the quality of the reference
optics of the interferometer.
Polarimetry is an optical technique currently used in many research fields as biomedicine, polarimetric metrology or
material characterization, where the knowledge of the state of polarization of light beams and the polarizing properties of
polarizing samples is required. As a consequence, in such as applications it is necessary to use polarimeters which by
means of radiomentric measurements, lead to the obtaining of some important polarimetric information.
As is known, polarimeters include a state of polarization detector (PSD), which is typically formed by combinations of
waveplates and polarizers. Then, intensity measurements corresponding to the projection of the analyzed state of
polarization upon different configurations of the PSD used, leads to the determination of the polarimetric properties of
light beams. Here, we have studied and optimized a polarimeter based on PSD system containing two electronically
variable retardance waveplates. The variable waveplates are based on the Liquid Crystal Display technology, allowing
the implementation of a complete polarimeter without mechanical movements.
The performance of synchrotron beamline optics is often limited by the accuracy in the figuring and finishing
of the optical surfaces. In consequence, a very sensitive and accurate characterization of the optics is required
during manufacturing and testing. Such characterization can only be done with instruments like long trace
profilometers or Fizeau interferometers. In the case of the Fizeau interferometer, the accuracy is mainly
limited by the quality of the reference surface. In this work, we propose a new method for improving the
accuracy of the surface reconstruction by using the lateral shearing technique. It consists on measuring the
sample surface several times, applying different displacements. By subtracting these measurements each other,
the error introduced by the reference surface can be removed and the profile of the sample mirror can be
reconstructed. Then, the accuracy of the reconstruction is limited by the imprecisions of the linear stage used
to shift the sample mirror. The positioning error is analyzed regarding the shearing transfer function and
the Natural Extension. Small displacements are more sensitive to the positioning error, not only because the
error is comparatively bigger, but also because the error using Natural Extension is bigger than using large
displacements. Using the proposed technique, a statistical analysis regarding the positioning error has been
performed. Its conclusion is that the accuracy in metrology of x-ray mirrors is improved by at least a factor of
18 compared to that achieved with the Fizeau interferometer and a standard λ/20 reference surface, giving a
reconstruction error lower than 1.8 nm peak to valley.
The unification of the new European studies under the framework of the Bologna process creates a new adaptation within the field of Physics this academic year 08/09 and in the coming years until 2010. An adjustment to the programs is required in order to migrate to the new European Credit Transfer System (ECTS), changing the credit from 10 to 25 hours. This adaptation is mandatory for the new students. However, the current students under the previous program have the opportunity to avoid these changes and to finish the degree with the old curricula. One of the characteristics of the Image Processing Laboratory (IPL) is the feedback between the laboratory researchers and the students. From this mutual collaboration several students have participated in various scientific research studies. In general, when a student is introduced into the research group routine, they found some differences between the degree laboratory courses and the research laboratory dynamics. This paper provides an overview of the experiences acquired and the results obtained by undergraduate students in recent works related to liquid crystal display (LCD) characterization and optimization, LCD uniformity analysis, polarimeter design, LCD temporal fluctuation effects or diffractive optics and surface metrology.