Manuel Campos-García

Bio: Manuel Campos-García is an academic researcher from National Autonomous University of Mexico. The author has contributed to research in topics: Radius of curvature (optics) & Conical surface. The author has an hindex of 10, co-authored 72 publications receiving 433 citations. Previous affiliations of Manuel Campos-García include National Institute of Astrophysics, Optics and Electronics.

Null-screen testing of fast convex aspheric surfaces.

Abstract: A method for null-testing fast convex aspheric optical surfaces is presented The method consists of using a cylindrical screen with a set of lines drawn on it in such a way that its image, which is formed by reflection on a perfect surface, yields a perfect square grid Departures from this geometry are due to imperfections of the surface, allowing one to know if the surface is close to the design shape Tests conducted with a full hemisphere and with the parabolic surface of a lens show the feasibility of the method Numerical simulations show that it is possible to detect surface departures as small as 5 microm

Testing fast aspheric concave surfaces with a cylindrical null screen

Abstract: A noncontact test procedure to obtain the shape of fast concave surfaces is described. A cylindrical null screen with a curved grid drawn on it in such a way that its image, which is formed by reflection on a perfect concave surface, yields a perfect square grid is proposed. The cylindrical null screen design and the surface evaluation algorithm are presented. Experimental results for the testing of an elliptical mirror of 164 mm in diameter (f/0.232) are shown.

Quantitative evaluation of an off-axis parabolic mirror by using a tilted null screen.

Abstract: We report the testing of a fast off-axis surface based on the null screen principles. Here we design a tilted null screen with drop shaped spots drawn on it in such a way that its image, which is formed by reflection on the test surface, becomes an exact square array of circular spots if the surface is perfect. Any departure from this geometry is indicative of defects on the surface. Here the whole surface is tested at once. The test surface has a radius of curvature of r = 20.4 mm (F/0.206). The surface departures from the best surface fit are shown; in addition, we show that the errors in the surface shape are below 0.4 μm when the errors in the determination of the coordinates of the centroids of the reflected images are less than 1 pixel, and the errors in the coordinates of the spots of the null screen are less than 0.5 mm.

Testing fast aspheric convex surfaces with a linear array of sources.

Abstract: We describe a noncontact test procedure with which to obtain the shapes of fast convex surfaces. For this, an array of sources is positioned in a straight line and separated in such a way that the image by reflection on the surface consists of a set of equally spaced bright spots. By rotating the surface, we test different meridians such that, after 360°, the entire surface is measured. We present the source array design and the surface evaluation algorithm. We found that, to reduce numerical error in the evaluation of the shape of the surface, a numerical integration must be performed by a method that uses parabolic arcs instead of the traditional method that uses trapezoids. Through some numerical simulations we analyzed the accuracy of the method by introducing random displacements into the measured data. We found that to measure the quality of the surface with accuracy better than 5 μm, we have to measure the coordinates of the centroids on the image plane with an accuracy better than 0.5 pixel, and we to have measure the positions of the linear sources with an accuracy better than 0.5 mm. Experimental results for the testing of a carbon fiber convex sphere of 383.6-mm diameter (f/0.398) are shown.

Surface shape evaluation with a corneal topographer based on a conical null-screen with a novel radial point distribution

Abstract: In order to measure the shape of fast convex aspherics, such as the corneal surface of the human eye, we propose the design of a conical null-screen with a radial point distribution (spots similar to ellipses) drawn on it in such a way that its image, which is formed by reflection on the test surface, becomes an exact array of circular spots if the surface is perfect. Any departure from this geometry is indicative of defects on the evaluated surface. We present the target array design and the surface evaluation algorithm. The precision of the test is increased by performing an iterative process to calculate the surface normals, reducing the numerical errors during the integration. We show the applicability of the null-screen based topographer by testing a spherical calibration surface of 7.8 mm radius of curvature and 11 mm in diameter. Here we obtain an rms difference in sagitta between the evaluated surface and the best-fitting sphere less than 1 μm.

Software configurable optical test system: a computerized reverse Hartmann test

Abstract: A software configurable optical test system (SCOTS) based on the geometry of the fringe reflection or phase measuring deflectometry method was developed for rapidly, robustly, and accurately measuring large, highly aspherical shapes such as solar collectors and primary mirrors for astronomical telescopes. In addition to using phase shifting methods for data collection and reduction, we explore the test from the point view of performing traditional optical testing methods, such as Hartmann or Hartmann-Shack tests, in a reverse way. Using this concept, the slope data calculation and unwrapping in the test can also be done with centroiding and line-scanning methods. These concepts expand the test to work in more general situations where fringe illumination is not practical. Experimental results show that the test can be implemented without complex calibration for many applications by taking the geometric advantage of working near the center curvature of the test part. The results also show that the test has a large dynamic range, can achieve measurement accuracy comparable with interferometric methods, and can provide a good complement to interferometric tests in certain circumstances. A variation of this method is also useful for measuring refractive optics and optical systems. As such, SCOTS provides optical manufacturers with a new tool for performing quantitative full field system evaluation.

Elastomeric lenses with tunable astigmatism

Abstract: Microlenses fabricated using flexible elastomers can be tuned in focal length by application of controlled strain By varying the strain azimuthally, the lenses may be deformed asymmetrically such that aberrations may be controlled This approach is used to tune the astigmatism of the tunable lenses, and it is shown that the generated wavefront may be accurately controlled The lens presented here has an initial focal length of 326 mm and a tuning range of +23 mm for approximately 10% applied strain The range of directly tunable Zernike polynomials representing astigmatism is about 3 µm, while the secondary lens errors, which cannot be tuned directly, vary only by about 02 µm Hans Zappe and colleagues at the University of Freiburg in Germany have realized elastic lenses whose properties can be controlled by strain Small, tunable polymer lenses are of interest for micro-optical applications, for example, in miniaturized imaging systems The focal length of such a lens can be adjusted by an externally applied strain, as this changes the shape of the lens The researchers used eight mechanical anchors placed around the circumference of the lens to apply different strains at various lens positions This achieved a complex deformation pattern on the surface, which allowed control over not only the lens’ focal length, but also its astigmatism Controlling such lens aberrations is important for micro-optical devices that, unlike the multiple-lens arrays used in microscope objectives, use as few lenses as possible

A survey of methods for the evaluation of reflective solar concentrator optics

Abstract: The optical quality of concentrators has a direct impact on the thermal efficiency of concentrating solar power plants. There is a need to evaluate the quality of the mirrors before installation and during operation. A review of the optical characterization techniques that have been developed for solar concentrators is presented. A brief description of the operation and methodology of each technique is done. The strengths and possible vulnerabilities of the techniques are also discussed. A classification of the different techniques in families according to their underlying principles of operation is proposed. Finally an analysis of the available information about the accuracy and precision of the different methods is carried out.

Flexible geometrical calibration for fringe-reflection 3D measurement

Abstract: System geometrical calibration is a challenging task in fringe-reflection 3D measurement because the fringe displayed on the LCD screen does not lie within the camera's field of view. Commonly, a flat mirror with markers can accomplish system geometrical calibration. However, the position of the markers must be precisely located by photogrammetry in advance. In this Letter, we introduce a calibration method by use of a markerless flat mirror. Experiments in phase measuring deflectometry demonstrate that the proposed method is simple and flexible.