Karolina Macúchová

Optimizing of functional design parameters of kaleidoscopes

Imaging of surface textures requires many combinations of incident illumination angles and detector angles of view. Kaleidoscope is one of the means for measurement of bidirectional texture function of various sample surfaces. An optical system featuring the kaleidoscope is proposed in the paper. Optical parameters of such an imaging system are described and evaluated. We also discuss the optimization process of these parameters which influences the overall imaging performance of a kaleidoscope device. We provide the visualization of various kaleidoscope designs.

Software simulator for design and optimization of the kaleidoscopes for the surface reflectance measurement

Realistic reproduction of appearance of real-world materials by means of computer graphics requires accurate measurement and reconstruction of surface reflectance properties. We propose an interactive software simulation tool for modeling properties of a kaleidoscopic optical system for surface reflectance measurement. We use ray tracing to obtain fine grain simulation results corresponding to the resolution of a simulated image sensor and computing the reflections inside this system based on planar mirrors. We allow for a simulation of different geometric configurations of a kaleidoscope such as the number of mirrors, the length, and the taper angle. For accelerating the computation and delivering interactivity we use parallel processing of large groups of rays. Apart from the interactive mode our tool also features batch optimization suitable for automatic search for optimized kaleidoscope designs. We discuss the possibilities of the simulation and present some preliminary results obtained by using it in practice.

Simulation, Measurement and Spectral Analysis of Night Sky Light Background

Spectral measurements of the night sky provide important information about natural light sources and light pollution. Analysis of spectral data enables identification of interesting events occurring in the atmosphere. We describe the used method and the technical solution, as well as first obtained results. Photometric and spectral simulations of the night sky light were performed under laboratory conditions. The results were compared with measured data of the whole night sky with respect to location and timing. The outdoor measurements provided spectroscopic data for examining the light pollution and night sky light background.

Optomechanical design of rotary kaleidoscope for bidirectional texture function acquisition

Optical systems are traditionally used for accurate recording and measurement of the real worlds appearance. Present techniques allow us to form a computer-based virtual world, which is used in a variety of technical fields. The crucial issue for future applications of virtual reality is the fidelity of rendered images to real-world objects. This is strongly affected by the appearance of the rendered objects surfaces. Currently, the most applied method of describing a surfaces visual appearance of spatially nonuniform surfaces is bidirectional texture function (BTF). We have designed, optimized, built, and tested a unique portable instrument based on a rotary kaleidoscope principle for BTF acquisition in situ. To the best of our knowledge, such an instrument has never been used before to measure BTF of a surface. We enhanced a common static kaleidoscope by adding rotation, which allows us to get a larger number of images of the sample for more combinations of illumination directions and viewing directions. This results in a higher directional and spatial resolution of measured BTF data. In this paper, we focus on the optomechanical design of the rotary BTF measurement instrument and issues related to its alignment to keep the desired mechanical precision.

Geometric calibration of rotational kaleidoscopic instrument

The measurement of spatially varying surface reflectance is required for faithful reproduction of real world to allow for predictive look of computer generated images. One such proposed method uses a rotational kaleidoscopic imaging, where illumination and imaging paths are realized by subimages on kaleidoscopic mirrors and illumination is carried out by a DLP projector. We describe a novel geometric calibration method for a rotational kaleidoscope that is necessary to get aligned and accurate data from measurement. The calibration has two stages. The first stage mechanically adjusts the camera, the projector, and the autocollimator against the kaleidoscope mirrors. The second stage is based on the software. By random perturbation of camera and projector in corresponding mathematical model of the kaleidoscope we estimate better real positions of camera and projector in a physical setup, comparing the computed images from the software simulator and the acquired images from the physical setup.

Opto-mechanical design of vacuum laser resonator for the OSQAR experiment

This paper gives short overview of laser-based experiment OSQAR at CERN which is focused on search of axions and axion-like particles. The OSQAR experiment uses two experimental methods for axion search – measurement of the ultra-fine vacuum magnetic birefringence and a method based on the “Light shining through the wall” experiment. Because both experimental methods have reached its attainable limits of sensitivity we have focused on designing a vacuum laser resonator. The resonator will increase the number of convertible photons and their endurance time within the magnetic field. This paper presents an opto-mechanical design of a two component transportable vacuum laser resonator. Developed optical resonator mechanical design allows to be used as a 0.8 meter long prototype laser resonator for laboratory testing and after transportation and replacement of the mirrors it can be mounted on the LHC magnet in CERN to form a 20 meter long vacuum laser resonator.

Differential interferometer for measurement of displacement of laser resonator mirrors

This paper covers a description and a technique of a possible optical method of mode locking within a laser resonator. The measurement system is a part of instrumentation of laser-based experiment OSQAR at CERN. The OSQAR experiment aims at search of axions, axion-like particles and measuring of ultra-fine vacuum magnetic birefringence. It uses a laser resonator to enhance the coupling constant of hypothetical photon-to-axion conversion. The developed locking-in technique is based on differential interferometry. Signal obtained from the measurement provide crucial information for adaptive control of the locking-in of the resonator in real time. In this paper we propose several optical setups used for measurement and analysis of mutual position of the resonator mirrors. We have set up a differential interferometer under our laboratory conditions. We have done measurements with hemi-spherical cavity resonator detuned with piezo crystals. The measurement was set up in a single plane. Laser light was directed through half-wave retarder to a polarizing beam splitter and then converted to circular polarization by lambda/4 plates. After reflection at the mirrors, the beam is recombined in a beam splitter, sent to analyser and non-polarizing beam splitter and then inspected by two detectors with mutually perpendicular polarizers. The 90 degrees phase shift between the two arms allows precise analysis of a mutual distance change of the mirrors. Because our setup was sufficiently stable, we were able to measure the piezo constant and piezo hysteresis. The final goal is to adapt the first prototype to 23 m resonator and measure the displacement in two planes.

Recent progress in opto-mechanical design of cavity developed for the OSQAR experiment

Two optical methods are used in the laser-based experiment OSQAR at CERN for the search of axions and axion-like particles. The first method looks as light shining through the wall. The second one wants to measure the ultra-fine vacuum magnetic birefringence. Both methods have reached its attainable limits of sensitivity. Present work is focused on increasing the number of photons and their endurance time within the magnetic field using a laser cavity. Presented paper covers recent state of development of a prototype of a 1 meter long laser cavity which is the prerequisite of further development of the experiment.