Precise Mirror Research Articles

Design and Calibration of Plane Mirror Setups for Mobile Robots with a 2D-Lidar.

Lidar sensors are widely used for environmental perception on autonomous robot vehicles (ARV). The field of view (FOV) of Lidar sensors can be reshaped by positioning plane mirrors in their vicinity. Mirror setups can especially improve the FOV for ground detection of ARVs with 2D-Lidar sensors. This paper presents an overview of several geometric designs and their strengths for certain vehicle types. Additionally, a new and easy-to-implement calibration procedure for setups of 2D-Lidar sensors with mirrors is presented to determine precise mirror orientations and positions, using a single flat calibration object with a pre-aligned simple fiducial marker. Measurement data from a prototype vehicle with a 2D-Lidar with a 2 m range using this new calibration procedure are presented. We show that the calibrated mirror orientations are accurate to less than 0.6° in this short range, which is a significant improvement over the orientation angles taken directly from the CAD. The accuracy of the point cloud data improved, and no significant decrease in distance noise was introduced. We deduced general guidelines for successful calibration setups using our method. In conclusion, a 2D-Lidar sensor and two plane mirrors calibrated with this method are a cost-effective and accurate way for robot engineers to improve the environmental perception of ARVs.

SiC ceramic mirror fabricated by additive manufacturing with material extrusion and laser cladding

As the aperture of the optical component increases, the integrated design of the silicon carbide optical component and the support structure will lead to a more complex structure of the silicon carbide optical component, which is difficult to achieve with traditional ceramic molding and sintering technology. In this work, a novel shaping method for the fabrication of reaction bonded silicon carbide ceramic substrate was investigated. Here, four kinds of mixture consisting of silicon carbide, carbon black powder, and organic binder with different solid loading were developed by varying the content of the lubricant paraffin wax (PW) and printed by material extrusion (MEX). The effects of solid loading on the rheological properties of mixtures, thermal expansion behavior, and morphology of the samples after debinding were studied. Similarly, two kinds of materials were prepared with silicon carbide to carbon black ratios of 50: 50 and 60: 40 under optimal solid loading, and their microstructure was analyzed and compared. The results show that reaction bonded silicon carbide ceramics with a flexural strength of 310.41 ± 39.32 MPa and a modulus of elasticity of 346.3 ± 22.80 GPa can be obtained by MEX and reactive sintering when the ratio of silicon carbide to carbon black is 60:40 and at an optimum solid loading (~60 vol%). Subsequently, the dense glass layer was prepared on the surface of 3D printed SiC by laser cladding. After polishing and plating with Ag film, it shows good reflection. In the range of 500–800 nm, the average reflectivity is higher than 97%. The laser cladding Si layer acts as a transition layer, which improves the wettability between the glass melt and the substrate and weakens the decomposition of SiC. This work provides a reference for the preparation of high precision, high strength, and high density SiC ceramic mirror by material extrusion and laser cladding.

Subject pro-drop and past-tense auxiliary clitics in South-Western Ukrainian

AbstractSouth-Western Ukrainian dialects have retained the option of auxiliary clitics in the formation of the past tense. At the same time, they have past-tense forms without auxiliary clitics as in Northern Ukrainian dialects, and in Standard Ukrainian based on South-Eastern dialects. A sample corpus study suggests that South-Western Ukrainian also shows a higher frequency of subjectpro-drop than Standard Ukrainian. The South-Western Ukrainian pattern presents the precise mirror image of the same two features in South-Eastern ‘Borderland’ Polish. Here, the dialect adopted the option of past-tense forms without auxiliary clitics, next to those with them as in Standard Polish. At the same time, it shows a higher frequency of non-pro-drop than Standard Polish. I argue that these matching facts are the result of long- standing language contact that worked simultaneously in two directions: the increase in the use of an existing dialectal Ukrainian pattern under Polish influence, as well as the increase in the use of an existing dialectal Polish pattern under Ukrainian influence. As a result, both dialects show the same variation between past-tense forms with auxiliary clitics and without them, and they have mutually converging tendencies in subjectpro-drop – the Ukrainian dialect adapting towards Polishpro-drop, and the Polish dialect towards Ukrainian non-pro- drop. The bi-directionality of influence in the SWU dialectal area, thus, goes beyond other, unidirectional language-contact scenarios.

Development of Fast and Precise Scan Mirror Mechanism for an Airborne Solar Telescope

We developed a scan mirror mechanism (SMM) that enable a slit-based spectrometer or spectropolarimeter to precisely and quickly map an astronomical object. The SMM, designed to be installed in the optical path preceding the entrance slit, tilts a folding mirror and then moves the reflected image laterally on the slit plane, thereby feeding a different one-dimensional image to be dispersed by the spectroscopic equipment. In general, the SMM is required to scan quickly and broadly while precisely placing the slit position across the field-of-view (FOV). These performances are highly in demand for near-future observations, such as studies on the magnetohydrodynamics of the photosphere and the chromosphere. Our SMM implements a closed-loop control system by installing electromagnetic actuators and gap-based capacitance sensors. Our optical test measurements confirmed that the SMM fulfils the following performance criteria: i) supreme scan-step uniformity (linearity of 0.08%) across the wide scan range (${\pm}$1005 arcsec), ii) high stability (3${\sigma}$ = 0.1 arcsec), where the angles are expressed in mechanical angle, and iii) fast stepping speed (26 ms). The excellent capability of the SMM will be demonstrated soon in actual use by installing the mechanism for a near-infrared spectropolarimeter onboard the balloon-borne solar observatory for the third launch, Sunrise III.

Copper electroforming replication process for soft x-ray mirrors.

We developed a copper electroforming replication (CER) process to fabricate precise ellipsoidal mirrors for soft x-ray focusing. Some applications of ellipsoidal mirrors in x-ray microscopy require that all components that are close to samples, including the mirrors, are made of non-magnetic materials. In this study, a non-magnetic copper ellipsoidal mirror was fabricated by replicating a figured and super-polished quartz glass mandrel using an electroforming technique. It was found that the CER process has a high replication accuracy of 8 nm. The focusing performance of the mirror was characterized using a soft x-ray free-electron laser with a photon energy of 100 eV. A small focus size of 370 × 400 nm2 was achieved with a high reflectivity of 65%.

3D-printed electroactive polymer force-actuator for large and high precise optical mirror applications

We describe a new development for a full 3D-printed-force actuator based on an advanced electroactive polymer (EAP) dedicated to large and live optical mirror applications, i.e., Live-Mirror Project (https://www.planets.life/live-mirror). The thin-film casting method was used to additively manufacture actuators, and we developed an integrating 3D printing technology to the EAP force-actuator production. Our 3D-printed actuator consists of the plasticized terpolymer layer (polyvinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene (PVDF-TrFE-CTFE) doped with diisononyl phthalate (DINP) plasticizer) sandwiched between two electrodes layers made of conductive terpolymer carbon black (CB) composite. The conductive CB layers were developed here to have a high electrical conductivity that can be used under significant voltage. We also made compatible blends with an actuator layer based on DINP polymer. Several fully 3D-printed EAP proof-of-concept actuator configurations were printed on a two-millimeters thick flat glass, i.e., an optical mirror surface. Its electromechanical performance was analyzed as a function of actuator volume, layer number, and electrical field intensity.

Micro-stress bonding analysis of high precision and lightweight mirrors.

We propose analysis methods for mirror bonding. The functional relationship between the shrinkage of the adhesive layer and the shape accuracy of the mirror is established numerically. By designing the structural form of the optical mounting and setting an appropriate stiffness ratio between the mirror and bonding position of the optical mounting, the theoretical surface shape accuracy change can be determined. Accordingly, the mirror is bonded, and the surface shape accuracy of the mirror after bonding is found to be 0.020λ. This approach is useful in mirror design applications that require rapid preparation and accuracy control.

General approach to precise deformable mirror control.

We develop a simple and effective control method for accurate control of deformable mirrors (DMs). For a desired DM surface profile and using batches of observed surface profile data, the proposed method adaptively determines both a DM model (influence matrix) and control actions that produce the desired surface profile with good accuracy. In the first iteration, the developed method estimates a DM influence matrix by solving a multivariable least-squares problem. This matrix is then used to compute the control actions by solving a constrained least-squares problem. Then, the computed actions are randomly perturbed and applied to the DM to generate a new batch of surface profile data. The new data batch is used to estimate a new influence matrix that is then used to re-compute control actions. This procedure is repeated until convergence is achieved. The method is experimentally tested on a Boston Micromachines DM with 140 micro-electronic-mechanical-system actuators. Our experimental results show that the developed control approach can achieve accurate correction despite significant DM nonlinearities. Using only a few control iterations, the developed method is able to produce a surface profile root-mean-square error that varies from 5 - 30 [nm] for most of the tested Zernike wave-front modes without using direct feedback control. These results can additionally be improved by using larger data batches and more iterations or by combining the developed approach with feedback control. Finally, as we experimentally demonstrate, the developed method can be used to estimate a DM model that can effectively be used for a single-step open-loop DM control.

Abelian mirror symmetry of mathcal{N} = (2, 2) boundary conditions

We evaluate half-indices of mathcal{N} = (2, 2) half-BPS boundary conditions in 3d mathcal{N} = 4 supersymmetric Abelian gauge theories. We confirm that the Neumann boundary condition is dual to the generic Dirichlet boundary condition for its mirror theory as the half-indices perfectly match with each other. We find that a naive mirror symmetry between the exceptional Dirichlet boundary conditions defining the Verma modules of the quantum Coulomb and Higgs branch algebras does not always hold. The triangular matrix obtained from the elliptic stable envelope describes the precise mirror transformation of a collection of half-indices for the exceptional Dirichlet boundary conditions.

Application of precise neutron focusing mirrors for neutron reflectometry: latest results and future prospects

Neutron reflectometry (NR) is a powerful tool for providing insight into the evolution of interfacial structures, for example via operando measurements for electrode-electrolyte interfaces, with a spatial resolution of nanometres. The time resolution of NR, which ranges from seconds to minutes depending on the reflection intensity, unfortunately remains low, particularly for small samples made of state-of-the-art materials even with the latest neutron reflectometers. To overcome this problem, a large-area focusing supermirror manufactured with ultra-precision machining has been employed to enhance the neutron flux at the sample, and a gain of approximately 100% in the neutron flux was achieved. Using this mirror, a reflectivity measurement was performed on a thin cathode film on an SrTiO3 substrate in contact with an electrolyte with a small area of 15× 15 mm. The reflectivity data obtained with the focusing mirror were consistent with those without the mirror, but the acquisition time was shortened to half that of the original, which is an important milestone for rapid measurements with a limited reciprocal space. Furthermore, a method for further upgrades that will reveal the structural evolution with a wide reciprocal space is proposed, by applying this mirror for multi-incident-angle neutron reflectometry.

A simple extended-cavity diode laser using a precision mirror mount.

We have developed an extended-cavity diode laser (ECDL) with a simple design by using a commercial precision mirror mount with minor modifications. Our design allows tuning of the external cavity configuration by tweaking the volume holographic grating without troublesome changes in the beam path of the laser output. The mode-hop-free tuning range of the presented ECDL is about 8 GHz with a linewidth of 475 kHz.

Implementation of Sensor Precision Mirror Rate using FPGA

The research contribution is increasing in the field of autonomous spacecraft. The major role contributes to the navigation methods for spacecraft. The intended control design is required precision mirror rate sensor (PMRS) to maintain positioning and stability of the satellite. One major drawback of the PMRS resides in the lock in effect, by which the sensor is not capable of sensing the rotation at low inertial angular rates. In the proposed work due to the uniqueness, it is able to sense the rotation even at the low inertial angular rates. The frequency control loop has been designed, it generates the resonance frequency using dither motor. The frequency control loop of the PMRS, is developed using a 32 bit MICROBLAZE soft core processor along with PID algorithm and same is executed using Xilinx Spartan 6 FPGA.

An Accurate Calibration Means for the Phase Measuring Deflectometry System.

Calibration is a critical step for the phase measuring deflectometry system. Existing calibration methods are mainly optimizing the calibration parameters with respect to the 2D re-projection error criterion. However, such a procedure cannot reduce metric errors in the practical application. Therefore, an accurate and practical calibration method is proposed. In which, conventional calibration means is first applied for the primary calibration. Then, a precise square planar mirror is used for the optimization of system calibration parameters. All the intrinsic and extrinsic parameters are considered as a global multi-objective optimization problem. Three metric error criteria are introduced to evaluate the 3D reconstruction accuracy of the reference mirror. Compared with classical calibration means, which apply the parameter optimization in 2D image space to minimize the re-projection errors, the proposed optimization approach is executed in 3D space directly. An experiment and comparison are conducted to verify that the proposed optimal calibration approach can effectively reduce the system deviation and to improve the system measurement accuracy.

CAOS line camera.

Proposed and demonstrated is the coded access optical sensor (CAOS) line camera, a one-dimensional or line version of the two-dimensional (2D) digital-micromirror-device (DMD)-based CAOS camera. The proposed line camera design includes a precise dual-axis mirror scanning galvo system incorporating feedback control that eliminates the need for mechanical motion of either the camera or the target. CAOS line scan imaging experiments using a white light source with two test targets are conducted and compared with non-scan 2D CAOS imaging. Specifically, a 2D DMD operated as both a full-frame and a line modulator is used to demonstrate both full-frame (${127} \times {45}$127×45 pixels) and line (127 pixels) scan CAOS imaging. Also demonstrated is an increase in field of view (FOV) of the camera unit using the galvo system with FOV increased by factors of 2.87 and 1.67 in the horizontal and vertical directions, respectively. In addition, proposed for future implementation is a CAOS line camera design that allows analog and hybrid analog-digital time-frequency CAOS-mode irradiance coding for realizing improved inter-pixel cross talk. The CAOS line camera versus a 2D image sensor camera is suited for broad-spectrum large area/FOV imaging applications where high linear dynamic range and low contrast recovery are critical challenges, such as in active illumination inspection of archeological and art works and industrial machine parts.

Development of space active optics for a whiffletree supported mirror.

The requirements of a lightweight primary mirror for large-aperture space telescopes include a precise mirror figure and high reliability. However, lightweight mirrors are easily affected by environmental disturbances, as they lack structural stability and rigidity. Active optics can be used to compensate for the gravity-induced deformation and correct low-order aberrations due to thermal changes and gravity relief during observing periods. Due to their complexity, active optics have been rarely used in space. To validate the technology of space active optics, an active optics system based on a passive, whiffletree-supported mirror is developed. During integration and testing on ground and under normal conditions in space, the surface accuracy is guaranteed by passive support. Within this hybrid support, the active optics system only serves to assist support. This paper focuses on the compatibility between a passive multisupporting system and active optics. We present the prototype of a 0.676m diameter passive supported lightweight mirror and active support with nine axial force actuators. The passive support includes a 9-point axial support and three A-frame lateral support. The active actuator distribution has been optimized with finite element analysis and its experimental performance characterized in representative conditions. The effectiveness of the hybrid passive-active support developed has been verified.

Surface‐Emitting Micro‐Mirror Superluminescent Diodes: Investigation of Tilt Accuracy Via Far‐Field Analysis

Far‐field characteristics of novel surface‐emitting micro‐mirror superluminescent diodes are investigated. The mirrors are fabricated by using thin film technology and an inductively coupled plasma etching process on wafer scale, suitable for mass production. Combining measurements and modeling results, the mirror tilt is estimated and the feasibility of good‐quality ≈45° mirrors is demonstrated. This approach offers an accuracy better than optical inspection with, e.g., scanning electron microscopy. In addition, our experiments revealed spurious ripples in the far‐field profiles with increasing tilt deviations, which finite‐difference time‐domain simulations identified as interference with back reflections. These results highlight the importance of tailored waveguides, high quality coatings, and precise mirror tilt to achieve maximal performance with surface‐emitting in‐plane semiconductor devices.

A New Precision Goniometer Mechanism for Direct Angle Measurement by a Rotary Encoder

In order to perform optical tests of an optical device such as a camera, a collimator system is needed which is aligned to a precision two axes rotary system (gimbal) where the optical device (Unit Under Test, UUT) is mounted. By the help of gimbal system, precision positioning of the UUT can be achieved and optical tests can be performed with a high accuracy. However, it is hard to position elevation axis accurately for relatively heavier UUT because of direct moment applied by UUT to the elevation axis of the gimbal system. Therefore, directly driven elevation axis is replaced by a goniometer system. Due to gear coupling clearance in goniometer systems, precision positioning is not achievable. In order to overcome this problem, a new mechanism, which is driven by a power screw, is used for the goniometer and virtual center of rotation is moved within the goniometer for direct angle measurement by a rotary encoder. Validation test is performed by autocollimator and precise mirror calibrators to check the accuracy of the new goniometer system.

Incoherent Gain-Assisted Ring Enhanced Gas Absorption Spectroscopy

A novel incoherent gain-assisted ring enhanced spectroscopy technique is presented in overcoming the need for precise optical alignment and high-reflectivity dielectric mirrors. A gain medium pumped below the lasing threshold is used to improve the ring finesse and, thus the interaction length. Two configurations are considered and compared. The first configuration is dual coupler ring with the source outside the ring and the gain medium inside the ring, while the second configuration is single coupler resonator with the gain medium acting as the source. The configurations are studied analytically and experimentally for different system parameters. The experimental results are obtained for a coupling ratio of 90/10. The broadband source is the amplified spontaneous emission of a semiconductor optical amplifier (SOA), while another SOA is used as the gain medium. Acetylene (C2H2) gas absorption is measured around 1540-nm wavelength. The output spectrum of the ring is measured using a 70-pm resolution. The interaction length is found to be enhanced by a factor of 9.35 and 44 in case of the dual coupler and a single coupler resonator, respectively, compared with the direct absorption of the gas cell.

NA62 RICH performance: measurement and optimization

Abstract The Ring Imaging Cherenkov detector of the NA62 experiment at CERN SPS was commissioned in 2014, but the optimal performance was achieved in 2016 after the precise mirror alignment with reconstructed tracks. The measurement and monitoring of basic performance parameters is discussed: ring radius resolution, ring centre resolution, single hit resolution and mean number of hits per ring. The performance is measured with 2016 data on the positron sample. Different contributions to the resolutions are calculated.

Breaking the speed-power-accuracy trade-off in current mirror with non-linear CCII feedback

Design of analog integrated circuit is a matter of trade-offs. Elementary blocks as simple as current mirrors must balance power, speed and accuracy as soon as they have to face dynamic inputs. In this paper, we propose a new structure of high-performance current mirror that overcomes the classical speed-power-accuracy limits. The structure combines a precise cascode current mirror with a custom low-power current conveyor used as a current mode non-linear feedback circuit. It is particularly suitable for fast multipolar current sources with high driving capabilities and small step response time over a large current dynamic. Design method and practical implementation are discussed in details. The circuit realized in AMS CMOS 0.18 μm technology at 1.8 V supply exhibits a large output current dynamic ranging from 160 μA to 2 m A, an average relative current copy error of 0.3% for worst-cases, a maximal settling time of 730 ns for full range step and a maximum quiescent power consumption of 142 μW.