Papers by Author: Ting Ming Huang

Abstract: A simple on-site transmittance measurement setup that is easy to move and install is proposed in this study. It is especially suitable for those cases when laboratory instruments are not applicable. Ordinarily, witness samples are measured since the uniformity is good enough inside the thin film coator and the size of the sample is proper for the facilities to measure. When the spot size of the measuring instrument is too large for the filter or the size of the test sample is too large to fit into the instrument. The proposed setup is shown to work well for this measurement. An application for this setup is also presented. The test target was a stripe filter, which has five band-pass thin films and nominal dimensions of 120 x 3.6 mm each film. Distance between neighboring films is 3.85 mm. The width of each film is so narrow and the size the stripe filter is large such that the traditional method for spectral transmittance is not applicable. The proposed measurement setup consists of a light source, integration sphere and spectrophotometer. The setup was installed inside a dark room. It shows that the setup can provide as accurate results as those data measured by an accreditated instrument. The difference between the present setup and accreditated instrument was found within 7% for high radiance. When the radiance of the incident light is low the accuracy decreases, which can be compensated by stronger light source. In addition, since the measurement spot size is estimated as 1.5 x 2.1 mm it can provide local transmittance data along the stripe thin film rather than a single data represented by the witness sample.

Abstract: The present study is aimed at investigating the thermal conduction characteristics of a spaceborn sensor experimentally and computationally. The experimental measurement has been carried out in a high vacuum chamber with twenty selected thermal couples attached to the sensor module. The detailed internal thermal control design, material for heat release, temperature limit, and control logic of the sensor assembly have been described in the study. The total thermal resistance for the sensor has been evaluated from the experimental results of the steady state temperature distributions under a heat power of 5.5 W and the sensor heater power modulation has been obtained to keep the PT1000 within the accepted temperature range. Under the assumed temperature boundary conditions, the measured thermal resistances and the modulated sensor heater power, the maximum PT1000 temperature distribution is found to be 25.26 °C ± 3.44 °C with the finite element analysis. Heat loss has been evaluated for the invar mount of the sensor module. In addition, the overall orbit peak and average heater powers needed are 4.61 W and 1.61 W respectively.

Abstract: Corrector lens assembly is used to expand the field of view of a Cassegrain Telescope. There are usually three to five lenses in it. For the assembly of such a kind of high precision optics, decenter and tilt of each optical component and air space between components are key issues to be qualified. In the present study, four lenses were designed. Individual control of centering of the component and air space were achieved by assembling the component into a precision machined subcell. The lens positions were defined by precision spacers according to the designed values. To compensate various thermal expansions of glass and metal, elastomer material was used. Considering the deviation of manufacturing from design data, manufactured data were put into optical software for re-optimization, and air spaces between lenses were obtained. This gives excellent accuracy at low cost. Base on present lens mounting design and lens manufacturing quality, centering error was eliminated by lateral adjustment, which leaded to a good alignment. In this paper, the method for aligning the optics with the barrel assembly is presented and centering error measured by a double autocollimator is listed. In addition, test results of thermal cycling and vibration tests on the corrector lens assembly are discussed.

Abstract: Optomechanical analysis and design approaches for development of large mirror mount are presented in this article. The relationship between mirror optical aberration and gravity effect is studied for difference mirror mount designs. A detailed structural analysis of mirror mount design using finite element model combined with Zernike polynomials fitting is found successfully to predict optical aberration in the Cassegrain optical system.

Abstract: The telescope primary mirror Isostatic Mount (ISM) design is an important issue for optical performance. The ISM bonding position will affect the telescope performance. The primary mirror reflection surface is parallel with gravity force during telescope alignment process. Thus, the distance between ISM geometry center and primary mirror center of gravity will lead mirror surface deformation. The ISM mounting mainly aberration is astigmatism at mirror surface. This study is applied Finite Element (FEM) simulate mirror surface deformation and using Zernike polynomial fitting the mirror surface aberration. The simulation result show the ISM bonding at mirror neutral plane the aberration will minimum at 1G gravity. The ISM bonding position errors also affect aberration distribution.

Abstract: Radius of curvature is one of the key parameters of optical components. A variety of methods have been developed for this measurement. This paper describes a novel way, named “CMM spherometry by probe compensation”, to measure the radius of curvature of optical surfaces by coordinate measuring machine (CMM). The measurement combines CMM measurement and iteration calculation scheme is presented. The measurement results of CMM and the trace samples are compared. The effect of temperature compensation is discussed.

Abstract: The present study is aimed at investigating the effect of acid etching durations on the surface roughness and birefringence of lightweight mirrors made of ZERODUR® glass ceramic. Four acid etching durations (15, 20, 25 and 30 min) have been chosen at a fixed concentration. By using the photoelasticity, surface profiler and laser microscope, the results before and after acid etching have been obtained. It is found the maximum value of the retardation for the polished lightweight ZERODUR® mirror is up to 30 nm. In addition, residual stresses induced by the grinding process with an average grain size of 149 μm are relived after removing ZERODUR® material of a thickness of 60 μm.

Abstract: This article reports an approach of light-weighted mirror design and analysis to increase the weight reduction ratio and improve optical performance based on the finite element method and opto-mechanical analysis. The approach is to represent mirror surface deformation derived from finite element analysis (FEA) by Zernike polynomials, such that the impact of deformation on optical system performance can be evaluated by the optical design and analysis program. The experimental modal analysis was also performed to validate the FEA results. The numerical result shows that the light-weighted primary mirror of Cassegrain telescope is obtained by this approach and predicted deformation fulfills the requirements of optical design.

Abstract: This article reports an accurate analysis approach of finite element modeling and optical modeling. It has been used for design and analysis of many opto-mechanical systems such as large telescopes and laser systems. The approach is to represent mirror surface deformation derived from finite element analysis (FEA) by Zernike polynomials, such that the impact of deformation on optical system performance can be evaluated by optical design and analysis program. The methodology of shell-based and solid-based finite element modeling and the comparison of their results have been described in this paper. The result shows that the deformation of the light-weighted mirror designed by this approach fulfills the requirements of optical design. The simulation results of shell based FE model are in good agreement with those of solid based FE model.