The slit diaphragm is a useful type of flexure for producing small rotations or translations. This type of flexure is easily fabricated using modern technique such as electro-discharge machining, and provides a convenient solution for certain types of precision motion problems. There are two types of slit diaphragms used in optomechanics: a two axis gimbal for rotation and a linear flexure for translation. Closed form solutions are discussed for determining rotational and radial stiffness of the two axis gimbal slit diaphragm flexure. Similar equations are given for finding the linear and radial stiffness of the linear translation slit diaphragm flexure. A design example of a focus mechanism employing a pair of linear translation slit diaphragm flexures is discussed.
The airborne infrared imager (AIRI) is a dual-band IR sensor designed to study air defense issues while wing mounted in a pod. The sensor consists of an optical bench attached to a two- axis inertially stabilized gimbal structure in elevation and azimuth. The gimbal assembly operates within an 18-inch diameter globe while meeting strict pointing and tracking requirements. Design conditions for the assembly include operational and nonoperational inertial, thermal, and dynamic loads. Primary design efforts centered on limiting the line-of- sight jitter of the optical system to 50 (mu) rad under the operating environment. An MSC/NASTRAN finite element model was developed for structural response predictions and correlated to experimental data. Design changes were aided by MSC/NASTRAN's optimization routine with the goal of maximizing the fundamental frequency of the gimbal assembly. The final structural design resultsed in a first natural frequency of 79 Hz using a titanium azimuthal gimbal, a stainless steel elevation gimbal, and an aluminum optical bench which met the design and performance requirements.
A two axis optical gimbal mechanism for aligning 1 meter diameter telescope primaries and test flat mirrors at temperatures from 300 to 4.2 K was constructed for use in the SIRTF Telescope Test Facility (STTF). This mechanism consists of an aluminum frame, pivoting on a monoball bearing, and driven in tip and tilt by tungsten di-sulfide lubricated lead screws with external drive motors. Flexures decouple the optical support frame from stresses generated by differential rates of cooling. A second set of flexures decouples the mirror mechanically and thermally from distortion in the gimbal mechanism. The mechanism provides sub arc-second resolution in either axis, while limiting the heat leak to less than 100 mW at 4.2 K. Linear variable differential tranformers are used at temperatures from 300 to 4.2 K to measure a home position. The STTF and gimbal are presently operational, and have been used in two separate interferometric measurements of a 0.5 meter, f 4.0 beryllium spherical mirror at 6 K. The gimbal will be used in the interferometric testing of a beryllium telescope primary mirror from the Infrared Technology Testbed, for the Space Infrared Telescope Facility at JPL.
The final mechanical structure of the large binocular telescope (LBT) has an innovative design in order to achieve the strict scientific and technical requirements. Some of the most critical subassemblies of the l
The goal of polymeric fiber post-treatment is to achieve--under reproducible, nontransient conditions--significant enhancement of the mechanical properties of drawn fiber over those of undrawn fiber. Mechanical property enhancement is closely tied to macroscale orientation imparted to the monofilament through a combination of heat and draw over a short period of time. Drawing is difficult to characterize because the effective draw ratio, (lambda) , varies as a function of time before it may reach a steady-state value. As a result, the monofilament line may break or develop nonuniform mechanical properties before the limiting regime is reached. A pilot device has been designed and built to characterize and control the vital parameters associated with monofilament post-treatment in order to study the conditions which lead to production of superior fiber product. This monofilament post-treatment device incorporates real-time computer feedback, microcontroller processing, and laser interruption time-of-flight techniques to study the conditions leading to steady-state, maximal draw of polyester blend fibers. The applications of this device are broad: it may be used to study the transient drawing behavior of an extensive variety of monofilaments.
Stress analyses by the finite element and theory of elasticity methods are used to predict the stress fields and intensities in biconvex lenses subject to the contact forces of mounting. In particular, the effects of contact stresses produced by retainer rings are investigated. Typical retainer ring geometries are utilized in the study. Stress distribution data are related to the stress birefringent characteristics of glass, and the effects of mounting forces on the performance of optical elements are predicted. Optical retardation due to stress birefringence as a function of lens radius is presented in graphical form. Results of the numerical analyses are verified by the photoelastic method. Effects on lenses using typical mounting methods are investigated and compared to the analytic predictions. Experimental results correlate well with the analytical predictions. Results of this research indicate that properly designed and constructed retainer ring mounts produce localized stress birefringence effects which occur only in the area of contact.
Flat blade flexure stages have attracted attention for many years because of their potential for producing smooth, large-stroke and hysteresis-free motions, especially close approximations of rectilinear motion. Although smooth operation has been demonstrated many times over, close approximations of rectilinear motion have been rare and achieved at relatively great cost in time and facilities. This has been true because most investigators have relied on 'composite flexures' in which each flexure element is assembled form as many as five separate pieces, all of which need to be aligned to each other as well as the rest of the instrument in which each flexure is only one element. 'Monolithic flexures' have just recently become commercially available and make possible of the first time the precise assembly and alignment of blade flexure systems with a modest investment in time and resources. This resources investigates the precision behavior of a simple flexure stage constructed with monolithic blade flexures and compares it with the behavior attainable from a similar stage using composite flexures. The natural trajectory of such a flexure stage is described and equations for the deviations from the ideal trajectory, parasitic motions, are developed. The results of the analysis are compared to the actual results from testing a commercially available simple monolithic flexure stage.
Optical determination of the spatial period of monocrystalline silicon is a first step toward such diverse goals as an atom-based replacement for the artifact kilogram, reckoning the masses of certain elementary particles, and measurement of the molar Planck constant. The needed measurements are realized through microfringe interferometric precision with a presently achievable accuracy of the order ot 0.01 ppm. Application of such subnanometer standards to x-ray and particulary gamma-ray wavelength measurement requires accurate interferometric angle measurement nowadays effective at the sub-milli-arcsecond level. From results obtained to date, one can infer certain constraints on the future direction of subpicometer interferometry and sub-milli-arcsecond goniometry.
Traditional x-ray mirrors are quite expensive because of the fabrication cost involved in achieving a very high surface finish of the order of 15 angstrom or better. Currently, zerodur, and silicon carbide are commonly used as the substrate materials of choice for x-ray mirrors, and the required surface finish is achieved thorugh traditional through traditional polishing methods, which are very expensive and time consuming. The cost of instruments for many new applications in the areas of biomedicine, nondestructive testing and space can be greatly reduced by using the replication methods for producing x-ray quality grazing-incidence type mirrors. This paper presents the optical and optomechanical design for a Wolter type I mirror and its mount, and the fabrication methods used to produce a low cost replicated nickel mirror. The finite element analysis (FEA) results for this mirror are also presented. The fabrication steps including the design and nickel and gold plating of the aluminum master mandrel used for the replication are also discussed. A surface finish of 10-15 angstrom was achieved for a mirror with a wall thickness of only 1 mm for such an electroformed mirror. These kind of replicated x-ray mirrors can result in a major saving in the weight as well as cost, while also making the resulting instruments much more compact and rugged.
This paper describes a novel long-scanning reflection ellipsometer to characterize large thin films. The ellipsometer uses a frequency stabilize Zeeman-split He-Ne laser as the source. Two common-path left and right circularly polarized beams, with a slight frequency difference, work as the incident beams. Beat frequency signals are detected from the reflected beams on a sample, and the thin film properties are studied. An optical common-mode rejection technique is employed to minimize the effects of environmental conditions. Measurements are not sensitive to low frequency noise and ignore any electronic dc offset effects. The variaitons of the beam intensities of the source do not affect the experimental results. The optical system is designed to be arranged on a long air-bearing slide with an autofocus system of 0.1 micrometers resolution in the range of 25 mm. Measurements will cover the range from 3 micrometers to 600 mm. Experimental results can be taken in the ordinary experimental conditions.
A laser instrument for straightness and alignment measurements with the sliding reflector is described. The instrument provides straightness testing with accuracy of 2im/m at the smoothing time of 3 s.A new method of suppression of the disturbance caused by air turbulence is suggested.
The coefficient of moisture expansion (CME) of a material needs to be well known to accurately predict moisture induced dimensional changes and account for them is the design of large, stable optical benches. Historical methods for measuring CME are identified and discussed. The uncertainties associated with those earlier methods are due to using two different coupons to measure the length and weight change, or the interruption of the coupon environment to perform the measurements. The state-of-the-art CME apparatus described has eliminated these uncertainties by measuring the weight and length change simultaneously on one coupon. The patented design uses two opposing linear variable differential transformers to precisely measure the coupon length change while suspended from a Cahn precision balance to accurately measure the coupon weight change. The resulting determination of CME is accurate to better than +/- 10 ppm/% moisture. The apparatus is described in detail and the innovative design attributes that enable precise CME measurements to be made are discussed. Typical test data is also presented and discussed.
A measurement system utilizing interferometry and correction method has been developed to conduct fast and accurate measurement of ultrathin film thickness and spacing between two separated surfaces. According to the intensity of the interference pattern and the correction method, the ultrathin thickness or spacing is obtained exactly and quickly. After diffracted by a concave grating, the entire visible spectrum of the interference pattern is received simultaneously with a CCD array. Due to the numerical differentiation and average data processing method, the impacts of the light source, the reflecting surfaces, the grating and the CCD array are eliminated automatically. A numerical filtering technique used in the system significantly reduces the noise, thereby yielding a good signal to noise ratio. An ultrathin thickness of (lambda) /20 ((lambda) is the wavelength) is obtained by a numerical analysis of the measured data, which is remarkably less than the limitation, (lambda) /4, by the conventional method.
Significant reduction in weight of optomechanical systems is possible through the use of three new technologies: metal matrix composite materials, Meinel type telescope structures, and shape optimization of mirror substrates. These technologies are successfully employed in a 400 mm aperture f/1.5 dual channel visible/infrared catadioptric telescope system designed and built at the Optical Science Center, University of Arizona. This system is designed for remote control and is operated in an environment characterized by wide temperature shifts as well as severe mechanical vibration. The telescope is a 400 mm aperture f/5 Ritchey-Chretien, with a 1 degree field of view. A Meinel type telescope structure is employed in combination with a single arch sandwich mirror to reduce telescope weight to about 7 kg. An aluminum reinforced with silicon carbide metal matrix composite is used thorughout the telescope, with a metal matrix composite foam as the shear core of the sandwich primary mirror. The dual channel optical bench employs a high performance focal reducer and is constructed of the same type of metal matrix composite used in the telescope. A passive athermalization scheme provides optical aberration correction over a wide range of temperatures, and is combined with a motorized internal focus to avoid moving the telescope secondary. Design and construction of the telescope was facilitated by a process of interactive optical design, computer aided mechanical layout, and finite element analysis. System performance was successfully simulated prior to final assembly using results from actual optical tests. The final system displayed good performance and represents a successful first use of a number of technologies, including the foam core single arch metal matrix composite primary mirror.
This paper describes a design study of the KAO (Korea Astronomy Observatory) 1m telescope. The telescope uses an F/2.7 zerodur primary mirror which has a double arch back contour shape. For the zenith pointing, the primary mirror is to be held by a 6-point axial support system at the back surface. For Horizon, a 3-lateral support system is to be designed and located at the center of gravity of the mirror. In this paper, a parametric design study of a double arch back contour shape is to be performed to meet an optical surface deflection requirement, a surface RMS wavefront error of (lambda) divided by 10, using the finite element program, ANSYS, for the mechanical surface deformation, and the PCFRINGE program for the evaluation of the optical performance. Additionally, the static and modal frequency analysis of the truss structure and yoke were performed.
An optical fiber pH sensor based on the surface absorption of methylene blue dye is reported. Previously obtained results for this sensor have indicated a large linear operating range (3-10 pH) coupled with a relatively short response time and immunity to ionic concentration. Further investigations are reported which include testing reproducibility, accuracy, and sensitivity. In addition to this, a two wavelength referencing technique is introduced where the sensor is illuminated by two wavelengths in sequence in a time domain multiplexed manner. The performance of the sensor in terms of temperature stability and immunity to small perturbations to the launch conditions is improved by the application of the multiplexing technique. Particular attention is given to the ability of this sensor to measure pH at very low ionic strength and the geometry of the sensing element has been refined to reduce the response time to below 45 seconds for solutions of ionic strengths of 100 microsecond(s) . These measurements are significant since many applications for pH measurement require operation at such low ionic concentrations, e.g. underground water monitoring. Results are also included for higher ionic concentrations such as those encountered in blood pH measurement and other medical applications.
A new line of very high precision actuators has been developed by the author (Hatheway, 1988). One of the features of these actuators is a very high degree of linearity over the full range of motion. The actuators are based upon an elastic transducer design which should make both the linear and nonlinear characteristics of the actuator predictable from the basic theory of elasticity. The author has measured the characteristics of a typical actuator based upon these elastic principles. In this report he shows that the nonlinearities are predictable from the elastic theory for large displacements. The actuators may be calibrated for 'open-loop' operation in applications requiring accuracies to 1.8 parts in 10,000 which is the limit of accuracy of this study.
The far UV spectroscopic explorer grating mechanical design and analysis are discussed. These gratings are large (266 mm X 275 mm), and unique design constraints were imposed to maintain optical performance. FEM results of deflection and stress are presented. Requirements driving the unconventional grating design and its mount are addressed, including the plan to accommodate remote vacuum alignment in multiple degrees of freedom.
In this paper, some design criteria and key points on ultrahigh resolusion positioning corn ponents were discussed, and the material selection for different functional elements were studied in detail. Several typical and special design were advanced with figues illustration.
Dimensional size was important for a commercialized diode-pumped lasers with green light output. This paper advanced laser structure design for transverse size limited or longitudinal size limited, furthermore, the general rule for optimum structure design were given.
A novel integrated silicon micro-mechanical/optical pressure sensor is presented. Using the standard IC process and the silicon anisotropic etching technology, an optical strip waveguide which functions as the pressure-sensing and optical signal transmitting element, a thin silicon membrane layer and a photoelectric detector are all integrated on a three-dimensional silicon wafer. The sensor's structure, principle of operation, fabrication processes and test results are presented. This novel silicon integrated micro-mechanical/optical pressure sensor which is small, reliable, sensitive, inexpensive and does not need an external electrical supply may have many potential applications.
Keywords: pressure sensor, micro-mechanical, thin silicon membrane, optical strip waveguide, anisotropic etching
OCA Applied Optics has developed and demonstrated a rapid, automated technique for the fuguring of precision aspheric surfaces on fused silica optical elements using plasma assisted chemical etching (PACE) methodology. In this paper we discuss the pre-processing methods and suitable PACE removal depth strategies for fused silica necessary to ensure that final PACE-finished surfaces meet current low-scatter optical standards. We also describe models for aspheric surface figuring using the patented PACE process which account for substrate dielectric losses and other effects and allow us to define the parameters needed to efficiently correct surface figure errors. FInally, we demonstrate the capabilities of the final PACE figuring method on a fused silica test substrate.
OCA Applied Optics has developed and demonstrated a rapid, automated technique for the surface figuring of precision aspheric silicon and silicon-clad optical elements using a patented plasma assisted chemical etching (PACE) methodology. In this paper we discuss the preprocessing methods and suitable PACE removal depth strategies to ensure that final PACE- finished silicon surfaces meet current low-scatter optical standards. An aspheric surface figuring model for the PACE process is also described.
Electrochemically grown nickel-based alloys (electroless nickel) are currently used as a polishable coating on lightweight metal and nonmetal substrates for high performance applications ranging from large spaceborne telescopes to cryogenically cooled optical instruments. The performance of nickel plated optics is currently limited by bi-metallic dimensional stability issues. OCA has determined that careful selection of processing parameters and plating bath chemistries leads to a family of coatings whose thermal expansion curves can be tailored to better match those of ultra-lightweight substrate materials of interest over useful temperature ranges. This paper presents a discussion on the nature of the thermal expansion mismatch and a description of the fundamental methodology used in developing stable EN-substrate couples.
We describe the design and analysis of a prototype Beryllium telescope with a near one meter aperture for space laser altimeter application. The design target for this telescope is 25 kG mass, 100 micro-radian boresight, and 100 micro-radian blur spot. We first conduct a parametric study to optimize the design of the primary mirror. Our study shows that the degree of lightweighting is limited by the quilting parameter which is fixed by optical fabrication standards. We further discuss the options for the metering structure design, and the rationale for our selection. A number of analysis were conducted to validate the final design. To assess the optical performance, we model the telescope using an in-house program, SPOT, which enables individual allocation of various 'real-life' optical aberrations. The result of our modeling indicates an expected spot size of 53 micro-radians. We model the primary mirror and the telescope using finite element technique; our analysis indicates that the telescope has adequate margins to survive the launch environment and meet boresight requirements during operations. Lastly, we discuss some of the lessons learned through our experience, and suggest some possible future design approaches.
OCA Applied Optics is fabricating an innovative 0.9-meter diameter, ultra-lightweight, all- beryllium space telescope for the NASA Goddard Space Flight Center Multi-Beam Laser Altimeter. The telescope is also a prototype for the GSFC Geoscience Laser Altimeter System for measuring ice sheet topography, temporal changes in topography, cloud heights, planetary boundary heights, aerosol vertical structure, and other topographical features. The telescope is being manufactured using efficient and innovative approaches to optical grinding and polishing and electroless nickel plating of the large parabolic primary mirror. Advancement in producibility were accomplished utilizing novel tooling concepts and advances in manufacturing equipment. Improvements include rapid material removal in grinding and polishing and uniformity of electroless nickel plating.
OCA Applied Optics has devised and optimized methods for designing, building and testing precision mirror systems whose performance is not compromised by large changes in environmental temperature. A key to our approach is the use of a single material for the construction of all telesope components to minimize the differences in the contraction and expansion of the components with changes in the operating temperature. Specifically, we designed and built a simple, on-axis, monometallic telescope suitable for cryogenic testing in order to investigate and optimize methods for accurately testing the optical performance at cryogenic temperatures. We then designed and built a sophisticated, off-axis monometallic telescope representative of the current technology in advanced spectrometer instruments for deep-space applications. The novel design of this telescope facilitated assembly, alignment, and testing. We characterized the performance of the instrument in both laboratory and cryogenic environmental conditions. The results of these tests show that the instrument focus position and image quality showed negligible change at cryogenic temperatures, compared to a room temperature environment. This research has already contributed to improved performance and reduced cost for advanced reflective optical instruments for several space applications.
Optomechanical bonding or mounting with adhesives has demanding requirements which are more severe than most other bonding applications. Stress must be minimized to prevent optical distortion and must be considered over the entire operating temperature. No failures are desired along the bondline and bonded components must remain precisely located over their entire lifetime. UV Curing adhesives can offer advantages for fastening or mounting of optics if the mechanical design is configured to take advantage of the handling characteristics of the adhesive. Use of these materials simplifies any process that requires critical alignment or exact positioning. This paper describes some of the considerations which must be taken in order to choose the best UV adhesive and how to control them for maximum performance in a system.
A single-mode-fiber-compatible SC-type optical module (SC module) is developed. This module realizes low optical coupling loss and low cost by means of plastic molding technology and the developemnt of automatic fabrication equipment. The SC module consist of a plastic adapter to be compatible with a SC-mode-fiber connector and a plastic housing for optical components: a GRIN rod lens and an optical transmitting/receiving device. The housing is made from a plastic with an extremely low thermal expansion coefficient, and is designed as acylindrical structure for thermal stability. It has a mount for an optical device, a lens holder, and a fiber connection. A zirconia ceramic sleeve, installed in the housing by insert molding technology, is employed to obtain a high plug coupling strength and the optimum optical power coupling. The optical axis between the zirconia sleeve and GRIN rod lens is adjusted automatically and accurately by insert molding technology: the lens holder is formed by the same plastic mold that holds the zirconia sleeve along it. In order to lower the cost, the optical module is fabricated using automatic fabrication equipment, which carried out the processes from supplying the optical device to fixing it with UV-cured resin. The following characteristics of the SC module are obtained from experimental results where total optical loss was 6dB. The portion of 5.5dB of the total loss is contributed by the GRIN rod lens. The remainder is the excess loss of 0.5dB due to assembly. The thermal stability is found to be within 0.1dB in the temperature range from -10 degrees to 65 degrees C.
The Imager for Mars Pathfinder is a stereo multispectral CCD camera designed to support a variety of science experiments from the Martian surface. The camera combines a straightforward imaging system based on a pair of Cooke triplets, fold optics, and a divided 512 by 256 pixel CCD with a complement of spectral and solar filters on two filter wheels. Aluminum and titanium component mountings on an aluminum optical bench provide for a complete pointing and imaging system having a mass of less than 3 kg. The az-el gimbal utilizes gearhead stepper motors to provide a field of regard of 370 degrees in azimuth and 156 degrees in elevation, in support of stereo and monoscopic panoramas and atmospheric studies. This paper discusses mechanical aspects of the optical component mountings and adjustments, as well as structural and mechanical aspects of the gimbal.
In order to enhance the measuring accuracy of angular displacement, it is important to form high accuracy and superior quality of moire fringe signals. They are strongly affected by the radial disturbance of grating disk which is mounted on the shaft of bearing system. Specifications for the hydrodynamic bearing system often call for much higher radial accuracy and stability. This requirement poses unique challenges for the design of the bearing system. In this paper, the design of precision three-lobe hydrodynamic bearings is described, and lubricant performance of some structure parameters is analyzed. The radial accuracy of this bearing system is within 0.023 micrometers .