This PDF file contains the front matter associated with SPIE Proceedings Volume 6671, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

Mirror technology is a critical enabling capability for the James Webb Space Telescope (JWST). JWST requires a Primary Mirror Segment Assembly (PMSA) that can survive launch, deploy and align itself to form a 25 square meter collecting area 6.5 meter diameter primary mirror with a 131 nm rms wavefront error at temperatures < 50K and provide stable optical performance. At the inception of JWST in 1996, such a capability did not exist. A highly successful technology development program was initiated including the Sub-scale Beryllium Mirror Demonstrator (SBMD) and Advanced Mirror System Demonstrator (AMSD) projects. These projects along with flight program activities have matured and demonstrated mirror technology for JWST. Directly traceable prototypes or flight hardware has been built, tested and operated in a relevant environment. This paper summarizes that technology development effort.

The Kepler primary mirror assembly (PMA), designed and fabricated by the Brashear Division of L-3 Communications (Brashear), consists of a 1.45 meter, lightweight, frit bonded, ULE mirror supported on a composite strut hexapod. During the early stages of fabrication, finite element analysis results are integrally combined with the in-process mirror metrology to determine the cryogenic, gravity free surface figure of the Kepler primary mirror. The successful operational design of the primary mirror assembly hinges upon the accurate estimation of the cryogenic figure. This paper describes a combined test and analysis approach developed by Brashear which yielded an analytical FEA cryogenic surface distortion within 8% of the actual measured rms surface. The primary mirror thermally induced surface distortion is strongly influenced by the nonlinear, strain rate dependent adhesive mechanical properties. Because of the difficulty in accurately characterizing and implementing the adhesive behavior, an optical test of a representative geometry is used to characterize the distortion caused by the adhesive and bond pad. By correlating FEA results to the optical results, an equivalent, linear elastic, adhesive stiffness is derived and used in the primary mirror assembly cryogenic FEA analysis. Additionally, during in-process metrology, the gravity induced FEA surface figure for each test configuration is numerically subtracted from the raw metrology data in order to estimate the gravity free figure. Thus, the accuracy of the final in-process mirror figure is dependent upon the accuracy of the FEA results which are subtracted. The in-process results are then compared to the final gravity free figure for the integrated primary mirror assembly which is obtained by averaging the metrology results for two diametrically opposed support orientations.

Deterministic subaperture finishing technologies, such as Magnetorheological Finishing (MRF^(R)) are becoming the industry standard for finishing high precision optics with complex shapes, such as aspheres. However, astronomical or very large optics were beyond the scale of existing capabilities and relied on traditional, artisan-based methods of manufacture. It is not uncommon for these critical parts to spend a year or more in production. Recent developments from QED Technologies(R) have expanded MRF technology to enable the manufacture of meter-scale aspheric optics. QED, in conjunction with the Steward Observatory Mirror Laboratory (SOML) at the University of Arizona, demonstrated the fabrication of an 840 mm diameter convex asphere with 1.3 mm of aspheric departure from a best-fit sphere. Long-trace profilometry scans were initially performed at SOML to characterize the surface. A first figure correction polishing iteration was conducted at QED Technologies in Rochester, NY on a meter-class MRF machine (Q22-950F). The correction improved the surface to within the capture range of a full aperture interferometric test performed at the Mirror Lab. A final polishing iteration at QED improved the surface to meet the optic specifications.

Flat mirrors of around 1 meter are efficiently manufactured with large plano polishers and measured with Fizeau interferometry. We have developed technologies and hardware that allow fabrication and testing of flat mirrors that are much larger. The grinding and polishing of the large surfaces uses conventional laps driven under computer control for accurate and systematic control of the surface figure. The measurements are provided by a combination of a scanning pentaprism test, capable of measuring power and low order irregularity over diameters up to 8 meters, and subaperture Fizeau interferometry. We have developed a vibration insensitive Fizeau interferometer with 1 meter aperture and software to optimally combine the data from the subaperture tests. These methods were proven on a 1.6 m flat mirror that was finished to 6 nm rms irregularity and 11 nm rms power.

Ball Aerospace has constructed a new collimator for interferometric and image quality testing of meter scale optical systems under cryogenic, vacuum conditions. Termed the Vertical Collimator Assembly (VCA), it features 1.5 m diameter off-axis parabolic and calibration flat mirrors. In order to preserve as large a volume as possible for the unit under test, the main platform is suspended inside its vacuum chamber by a hexapod, with the parabolic mirror mounted overhead. A simultaneous interferometer facilitates collimator alignment and monitoring, as well as wavefront quality measurements for the test unit. Diffusely illuminated targets may be employed for through-focus image quality measurements with pinholes and bar targets. Mechanical alignment errors induced by thermal and structural perturbations are monitored with a three-beam distance measuring interferometer to enable mid-test compensation. Sources for both interferometer systems are maintained at atmospheric pressure while still directly mounted to the main platform, reducing vibration and stability problems associated with thermal vacuum testing. Because path lengths inside the ambient pressure vessels are extremely short, problems related to air turbulence and layering are also mitigated. In-chamber support equipment is insulated and temperature controlled, allowing testing while the chamber shrouds and test unit are brought to cryogenic temperatures.

The HMD (Helmet Mounted Display) visor is a sophisticated article. It is both the optical combiner for the display and personal protective equipment for the pilot. The visor must have dimensional and optical tolerances commensurate with precision optics; and mechanical properties sufficient for a ballistic shield. Optimized processes and tooling are necessary in order to manufacture a functional visor. This paper describes the manufacturing development of the visor for the Joint Strike Fighter (JSF) HMD. The analytical and experimental basis for the tool and manufacturing process development are described; as well as the metrological and testing methods to verify the visor design and function. The requirements for the F-35 JSF visor are a generation beyond those for the HMD visor which currently flies on the F-15, F-16 and F/A-18. The need for greater precision is manifest in the requirements for the tooling and molding process for the visor. The visor is injection-molded optical polycarbonate, selected for its combination of optical, mechanical and environmental properties. Proper design and manufacture of the tool - the mold - is essential. Design of the manufacturing tooling is an iterative process between visor design, mold design, mechanical modeling and polymer-flow modeling. Iterative design and manufacture enable the mold designer to define a polymer shrinkage factor more precise than derived from modeling or recommended by the resin supplier.

Telescopes are ultimately limited by atmospheric turbulence, which is commonly characterized by a structure function. The telescope optics will not further degrade the performance if their errors are small compared to the atmospheric effects. Any further improvement to the mirrors is not economical since there is no increased benefit to performance. Typically the telescope specification is written in terms of an image size or encircled energy and is derived from the best seeing that is expected at the site. Ideally, the fabrication and support errors should never exceed atmospheric turbulence at any spatial scale, so it is instructive to look at how these errors affect the structure function of the telescope. The fabrication and support errors are most naturally described by Zernike polynomials or by bending modes for the active mirrors. This paper illustrates an efficient technique for relating this modal analysis to wavefront structure functions. Data is provided for efficient calculation of structure function given coefficients for Zernike annular polynomials. An example of this procedure for the Giant Magellan Telescope primary mirror is described.

A novel technique based on the use of a three Gaussian beam interferometer to obtain roughness information about smooth optical surfaces is described. The technique is based on the heterodinization of three coherent optical beams. One of the beams is used as a probe beam after being focused and reflected from the surface under test. A second beam is generated to be reflected by a reference surface. The last beam is obtained from the first diffraction order of a Bragg cell and thus, it is shifted in its temporal frequency. The three beams are coherently added at the sensitive plane of a photodetector that integrates the overall intensity of the beams. It will be demonstrated analytically that the electrical signal at the output of the photodetector is a time varying signal whose amplitude is proportional to the surface's local vertical height. The frequency response of the proposed system is characterized experimentally by measuring the profile of three different blazed-gratings. Once the system is calibrated, we present measurements of the roughness of an optical flat.

We have measured and modeled the thermal shock fracture of the commercially available BK-7 borosilicate crown optical glass as a function of surface finish prior to thermal shock testing. For surfaces lapped with alumina abrasives in the range 5 μm to 40 μm, the critical temperature drop for fracture in thin disk samples increases with diminishing abrasive size, and changes from 123.7±1.1 °C (for surfaces lapped with 40 μm abrasives) to 140.2±2.8 °C (for surfaces lapped with 5 μm abrasives.) We correlate the measured thermal shock (critical) temperature drop with the glass thermal and mechanical properties, including the fracture toughness, and the depth of surface cracks induced by the lapping process. We distinguish between "severe" and "mild" thermal shock conditions in terms of the applicable heat transfer coefficient and Biot number. We estimate that the depth of the strength controlling cracks on the edge of the disk samples was about 55-70 μm.

Fabrication of fused silica optics for high-powered Nd:YAG laser applications commonly employs grinding and polishing processes to generate smooth, specular surfaces. The industry often describes such surfaces as "laser quality" after assessment against such gauges as surface roughness or scratch-dig standards; however, surfaces deemed acceptable have performed variably when actually exposed to high-powered laser illumination. Traditional processes to prepare such surfaces have often relied on rules of thumb, but we have found a convenient and simple method to help the fabricator optimize expressly for a desired performance metric, that of low subsurface damage. Subsurface damage often has immediate impact on susceptibility to destruction by high-power laser illumination, and we find that this damage is not universally related to surface roughness. In addition, we show that surface roughness measurements may vary depending on the measurement method used, such as white light interferometry (WLI), variable angle spectroscopic ellipsometry (VASE) or atomic force microscopy (AFM).

We report on use of the magnetorheological finishing (MRF) spotting technique to estimate subsurface damage (SSD) depth resulting from deterministic microgrinding for polycrystalline alumina (PCA). With various microscopy techniques, we show how surface roughness evolves with the amount of material removed by an MRF spot. Two stages are identified. In the first stage the induced damaged layer and associated SSD from microgrinding are removed, reaching an optimal value of surface roughness. Here, the initial peak-to-valley (p-v) surface roughness from grinding gives a measure of the SSD depth found by spotting. In the second stage, where more material is removed from the nonrotating surface, the resulting surface roughness begins to show the interaction between MRF abrasive particles and the material's microstructure (crystal grains), i.e., the "MRF signature" for a specific material. We can examine the "MRF signature" across grains using power spectral density and characterize surface features that contribute to surface roughness.

In this presentation an impression is given of technical developments within Philips High Tech Plastics, a European supplier with a production facility in Suzhou, China. Philips HTP is making precision plastic and optical parts for the mass consumer electronics market; the largest part of its current business is camera objective lenses and actuators for mobile phone. A supplier in consumer electronics has to deal with Moore's law, being one of the most specific characteristics of this particular market. This law says that every 18 - 24 months the performance of computers will double, while the price at the same performance will be halved, at the same rate. So this law also applies to lenses that are mounted on a silicon chip; the product life cycle is short, typical 2-3 years, and the next generation needs to have an ever-higher performance. The pixels are getting smaller and smaller, so the resolution of the lenses has to follow. This means a continuous tightening of the tolerances in mold making, molding and assembly, and the improvements are needed at a high rate. In the presentation is described what challenges in ever increasing precision are encountered, developments that are carried out to meet those, and in what extent Philips HTP is successful reaching the required goals.

The use of aspheres gives optical designers extended possibilities to develop lenses with higher speed, lower distortion and better performance in ever smaller dimensions which would be nearly impossible to realize in a mere spherical design. For the aspherical elements careful considerations on tolerancing, measurability and manufacturability are crucial both for the as-built performance and for ensuring stable and cost-effective machining. Close collaboration between optical design and the optical shop in charge is needed to ensure the best possible solution at minimum cost. High precision aspheres for professional cine lenses with deviations from their best-fit-sphere in the range of millimeters are presented. For them, figure errors down to 0.1 microns and slope errors down to 0.1' were achieved.

A method of surface figure measurement is described based on the transmitted wavefront of an optical element obtained from a Mach-Zehnder interferometer. Given known values for the refractive index and center thickness, along with the samples transmitted wavefront, the unknown surface profile is reconstructed in a deterministic way. The technique relies on knowledge of one of the surfaces of the element, such as an easy to measure plano or spherical surface, and is well-suited for testing aspheric surfaces. Reverse raytracing is used to remove the effects of transmission through a thick lens and to remove induced aberration associated with the interferometer. In the interferometer, the wavefront transmitted through the sample is tested against a plano reference. In order to reduce the high frequency fringe content of the interferogram, the sample can be tested in an immersion solution. This method also has the ability to make measurements on multiplexed surfaces, such as a lenslet array, which traditionally can not be measured without moving the sample. The surface profile of a plano-convex lens has been produced and verified against other metrology techniques for calibration purposes. Surface measurements on a lenslet array are also presented.

Wavelength scanning interferometry offers many advantages over traditional phase shifting interferometry, most significantly the elimination of mechanical movement of the part/s for phase modulation by implementing a tunable light source. Further, Fourier analysis on the interference time history enables this technique to accurately measure distances, treating the distance between two optical surfaces as an interferometric cavity. We propose to use a newly acquired wavelength scanning Fizeau interferometer from Zygo Corporation, the MST (Multiple Surface Transform) to explore the limits of absolute thickness metrology to measure an opaque cavity, such as a gauge block. While transparent cavities can be measured with ease in a Fizeau setup, opaque cavities need additional optics. A two mirror Sagnac configuration in conjunction with the interferometer from Zygo Corporation is used to measure the length (thickness) of a 1 inch gauge block. Current gauge block measurements rely on comparison methods to determine the fractional length with respect to a reference or master gauge block or use techniques which require the absolute length of the gauge block to be previously known. By using wavelength scanning interferometry, the absolute length of the gauge block can be determined directly within limits of the repeatability of the instrument. While other techniques implement a point by point approach for measurement or use interpolation methods, we simply use a large aperture to provide the thickness variation over the sample. Experimental results of a 1 inch gauge block along with an uncertainty estimate are discussed.

The need for segmented wave front measurements has been rocketing for several years. The applications are various: thickness of metallic masks, diffracting elements, phasing of the primary segmented mirrors of telescopes, such as the Keck telescope, laser beam coherent recombination... Lateral shearing interferometers are common wave front sensors, used with success to test classical optical components. This technique does not require a reference wave, which is a major advantage. The lateral shearing interferometry has also proved successful to analyze segmented wave front; results of such a measurement by a diffraction-grating based interferometer are presented and analyzed. We dwell upon quadri-wave lateral shearing interferometers (QWLSI), which offer the possibility to characterize two-dimensionally the wave front, in a single measurement. This technique combines accuracy and qualities such as compactness and simplicity. Moreover, a chromatic regime of lateral shearing interferometers based on diffraction grating can be pointed out; this allows a two-color analysis to greatly extend the dynamic range. In the first parts we will present general considerations on QWLSI and segmented surface; then a technique to increase the dynamic range is investigated both theoretically and experimentally.

Interferometers with additional test optics are frequently used for measuring aspherical optical surfaces. In optical testing it is desirable to separate the figure measurement errors due to the test surface from figure errors that arise in the test equipment. For axially symmetric optics this is accomplished by rotating the surface being measured with respect to the test system. The data can then be processed to separate the non-axially symmetric errors that are fixed in the test system and those that rotate with the part. The axially symmetric errors cannot be distinguished with this technique. In this paper we present a variation of this technique for off-axis aspheric optics. The rotation is performed by rotating the test surface about the optical axis of its parent asphere, which may be outside the physical boundary of the test surface. As these rotations cannot be large, this motion is better described as a shear of the optical surface with respect to the test optics. By taking multiple measurements with different amounts of rotational shear and using maximum likelihood estimation methods, one can separate the errors in the test optics from the irregularity in the optical surface.

Phase shifting interferometry (PSI) is a highly accurate method for measuring the nanometer-scale relative surface height of a semi-reflective test surface. PSI is effectively used in conjunction with Fizeau interferometers for optical testing, hard disk inspection, and semiconductor wafer flatness. However, commonly-used PSI algorithms are unable to produce an accurate phase measurement if more than one reflective surface is present in the Fizeau interferometer test cavity. Examples of test parts that fall into this category include lithography mask blanks and their protective pellicles, and plane parallel optical beam splitters. The plane parallel surfaces of these parts generate multiple interferograms that are superimposed in the recording plane of the Fizeau interferometer. When using wavelength shifting in PSI the phase shifting speed of each interferogram is proportional to the optical path difference (OPD) between the two reflective surfaces. The proposed method is able to differentiate each underlying interferogram from each other in an optimal manner. In this paper, we present a method for simultaneously measuring the multiple test surfaces of all underlying interferograms from these superimposed interferograms through the use of a weighted least-square fitting technique. The theoretical analysis of weighted least-square technique and the measurement results will be described in this paper.

Optical designers are becoming increasingly aware of the importance of specifying and tolerancing slope errors on optical surfaces, especially aspheric surfaces. Slope errors can degrade system optical performance - in some cases even if the peak to valley surface figure errors meets the optical design tolerance analysis. With this awareness, more optical engineers are putting requirements for peak surface slope on optical element drawings. This puts pressure on optical fabricators to understand slope specifications and react to these requirements, and use the appropriate metrology instrumentation to ensure final system performance. This paper will discuss appropriate ways to specify slope errors, and the challenges and limitations of measuring slope errors with commercial interferometers. The optical designer should be aware of how slope errors are measured on Fizeau interferometers and should specify the spatial intervals of interest when tolerancing aspheric elements. Peak slope error measurement is prone to erroneous measurement errors due to surface contamination, environmental errors, and pupil focus. Finally, filtering has a strong influence on surface slope calculations. Practical examples of slope specifications and experimental results will be presented.

Techniques of Speckle Metrology are used for the study of the onset of chatter during machining process. In this method, it is found that with an increase of cutting depth, the cutting regime was changed from chatter- free cutting to one with chatter. This is detected by the offline surface texture analysis of the work-piece using speckle effect. Laser speckle is an interference pattern produced by light reflected or scattered from different parts of the illuminated surface. It is the superposition of many wavefronts with random phases, scattered from different parts of the rough surface. Hence, the information of surface texture is encoded in the speckle pattern even though it is a random phenomenon. The statistical study of speckle contrast and speckle size distribution can be used to extract the information about the roughness of the surface from which the light is getting diffusively reflected. Given that machining processes are very complex due to their non-linear and non-stationary characteristics, and since many process- variables cannot be directly measured, process- monitoring is a challenging problem. Chatter is one of such problems, which is essentially the self-excited vibration during machining that will adversely affect the surface finish, tool life and thereby affecting the quality of the machined surface. In the present study a tapered work piece is machined to form a cylindrical piece, by continuously varying the depth of cut. As the depth of cut increases the surface finish is expected to deteriorate, mainly due to the onset of chatter vibrations. To analyze the surface texture characteristics, the speckle pattern obtained by illuminating this curved surface using a collimated laser beam (5mW Diode Laser at 676nm wavelength.). The laser beam was made to incident obliquely to the curved surface of the work piece, and the speckle pattern was recorded using a Charge Couple Device (CCD) camera. The beam was scanned along the axis of the work-piece and recorded the speckle pattern at different regions at constant intervals The speckle contrasts of the patterns are evaluated as the ratio of the normalized standard deviation to the normalized RMS height of the histogram. It is found that the speckle contrast is decreasing as moving from lower depth of cut region to higher depth of cut region. An abrupt decrease of the speckle contrast is observed at the beginning of the onset of chatter vibrations. This method can be extended to online detection of chatter, which is not possible with the conventional methods, like stylus methods. This can also be used for online Tool Condition Monitoring (TCM).

Standard interferometric testing of aspheric surfaces makes use of a null optic that is matched exactly to the surface under test. This leads to part specific null lenses having to be designed, manufactured and tested for every aspheric surface to be tested. This paper discusses design issues associated with testing a range of fast aspheric optical surfaces with a single partial- or pseudo-null lens. Collecting the light that is reflected from a range of fast aspheric surfaces becomes one of the major design concerns. The partial null should also provide a reduction in the wavefront slope. The slope of the wavefront, or more specifically the fringe frequency created by the interference of the test and reference wavefronts, must not exceed the maximum measurable fringe frequency of the detector used in the system. Furthermore, since the null condition has been removed from the interferometer, light no longer travels the same path to and from the test surface. This situation leads to retrace errors introduced into the test wavefront by the interferometer. These errors must be calibrated as part of the measurement process in order to recover the aspheric test surface. The ability of the system to be calibrated must be considered in the design of the partial null.

In the manufacturing process of aspheric glass lenses the grinding step plays a key role both in respect of the final quality of the polished lens as well as in respect of manufacturing costs. Therefore, the form of the grinded surface must be measured with high precision. The typically used tactile measuring machines provide sufficient precision regarding depth resolution but suffer from limited lateral resolution. In particular it is not possible to detect surface and sub-surface damages which essentially influence the duration of the subsequent polishing process. In order to detect these damages we set up and tested a scanning short-coherence interferometer very similar to optical coherence tomography. The aspheric lens under test is mounted on a rotation stage which can be translated in the lateral direction. The sensor beam of the interferometer is focused onto the sample and can be moved along the axial direction. The precision of the depth measurement is 0.25μm, the lateral positioning precision is 2μm. The system is used to optimize the grinding process for aspheric lenses to minimze sub-surface damages and therefore to maximize processing speed.

Magnetorheological finishing (MRF) is a commonly used computer-controlled polishing (CCP) technique for high precision optical surfaces. The process is based on a magnetorheological abrasive fluid, which stiffens in a magnetic field and may be employed as a sub-aperture polishing tool. Dependent upon the surface error-profile of the workpiece and the polishing tool characteristic (influence function) an individual polishing procedure is calculated prior to processing. However, determination of the influence function remains a time consuming and laborious task. A user friendly and easy to use software tool has been developed, which enables rapid computation of MRF influence functions dependent on the MRF specific parameters, such as, magnetic field strength or fluid viscosity. The software supersedes the current cumbersome and time consuming determination procedure and thus results in considerably improved and more economical manufacture. In comparison with the conventional time period of typically 20 minutes to ascertain an influence function, it may now be calculated in a few seconds. An average quality improvement of 57% relating to the peak-valley (PV) value, and approximately 66% relating to the root-mean-square (RMS) of the surface error-profiles was observed during employment of the artificial computed influence functions for polishing.

In this work we discuss the role that nanodiamond abrasives play in magnetorheological finishing. We hypothesize that, as the nanodiamond MR fluid is introduced to the magnetic field, the micron sized spherical carbonyl iron (CI) particles are pulled down towards the rotating wheel, leaving a thin layer of nanodiamonds at the surface of the stiffened MR fluid ribbon. Our experimental results shown here support this hypothesis. We also show that surface roughness values inside MRF spots show a strong correlation with the near surface mechanical properties of the glass substrates and with drag force.

We developed a new magnetorheological (MR) fluid for studying the relative contributions of mechanics and chemistry in polishing hard materials. The base carrier fluid is a mixture of two non-aqueous liquids. At conventional carbonyl iron (CI) magnetic particle concentrations, removal rates with this formulation were unacceptably low for the polycrystalline optical ceramic aluminum oxynitride (ALON). We overcame this problem by creating a high magnetic solids concentration suspension consisting of a blend of large and small CI particles. Our test bed for experiments was a magnetorheological finishing (MRF) spot-taking machine (STM) that can only polish spots into a non-rotating part. We demonstrated that, using this new MR fluid formulation, we could substantially increase peak removal rates on ALON with small additions of nonmagnetic, nanodiamond abrasives. Material removal with this fluid was assumed to be predominately driven by mechanics. With the addition of small amounts of DI water to the base fluid containing nanodiamonds, the peak removal rate showed an additional increase, presumably due to the altered fluid rheology and possibly chemical interactions. It is possible, however, that this result is due to increased fluid viscosity as well. Interestingly, the microtexture on the surfaces of the ALON grains (albeit-two different ALON parts) showed distinctly different features when spotted with nanodiamonds or with nanodiamonds and water, and an understanding of this phenomenon is the goal of future work. In this paper we describe the difficult fluid viscosity issues that were addressed in creating a viable, high removal rate, non-aqueous MR fluid template that could be pumped in the STM for several days of experiments.

There are four fundamental steps to precision glass aspheric manufacturing: 1) grinding - to generate the rough shape, 2) pre-polishing - to remove subsurface damage and smooth grinding residuals, 3) metrology - to quantify surface figure errors and 4) finishing - to reach final figure and roughness specification. The aspheric pre-polish step is currently the least deterministic process, as conventional sub-aperture tools (e.g. pitch, polyurethane pad) inherently have removal rate variation due to tool misfit, pad wear, or slurry variation over time. This limits the final figure accuracy achievable or at a minimum, leads to significant unpredictability in cycle time. Magnetorheological Finishing (MRF^(R)) offers a very deterministic finishing process, but is limited in its ability to smooth certain spatial frequencies. In this paper, we present a complete polishing process (pre-polishing + finishing) that utilizes a novel combination of MRF and conventional small-tool pitch polishing. This combined approach leverages the strengths of both processes, providing a fast, deterministic, scalable aspheric finishing process to compliment existing grinding technology. Results for a 300 mm rectangular aperture, off-axis section will be presented showing final peak-to-valley quality of better than twentieth wave.

The two major process steps, grinding and polishing, of the classical process chain have to fulfill the following requirements: Grinding: low subsurface damage, no cutter marks and best shape accuracy Polishing: fast removal of subsurface damage by form preserving The goal for the polishing step is a flexible process capable of removing mm³/min by keeping the shape generated by the grinding process or improving the shape in parallel to the required specifications. To be fast a new polishing kinematics is applied. The improvement of the removal rate is in the order of 2-3 compared to a standard asphere polishing processes. The drawback is a huge spatial variation of the removal rate. By application of proper simulation procedures this shortcomings can be overcome, requiring a detailed understanding of the local removal rate. Furthermore an extensive set of analysis tools such as PSD based evaluation of 1 and 2D shape measurements and separation tools for grouping of surface errors are applied. They help to understand and optimize the local polishing action and to define the cut-off wavelength for the final correction step. Results of the simulation, evaluation and experimental results for 3 different kinds of aspheres will be presented to demonstrate the power of described approach.

The Ion Beam Figuring is a well known technique able to correct shape errors on optical surfaces with high accuracy. The size of the ion beam dictates strongly the higher spatial frequencies that can be corrected on the optical surface. The correction of small optics of some cm in diameter or containing high spatial frequencies can be very time consuming or impossible. A system that permits the Ion Beam Figuring of small optical components has been developed in the Astronomical Observatory of Brera (INAF-OAB). It has a small ion beam size and large removal rate. The system employs a concentrator able to force the broader beam emitted from an ion source into a smaller spot having large removal rate. The concentrator is placed between the ion source and the optical surface to be figured and doesn't influence the long term stability of the source. It consists of a conical cavity in which is injected the beam extracted from the grids of the source. The grazing incidence angle of impact of the ions with the walls of the cone ensure a very low level of sputtering of the cone material and meanwhile permits the creation of a very small spot removal function having large removal rate. To demonstrate its functionality a number of test optics has been figured using this system with very good results.

Digital speckle pattern interferometry (DSPI) and digital shearography (DS) are two independent whole-field non-contacting optical methods for nondestructive flaw detection and precision measurements. A multi-aperture arrangement in front the imaging lens provides the grid structure within the speckles to yield desired diffraction halos at the Fourier transform plane. A three aperture arrangement in front of the imaging system is proposed here to combine coherently three waves at the CCD plane and also to introduce spatial carrier fringes within the speckle. One of the apertures is used for imaging the object onto the CCD plane, the second aperture for introducing smooth reference wave, while the third aperture carries a small angle wedge plate to provide the shear. This method allows simultaneous phase evaluation of the out-of-plane displacement and its first order derivative (slope) by filtering the appropriate diffraction halos of the Fourier spectrum. In this paper, we describe a (1, N) phase shifting technique with fast Fourier transform (FFT) for non destructive evaluation (NDE) of quasi-dynamic behavior of objects subject to slowly varying loads. The prominent advantage of the technique is that, it requires only a single frame prior to the object deformation and N number of frames during the object deformation for NDE. Experimental results are presented on a honeycomb structure subjected to thermal load.

In this paper, an analytic procedure has been developed for the root cause identification of the lens module decentration. By analyzing the lens module according to a predetermined analysis process to generate analysis parameters corresponding to the lens module, and measured performance data can then be compared with these simulated data for validation. This can reveals very valuable information to help fine tune the injection mold.

In this work, the optical evaluation of a mechanism for space applications under vacuum and temperature controlled conditions at the facilities of the Space Instrumentation Laboratory (LINES) of the Aerospace Technical Nacional Institute of Spain (INTA) is reported. The mechanism was developed by the Spanish company SENER to fulfill the high performance requirements from ESA technology preparatory program for GAIA Astrometric Mission; in particular, a five degrees of freedom (dof), three translations and two rotations positioning mechanism for the secondary mirror of the GAIA instrument. Both interferometric tests and autocollimator measurements have been combined in order to extract the information about the accuracy of the mechanism movements as well as their repeatability under adverse environmental conditions: vacuum and thermal controlled conditions, up to a 10^-6mbar and 100K. The scope of this paper will cover the measurements concept selection, the presentation of verification activities, the results of such dedicated optical measurements, the correlation with the mechanical models and a brief description of the design process followed to meet the test requirements.

We present a method of aspheric surface profile measurement based on the principle of curvature sensor, which measures the curvature of subaperture topography along a line and then reconstructs the entire profile from the measured local curvature data. The subaperture topography is obtained by using white-light scanning interferomtery to avoid the optical alignment error along an optical axis. Test measurement results demonstrate that the proposed method and system is well suited for the aspheric surface profile measurement.

The wavefront reconstruction and uncertainty analysis of Hartmann-Shack wavefront sensor was demonstrated. In the simulation we analysis some kinds of tolerance in the wavefront sensor system and also calculate some uncertainty sources like focal length, pixel resolution, etc. And finally get the theoretical uncertainty of H-S wavefront sensor.

We report an approach for three-dimensional (3D) imaging with use of acousto-optic fringe projector (AOFP) and a technique of piecewise temporal phase unwrapping. The AOFP is controlled by direct digital synthesizer to generate a sequence of fringe patterns with different spatial frequencies so that encoding with variable sensitivity can be realized. Furthermore, we present a new phase unwrapping strategy for incremental phase reconstruction with the level of details. The algorithm is developed as a piecewise temporal phase unwrapping with a tolerance of deviation from the condition imposed upon conventional temporal phase unwrapping technique. Preliminary experiment results are given to support proposed approach.

At first, the paper carries on the stable state thermal analysis to the temperature field distribution of the drawing furnace, then, a rod-in-tube technique is described here to the fabrication of tellurite glass fiber. There are some equipments needed, which are designed according to the dimension of the fiber required. The different combinations of these equipment could meet the various requirements, such as the rotating equipment and drawing furnace under vacuum controlling, for the aim of fiber fabrication with high diameter ratio of cladding to core (DRCC) for single-mode optical fibers.

Phase detection is one of the most important processing steps in optical phase-shifting interferometry. It aims to reconstruct the phase field of wavefront from the interferogram. To solve this problem, many algorithms of phase detection have been proposed these years. Here, A FFT-based two-step phase shifting (TPS) algorithm is described in detail and implemented by use of experimental interferograms. This algorithm has been proposed to solve the TPS problem with random phase shift except π. By comparison with the Visibility-Function-based TPS algorithm, it proves that the FFT-based algorithm has obvious advantages in phase extracting. Meanwhile, we present a π-phase-shift supplement to the TPS algorithm, which combines the two interferograms and demodulates the phase map from a combined interferogram. So combining this quasi-two-step method and FFT-based one, one could really implement the TPS with random phase shift. Thereafter, we design an optical setup of two-channel TPS interferometer with random phase shift, which could capture the two interferograms simultaneously. At the same time, we propose a fringe-variable Jamin interferometer to detect reversed domain of ferroelectric crystal in real time. It could realize the two-step phase shifting with π radian.

Two-run-times-two-frame phase shift method is reviewed and a new phase retrieval algorithm is proposed. The properties of two phase retrieval algorithms are discussed from the point of view of Fourier analysis. Analysis shows that the two algorithms are equivalently sensitive to phase-shifter miscalibration and irreproducibility, and the amplitude of phase error depends on the average phase-step error. The influences of the signal harmonics on phase measurement rely on the phase shift of the object beam. The effects of random noise on the two algorithms are generally different, but the same only when the phase step of the reference beam is equal to Π/2.

Improvement of the linewidth and the mode-hop free tuning range of the Vertical Cavity Surface Emitting Laser (VCSEL) diode is the main goal of our upcoming Fiber Bragg Gratings (FBGs). The VCSEL with the fiber grating will be very suitable laser source for new generation of the absolute and the incremental laser interferometers based on our published VCSEL interferometer. The linewidth of the emission spectrum and the mode-hop free tuning range of the wavelength are critical in laser interferometry. The full width in half maximum (FWHM) linewidth of VCSEL at 760 nm wavelength is 100 MHz approximately. Tuning range up to 1 nm was measured by a highly precise commercial lambdameter with 0.1 pm resolution. To improve such a characteristic a high precise FBG must be selected. On the basis of our simulations and measurements of the commercially available fiber gratings we designed a special 100 mm long fiber Bragg grating with apodization. We expect the application of the FBG to improvement of the linewidth and mode-hop free tuning range of VCSEL at the wavelength 760 nm to increase resolution of laser interferometer based on VCSEL diode.

There are many cases when absolute measurements of objects with large height differences or height discontinuity is needed. These measurements can not be covered by classical interferometry since the range of non-ambiguity is limited to half the optical wavelength. Several techniques have been already developed for extending of non-ambiguity range. However most of them is based on multi-wavelength methods which demands expensive light sources and special environment conditions. In this work the new interferometric technique for absolute measurements of large steps discontinuities is proposed. Variable wavefront of the illuminating beam and special procedure for calibration of the measurement volume are used for extending of the measurement range without using multispectral sources. Additionally, calibration of the measurement area simplifies fringe processing and quicken measures. Theoretical analysis of this technique, its numerical simulations and experimental verification are presented and discussed.

The 'Zeeko Classic' polishing process is implemented in a series of CNC machine-tools. The standard tooling utilizes inflated membranes ('bonnet') covered with standard polishing cloths, and flooded by a supply of re-circulating polishing slurry. The usual input quality is a part off a precision CNC grinding machine, and the process both polishes and corrects form. In this paper we demonstrate how dynamic range can be substantially extended using three distinct Zeeko Grolishing processes that are hybrids between loose-abrasive polishing and bound-abrasive grinding. The output quality and volumetric removal rates of these processes are compared and contrasted. Finally, we note how these hybrid processes can extend the capabilities of the machine from polishing and form control, to smoothing parts with inferior input-quality, removing larger volumes of material during form control, and addressing harder materials.

ZEON CORPORATION developed innovative optical plastic Cyclo Olefin Polymer (COP), ZEONEX ^(R) with own technology in 1990 then started commercial production of ZEONEX^(R) for optical applications with its very unique properties such as high light transmission, low birefringence, low water absorption, and high glass-transition temperature etc. ZEONEX^(R) exhibits outstanding optical performance even under high humidity and temperature conditions. In order to meet increasing requirements of optical market, ZEON CORPORATION newly developed ZEONEX^(R)F52R which has high glass-transition temperature 156 deg. C and shows the feature of very low focal length change after high-temperature and high-humidity test.

High quality optical lenses are usually finished by magnetorheological finishing (MRF). In this process an abrasive fluid, with the ability to stiffen in a magnetic field, is used as the polishing tool in a computer-controlled machine tool. Although the machine is automated it is necessary for a skilled operator to set the machine and make judgments with regard to its operation. An investigation has been under way to examine the detailed operation of the MRF process, and the information that is necessary to establish best practice. This has resulted in the incorporation of a knowledge based system (KBS) into the machine control regime, and a methodology for the creation of artificial polishing tool characteristics, the machine influence function. The incorporation of the these elements has been instrumental in the operation of an enhanced MRF machine. This has been subject to extensive test procedures, and it has been demonstrated that the production process may be enhanced significantly and consistently. Batch production time may be significantly reduced, a figure in excess of a 50% reduction was met consistently during prolonged operation. Furthermore the incorporation of the KBS is instrumental in increasing the automation of the MRF process, reducing the levels of manual input necessary to manage machine operation.