High-resolution measurement of internal interface of optically transparent materials
Author(s):
Chun-Wei Chang;
I-Jen Hsu
Show Abstract
The measurement of surface morphology of a material with high resolution is important in both the industrial and
biomedical applications. Furthermore, a precise measurement of the morphology of the internal interface is usually
needed for materials with multilayered structures. Although some optical techniques can provide subsurface imaging of
materials, their resolutions are difficult to achieve nanometer scale. In our research, an optical system based on a
composite interferometer which can image the internal interface of a material with nanometer resolution is proposed and
demonstrated. The system consists of a Michelson interferometer and a Mach-Zehnder interferometer. The Michelson
interferometer with a broadband light source is used for three-dimensional imaging of the sample. In the Mach-Zehnder
interferometer, a prism and a retro-reflector are arranged for an optical delay line with adjustable length. The two
interferometers share common light source and a rapid scanning optical delay system used for axial scanning. In the
experiment, the adjustable optical delay line in the second interferometer is adjusted for the optical path lengths to match
that relative to the interface under investigation. With a phase compensation mechanism, the interface can be imaged
with an axial accuracy at nanometer scale.
Microfluidic design and fabrication of wafer-scale varifocal liquid lens
Author(s):
Jeong-Yub Lee;
Seung-Tae Choi;
Seung-Wan Lee;
Woonbae Kim
Show Abstract
Microfluidic design and fabrication was developed for wafer-scale varifocal liquid lens which is slim less than 0.9mm.
The liquid-filled varifocal lens has advanced functions such as auto macro and focusing to obtain a high quality of
image. This varifocal lens is similar to human eye and it consists of main Si frame which has penetrated inner hole,
upside-bonded PDMS (polydimethylsiloxane) elastomer membrane, downside-bonded glass plate and optical fluid
confined by these structures. Si frame, which has a circular hole for tunable lens chamber, several holes for actuator
chamber and micro-fluidic channels between chambers, is fabricated using thin Si wafer and microelectromechanical
system (MEMS) processes. When optical fluid is filled the internal cavity by conventional injection, void trapping which
degrades optical performance or filling impossibility happens because of high aspect ratio between lens diameter and
thickness for slim liquid lens. To prevent these problems, we developed wafer-based microfabrications of seal line
dispensing, accurate dropping of optical fluid, pressing & bonding process in vacuum and UV sealant curing. Afterward,
electro-active polymer actuators, which push the optical fluid to change the lens shape, was attached on the PDMS
membrane of liquid lens wafer and sawing process of 9.4mm*9.0mm chip size followed. Finally, the varifocal liquid
lens which is slim less than 0.6mm thickness (0.9mm included actuators), tunable more than 20diopter changes of
refractive power, guaranteed reliability of 300,000 repetitions and suitable for mass production, was realized.
Fabrication and characterization of polymer based spatial light modulators
Author(s):
G. Ouyang;
K. Wang;
M. N. Akram;
X. Chen
Show Abstract
We report on device properties of tunable spatial light modulators for high-resolution optical applications by a novel
fabrication process. Thin polydimethylsiloxane (PDMS) films (4ìm-13ìm) were sandwiched between a flexible gold
film(50nm) and a rigid substrate with a comb-like electrode either by compression molding or spin coating. By applying
voltage between the upper gold film and underlying electrode, the initial plane PDMS surface changes into a form of
grating. Far-field scattering pattern with high order light components was observed by illumination at the continuously
reflective gold film with laser beam. Characterization was done by measuring the grating profile of the PDMS and the
response time. The PDMS deformation was demonstrated to increase with driving voltage. The deformation for 6ìm
thick PDMS is measured around 100nm when driving voltage is applied as 230V. Modeling and simulation of the
modulator electro-mechanical behavior was done for varies structure design. The simulation results showed fair
agreement with the experimental results. The response time, which defines how fast the PDMS response to the applied
voltage, was measured as a function of the driving voltage. The measured rise time is around 1 micorseconds and the fall
time is around 0.2 microseconds.
Comparison of freeform manufacturing techniques in the production of monolithic lens arrays
Author(s):
Gregg E. Davis;
Jeffrey W. Roblee;
Alan R. Hedges
Show Abstract
Monolithic lens arrays are used in applications such as hyper-spectral imaging, Shack-Hartmann wavefront sensors, and
lens replication molds, where lens-to-lens registration is critical. Traditionally, monolithic lens arrays are produced by
diamond turning one lens at a time on axis. This process requires the substrate to be shifted to a new position before the
next lens is machined. This intermediate step increases production time and makes it difficult to achieve lens-to-lens
registration accuracy. Freeform diamond machining allows lens arrays to be produced in a single setup. Since there are
no intermediate shifts of the substrate, the lens-to-lens registration is inherent to the program and machine accuracy. The
purpose of this paper is to compare different freeform manufacturing processes in the production of a three-element
germanium lens array. Freeform machining technologies including Slow Tool Servo (STS), Fast Tool Servo (FTS) and
Diamond Micro-Milling (DMM) will be used to produce this lens array. The results for process times, figure, and finish
characteristics will be compared across all three techniques.
Nanometer level freeform surface measurements with the NANOMEFOS non-contact measurement machine
Author(s):
Rens Henselmans;
Lennino Cacace;
Geerten Kramer;
Nick Rosielle;
Maarten Steinbuch
Show Abstract
Applying aspherical and freeform optics in high-end optical systems can improve system performance while decreasing
the system mass, size and number of required components. The NANOMEFOS measurement machine is capable of
universal non-contact and fast measurement of aspherical and freeform optics up to ∅500 mm, with an uncertainty of 30
nm (2σ). In this machine, the surface is placed on a continuously rotating air bearing spindle, while a specially developed
optical probe is positioned over it by a motion system. A separate metrology system measures the probe and product
position relative to a metrology frame.
The prototype realization, including custom electronics and software, has been completed. The noise level at standstill is
0.88 nm rms. A reference flat was measured with 13 μm and 0.73 mm tilt. Both measurements show an rms flatness of
about 8 nm rms, which correspond to the NMi measurement. A hemisphere has also been measured up to 50° slope, and
placed 0.2 mm eccentric on the spindle. These measurements reproduce to about 5 nm rms. Calibration and software are
currently being improved and the machine is applied in TNO aspherical and freeform optics production.
Accuracy of freeform manufacturing processes
Author(s):
G. P. H. Gubbels;
B. W. H. Venrooy;
R. Henselmans
Show Abstract
The breakthrough of freeform optics is limited by manufacturing and metrology technology. However, today's
manufacturing machines like polishing robots and diamond turning machines are accurate enough to produce good
surface quality, so the question is how accurate can a freeform be produced. To investigate how accurate freeform optics
can be diamond turned, measurable freeforms (e.g. an "off-axis" sphere) were diamond turned and they were compared
to there on-axis equivalents. The results of this study are described in this paper. Furthermore, an overview of the
accuracies of freeform optics that TNO diamond turned are presented. An indication of freeform accuracy for diamond
turned optics is derived from this, which can be used for optical designers as a guideline in their design work.
Ultraprecision machining techniques for the fabrication of freeform surfaces in highly integrated optical microsystems
Author(s):
Sebastian Stoebenau;
Stefan Sinzinger
Show Abstract
The application of multi-axis micromilling and flycutting is investigated for the fabrication of complex optical microsystems
incorporating different classes of aspherical and freeform optical elements. Such elements provide the necessary
degrees of freedom for aberration correction in integrated optical microsystems and are specifically interesting for
applications like beam shaping or computational imaging. Especially for elements with small radii of curvature, high
aspect ratios and spatial frequencies, micromilling and flycutting are interesting alternatives to the more established
diamond turning technology. We present the results of the fabrication of a monolithically integrated optical microsystem
consisting of two tilted flat surfaces used as coupling prisms and a freeform imaging element. On the resulting surfaces
the average roughness height without subsequent polishing was found to be Ra = 18.2 ... 25.5 nm (depending on the
fabrication technique) with an overall shape accuracy < 0.5 ... 2.9 μm (based on the determination of the radii of
curvature).
Increased UV transmission by improving the manufacturing processes for FS
Author(s):
Jessica DeGroote-Nelson;
Tobias Nitzshe;
Daniel E. Savage;
Jonathan T. Watson;
Donald K. Henry;
Andrew A. Haefner;
Robert A. Wiederhold
Show Abstract
Optical designers have been designing ultraviolet (UV) systems at wavelengths in the UV region for many
years. With increasing demand for deep UV applications, special considerations that are not applicable to traditional
visible optics must be taken to produce the optics. Specifically as the wavelength of incident light decreases, the
importance of very smooth surfaces increases. The intent of this project is to increase the performance of UV optics
in a four-phase project. The first phase consists of characterizing sub-surface damage using destructive methods to
enable process control, the second phase (presented here) focuses on polishing methods, the third phase will include
cleaning and possible etching protocols and the fourth phase will be improving thin film coating performance.
Varying electro-kinetic interactions to achieve predictable removal rates and smooth surfaces on ZnS
Author(s):
Jessica DeGroote-Nelson;
Jarrett A. Drucker;
Andrew A. Haefner;
Robert A. Wiederhold
Show Abstract
A conventional polishing study was conducted with infrared material zinc sulfide with the goal of producing defect-free
polished surfaces in predictable amounts of time. Utilizing the measured electro-kinetic properties of the zinc sulfide
and polishing abrasives, polishing slurries were selectively altered and the resulting removal rates and surface roughness
values were measured. This paper will serve as a baseline for developing an empirical model for optimizing both
surface roughness and removal rate for two different types of abrasives and two pitch types with ZnS.
Zirconia coated carbonyl iron particle-based magnetorheological fluid for polishing
Author(s):
Shai N. Shafrir;
Henry J. Romanofsky;
Michael Skarlinski;
Mimi Wang;
Chunlin Miao;
Sivan Salzman;
Taylor Chartier;
Joni Mici;
John C. Lambropoulos;
Rui Shen;
Hong Yang;
Stephen D. Jacobs
Show Abstract
Aqueous magnetorheological (MR) polishing fluids used in magnetorheological finishing (MRF) have a high solids
concentration consisting of magnetic carbonyl iron particles and nonmagnetic polishing abrasives. The properties of MR
polishing fluids are affected over time by corrosion of CI particles. Here we report on MRF spotting experiments
performed on optical glasses using a zirconia coated carbonyl iron (CI) particle-based MR fluid. The zirconia coated
magnetic CI particles were prepared via sol-gel synthesis in kg quantities. The coating layer was ~50-100 nm thick,
faceted in surface structure, and well adhered. Coated particles showed long term stability against aqueous corrosion.
"Free" nano-crystalline zirconia polishing abrasives were co-generated in the coating process, resulting in an abrasivecharged
powder for MRF. A viable MR fluid was prepared simply by adding water. Spot polishing tests were performed
on a variety of optical glasses over a period of 3 weeks with no signs of MR fluid degradation or corrosion. Stable
material removal rates and smooth surfaces inside spots were obtained.
Normal force and drag force in magnetorheological finishing
Author(s):
Chunlin Miao;
Shai N. Shafrir;
John C. Lambropoulos;
Stephen D. Jacobs
Show Abstract
The material removal in magnetorheological finishing (MRF) is known to be controlled by shear stress, λ, which equals
drag force, Fd, divided by spot area, As. However, it is unclear how the normal force, Fn, affects the material removal in
MRF and how the measured ratio of drag force to normal force Fd/Fn, equivalent to coefficient of friction, is related to
material removal. This work studies, for the first time for MRF, the normal force and the measured ratio Fd/Fn as a function
of material mechanical properties. Experimental data were obtained by taking spots on a variety of materials including
optical glasses and hard ceramics with a spot-taking machine (STM). Drag force and normal force were measured with a
dual load cell. Drag force decreases linearly with increasing material hardness. In contrast, normal force increases with
hardness for glasses, saturating at high hardness values for ceramics. Volumetric removal rate decreases with normal force
across all materials. The measured ratio Fd/Fn shows a strong negative linear correlation with material hardness. Hard
materials exhibit a low "coefficient of friction". The volumetric removal rate increases with the measured ratio Fd/Fn which
is also correlated with shear stress, indicating that the measured ratio Fd/Fn is a useful measure of material removal in MRF.
Contributions of nanodiamond abrasives and deionized water in magnetorheological finishing of aluminum oxynitriden
Author(s):
Chunlin Miao;
John C. Lambropoulos;
Henry Romanofsky;
Shai N. Shafrir;
Stephen D. Jacobs
Show Abstract
Magnetorheological finishing (MRF) is a sub-aperture deterministic process for fabricating high-precision optics by
removing material and smoothing the surface. The goal of this work is to study the relative contribution of
nanodiamonds and water in material removal for MRF of aluminum oxynitride ceramic (ALON) based upon a
nonaqueous magnetorheological (MR) fluid. Removal was enhanced by a high carbonyl iron concentration and the
addition of nanodiamond abrasives. Small amounts of deionized (DI) water were introduced into the nonaqueous MR
fluid to further influence the material removal process. Material removal data were collected with a spot-taking machine.
Drag force (Fd) and normal force (Fn) before and after adding nanodiamonds or DI water were measured with a dual load
cell. Both drag force and normal force were insensitive to the addition of nanodiamonds but increased with DI water
content in the nonaqueous MR fluid. Shear stress (i.e., drag force divided by spot area) was calculated, and examined as
a function of nanodiamond concentration and DI water concentration. Volumetric removal rate increased with increasing
shear stress, which was shown to be a result of increasing viscosity after adding nanodiamonds and DI water. This work
demonstrates that removal rate for a hard ceramic with MRF can be enhanced by adding DI water into a nonaqueous MR fluid.
Simulation and analysis of the polishing process for aspheres
Author(s):
Andreas Kelm;
Manuel Hänle;
Rainer Boerret;
Stefan Sinzinger
Show Abstract
For the Computer Controlled Polishing (CCP) process of aspheres and freeform shapes different kind of subaperture
tools can be used. The selection of the best tool out of a wide range of possible and available tools is today based on the
experience of the skilled operator. If the optical part is finished with sufficient quality in a reasonable time, the working
procedure is fixed. Another approach is to put the tool choice on a scientific base, using a simulation to generate the
wear function and a Power Spectral Density (PSD) analysis to describe the residual shape deviations. Based only on
theoretical tool data and the geometric shape of the tool, the final result of the shape correction could be calculated and
transferred to a NC machine code for various polishing machines.
Edge tool influence function library using the parametric edge model for computer controlled optical surfacing
Author(s):
Dae Wook Kim;
Won Hyun Park;
Sug-Whan Kim;
James H. Burge
Show Abstract
Computer controlled optical surfacing (CCOS) requires accurate knowledge of the tool influence function (TIF) for the
polishing tool. The linear Preston's model for material removal has been used to determine the TIF for most cases. As
the tool runs over the edge of the workpiece, however, nonlinear removal behavior needs to be considered to model the
edge TIF. We reported a new parametric edge TIF model in a previous paper.** This model fits 5 parameters to
measured data to accurately predict the edge TIF. We present material from the previous paper, and provide a library of
the parametric edge TIFs for various tool shape and motion cases. The edge TIF library is a useful reference to design an
edge figuring process using a CCOS technique.
Calculating BRDFs from surface PSDs for moderately rough optical surfaces
Author(s):
James E. Harvey;
Narak Choi;
Andrey Krywonos;
Jesus Grasa Marcen
Show Abstract
Image degradation due to scattered radiation is a serious problem in many short wavelength
(X-ray/EUV) imaging systems. Most currently-available image analysis codes require the scatter
behavior (BRDF data) as input in order to calculate the image quality from such systems. This BRDF
data is difficult to measure and rarely available for the operational wavelengths of interest. Since the
smooth-surface approximation is often not satisfied at these short wavelengths, the classical
Rayleigh-Rice expression that indicates the BRDF is directly proportional to the surface PSD cannot be
used to calculate BRDFs from surface metrology data for even slightly rough surfaces. We discuss the
implementation of an FFTLog numerical Hankel transform algorithm that enables the practical use of
the computationally intensive Generalized Harvey-Shack (GHS) surface scatter theory. The FFTLog
Hankel transform algorithm is validated over the large dynamic range of relevant spatial frequencies
required for short wavelength imaging applications, and BRDFs are calculated and displayed for
increasingly short wavelengths that violate the smooth surface approximation implicit in the
Rayleigh-Rice surface scatter theory.
Swing-arm optical CMM for aspherics
Author(s):
Peng Su;
Chang Jin Oh;
Robert E. Parks;
James H. Burge
Show Abstract
A profilometer for in situ measurement of the topography of aspheric mirrors called the Swing arm Optical CMM (SOC)
was built, and has been used for measuring the figure of 1.4 m convex aspheric mirrors with a performance rivaling full
aperture interferometric tests. Errors in the SOC that have odd symmetry are self-calibrated due to the test geometry.
Even errors are calibrated against a full aperture interferometric test.
Manufacturing and performance test of a 800 mm space optic
Author(s):
Matthias R. Krödel;
Tsuyoshi Ozaki;
Masami Kume;
Yukari Y. Yui;
Hiroko Imai;
Haruyoshi Katayama;
Yoshio Tange;
Takao Nakagawa
Show Abstract
Next generation space telescopes, which are currently being developed in the US and Europe, require large-scale lightweight
reflectors with high specific strength, high specific stiffness, low CTE, and high thermal conductivity. To meet
budget constraints, they also require materials that produce surfaces suitable for polishing without expensive overcoatings.
HB-Cesic® - a European and Japanese trademark of ECM - is a Hybrid Carbon-Fiber Reinforced SiC composite
developed jointly by ECM and MELCO to meet these challenges. The material's mechanical performance, such as
stiffness, bending strength, and fracture toughness are significantly improved compared to the classic ECM Cesic®
material (type MF). Thermal expansion and thermal conductivity of HB-Cesic® at cryogenic temperatures are now
partly established; and excellent performance for large future space mirrors and structures are expected.
This paper will present the whole manufacturing process of such a space mirror starting from the raw material
preparation until the polishing of the optic including cryo testing .
The letters "HB" in HB-Cesic® stand for "hybrid" to indicate that the C/C raw material is composed of a mixture of
different types of chopped, short carbon-fibers.
Fabrication and testing of 1.4-m convex off-axis aspheric optical surfaces
Author(s):
James H. Burge;
S. Benjamin;
D. Caywood;
C. Noble;
M. Novak;
C. Oh;
R. Parks;
B. Smith;
P. Su;
M. Valente;
C. Zhao
Show Abstract
New developments in fabrication and testing techniques at the College of Optical Sciences, University of Arizona have
allowed successful completion of 1.4-m diameter convex off-axis aspherics. The optics with up to 300 μm aspheric
departure were finished using a new method of computer controlled polishing and measured with two new optical tests:
the Swingarm Optical CMM (SOC) and a Fizeau interferometer using a spherical reference surface and CGH correction.
This paper shows the methods and equipment used for manufacturing these surfaces.
Non-null interferometric aspheric testing with partial null lens and reverse optimization
Author(s):
Dong Liu;
Yongying Yang;
Yongjie Luo;
Chao Tian;
Yibing Shen;
Yongmo Zhuo
Show Abstract
With respect to null test, non-null test is more flexible and can provide fast, general test with acceptable accuracy. A
non-null interferometric aspheric testing system, which employs partial null lens and reverse optimization
reconstruction, is proposed. The partial null lens compensates most of the longitude aberration of the aspheric under test
and keeps the slope of the non-null wavefront within the resolution of the detector. The reverse optimization
reconstruction procedure reduces the retrace error of the non-null test and reconstructs the figure of the test aspheric. The
characteristic, design process of the partial null lens and especially the implement of the reverse optimization
reconstruction are discussed in detail. Computer simulation shows the reverse optimization reconstruction procedure can
reconstruct the aspheric figure error with an accuracy better than 1/200wave within 5 mins. The error analysis is also
considered and some conclusions are given. This research is of great importance for general aspheric surfacing and testing.
Verification procedure for the wavefront quality of the primary mirrors for the MRO interferometer
Author(s):
Eric J. Bakker;
Andres Olivares;
Reed A. Schmell;
Rodney A. Schmell;
Darren Gartner;
Anthony Jaramillo;
Kelly Romero;
Andres Rael;
Jeff Lewis
Show Abstract
We present the verification procedure for the 1.4 meter primary mirrors of the Magdalena Ridge Observatory
Interferometer (MROI). Six mirrors are in mass production at Optical Surface Technologies (OST) in Albuquerque.
The six identical parabolic mirrors will have a radius of curvature of 6300 mm and a final surface wavefront quality of
29 nm rms.
The mirrors will be tested in a tower using a computer generated hologram, and the Intellium™ H2000 interferometer
from Engineering Synthesis Design, Inc. (ESDI). The mirror fabrication activities are currently in the early stage of
polishing and have already delivered some promising results with the interferometer. A complex passive whiffle tree
has been designed and fabricated by Advanced Mechanical and Optical Systems (AMOS, Belgium) that takes into
account the gravity loading for an alt-alt mount. The final testing of the primary mirrors will be completed with the
mirror cells that will be used in the telescopes.
In addition we report on shear tests performed on the mirror cell pads on the back of the primary mirrors. These pads are
glued to the mirror. The shear test has demonstrated that the glue can withstand at least 4.9 kilo Newton. This is within
the requirements.
Monolithic versus segmented primary mirror concepts for space telescopes
Author(s):
Stephen E. Kendrick
Show Abstract
A number of ongoing astrophysical mission concept studies are based on large aperture spaceborne telescopes. As optics
get larger, both manufacturing and engineering trades come into consideration and must be balanced with the science
goals and requirements. One of the top-level telescope trades examines the impact of a large monolithic primary mirror
versus an array of smaller mirror segments to either fully or sparsely populate the same aperture. The first consideration
is the scientific impact. Should the scattered edge effects and diffraction of a segmented design be acceptable, it then
becomes a fabrication, test, and cost trade along with any associated risks. This paper will examine some of the key
factors that go into such a trade and looks at manufacturing breakpoints. Examples such as the 4-m aperture New World
Observer (NWO) and the 8-m aperture Advanced Technology Large Aperture Space Telescope (ATLAST) will be presented.
Measurement of high-departure aspheric surfaces using subaperture stitching with variable null optics
Author(s):
Paul Murphy;
Gary DeVries;
Jon Fleig;
Gregory Forbes;
Andrew Kulawiec;
Dragisha Miladinovic
Show Abstract
Aspheric surfaces can provide significant benefits to optical systems, but manufacturing high-precision
aspheric surfaces is often limited by the availability of surface metrology. Traditionally, aspheric measurements have
required dedicated null correction optics, but the cost, lead time, inflexibility, and calibration difficulty of null optics
make aspheres less attractive. In the past three years, we have developed the Subaperture Stitching Interferometer for
Aspheres (SSI-A®) to help address this limitation, providing flexible aspheric measurement capability up to 200 waves
of aspheric departure from best-fit sphere.
Some aspheres, however, have hundreds or even thousands of waves of departure. We have recently
developed Variable Optical Null (VONTM) technology that can null much of the aspheric departure in a subaperture. The
VON is automatically reconfigurable and is adjusted to nearly null each specific subaperture of an asphere. The VON
provides a significant boost in aspheric measurement capability, enabling aspheres with up to 1000 waves of departure
to be measured, without the use of null optics that are dedicated to each asphere prescription. We outline the basic
principles of subaperture stitching and the Variable Optical Null, demonstrate the extended capability provided by the
VON, and present measurement results from our new Aspheric Stitching Interferometer (ASITM).
Stitching interferometry: the practical side of things
Author(s):
Michael Bray
Show Abstract
Stitching Interferometry is now commonplace in Large Optics workshops. However, this technique is far more difficult
to implement than might appear at first sight. More precisely, because stitching involves multiple overlapping
measurements, there is huge potential for measurement error amplification. And, because there is usually no element of
comparison, finding and correcting error sources is usually tricky. This has brought us to develop error detection and/or
correction tools in our Stitching Software, two of which will be discussed and graphically illustrated here:
First: Environment stability analysis, including computation of stitching measurements probable fluctuations. This requires
no mechanical stage, and can therefore be performed as a preliminary test.
Second: Calibration error is often a limiting factor. We have solved this issue, for the 1D case, using the same hardware
as that used by the stitching process, and requiring no handling of the component. The 2D case is currently being developed.
In this paper, we show results obtained from real measurements performed at Customers' facilities: The graphical
stability outputs are very instructive, and the self-calibration technique performs remarkably well.
Research of precision interference locating method for a partial null compensator at aspheric testing
Author(s):
Yongying Yang;
Dong Liu;
Gao Xin;
Chao Tian;
Yongjie Luo;
Yibing Shen;
Yongmo Zhuo
Show Abstract
Based on the difference between theoretical with real interferogram images the figure of original aspheric surface can be
obtained using an algorithm of Reverse iterate Optimization Reconstruction (ROR) calculating technique. Because the
procedure of ray tracing path needed an accurate geometry of optical structure size so the aspheric and compensator LC must be located in the optical path. To avoid the compensator LC resulted in bigger spherical aberration a smart located method is proposed in this paper. Before measurement an aplanatic lens consists of compensator LC and another
removable lens LM that the last surface is a standard one. So Fiezau interference is formed by the standard one with reflected ray from the vertex of aspheric that the aspheric surface detected can be accurately located. At testing the
lenses LM will be removed and the aspheric is moved to an adapted position. The experiments show the displacement locating accuracy is an amount of micron. The RMS for aspheric testing of ROR calculating technique is better than 1/200 wavelength.
Fizeau interferometer with spherical reference and CGH correction for measuring large convex aspheres
Author(s):
M. B. Dubin;
P. Su;
James H. Burge
Show Abstract
Large, convex surfaces, such as secondary mirrors, have presented challenging metrology problems for many years.
Over the years, new metrology approaches have been developed to keep pace with the ever changing definition of
"large". The latest class of large secondary mirrors requires a new approach that is practical, scalable and can produce
low uncertainty measurements. This paper presents a new configuration that uses a computer generated hologram based
Fizeau interferometer to make sub-aperture measurements on large secondary mirrors. One of the key features of this
system is that all of the surfaces used in the interferometer are spherical. Another key element is the ability to perform
simultaneous phase shift interferometry which reduces sensitivity to vibration. An example system that is capable of
measuring the Large Synoptic Survey Telescope secondary mirror is presented along with a sensitivity analysis.
Limits for interferometer calibration using the random ball test
Author(s):
Ping Zhou;
James H. Burge
Show Abstract
The random ball test (RBT), also known as the CaliBall test, is often used to calibrate interferometer transmission
spheres. This paper provides a way to estimate the total errors remaining after interferometer calibration using the
RBT. Errors that cannot be removed by calibration include random errors due to measurement noise in the calibration,
geometric errors, and errors due to diffraction. The random errors can be reduced by averaging multiple random ball
tests. The geometric errors and diffraction errors are systematic, and arise when the radius of the CaliBall is different
from that of the test optic.
Orthonormal vector polynomials in a unit circle, application: fitting mapping distortions in a null test
Author(s):
Chunyu Zhao;
James H. Burge
Show Abstract
We developed a complete and orthonormal set of vector polynomials defined over a unit circle. One application of these
vector polynomials is for fitting the mapping distortions in an interferometric null test. This paper discusses the source of
the mapping distortions and the approach of fitting the mapping relations, and justifies why the set of vector polynomials
is the appropriate choice for this purpose. Examples are given to show the excellent fitting results with the polynomials.
Scanning pentaprism measurements of off-axis aspherics II
Author(s):
Peng Su;
James H. Burge;
Brian Cuerden;
Richard Allen;
Hubert M. Martin
Show Abstract
The scanning pentaprism test has provided an important absolute test method for flat mirrors, parabolic mirrors and also
collimation systems. We have developed a scanning pentaprism system to measure off-axis paraboloidal mirrors such as
those for the Giant Magellan Telescope (GMT) primary mirror. Special characteristics of the pentaprism testing of an
off-axis mirror are discussed in the paper. We provide performance results for the final measurement of a 1.7 m off-axis
parabolic mirror and present a technique used to determine the radius of the parent, off-axis distance and the clocking of
the mirror from the data from the scanning pentaprism system.
Imaging analysis of a novel compound diffractive telescope system
Author(s):
Jinying Yue;
Zhenwu Lu;
Hua Liu;
Wenbin Xu;
Hongxin Zhang;
Hu Zhang;
Ying Liu
Show Abstract
The main feature of the compound diffractive telescope is the combination of diffractive optics with compound structure
arranged eyepieces. In this paper, a design of the compound diffractive telescope is firstly introduced, and a 4.2° FOV
is obtained with one primary lens and twenty-one eyepieces. Secondly, image characteristic of different channels is
analyzed with the design wavelength in ASAP, and one modified phase function model of diffractive optical element is
introduced to analyze the MTF curves for 0° FOV, which provides a more accurate prediction of the performance of the
system. Then the system is tested by the star image test, and the diffraction limit images are got within ± 2° FOV. And
finally, two pictures taken from the adjacent FOV proved to be able to be spliced together. All the results above
demonstrate that a good performance of the compound diffractive telescope.
High-speed and precision auto-focusing system for direct laser lithography
Author(s):
Dong-Ik Kim;
Hyug-Gyo Rhee;
Jae-Bong Song;
Yun-Woo Lee
Show Abstract
The auto-focusing is one of the important parts in the automated vision inspection or measurement using optical
microscopes. Moreover, laser micromachining or laser lithography requires a high speed and precision auto-focusing. In
this paper, we propose and realize an auto-focusing system using two cylindrical lenses, which is the enhanced version of
the previous astigmatism method. It shows very good performances, especially very high speed and the largest
defocusing range in comparison with the previous astigmatic methods. The performance of our auto-focusing system was
evaluated by tracing the linear stage whose position was monitored by a commercial laser interferometer.
Development of a large ion beam figuring facility for correction of optics up to 1.7 m diameter
Author(s):
M. Ghigo;
S. Cornelli;
R. Canestrari;
D. Garegnani
Show Abstract
In the INAF-Astronomical Observatory of Brera (INAF-OAB) a new Ion Beam Figuring Facility, that adds to the
previous one, is under advanced construction. The present facility is able to figure optics up to 50 cm in diameter
meanwhile the new one is larger and will be able to figure optics up to 1.7 meter. It will employ a Kaufman Ion Source
having three degrees of freedom (x-y-z) with step motors and encoders. The source will have two different grid sizes so
to be able to figure the optics wit a broad or small removal function depending from the application. The control system
will be computer controlled and designed to be autonomous and self-monitoring during the figuring by using a
proprietary process control software. This software will use a time matrix map indicating the dwell times required for
each pixel of the optical surface. The software and the mathematical tools used to compute the Time Matrix solution has
been developed in INAF-OAB as well.
Laser tracker surface measurements of the 8.4m GMT primary mirror segment
Author(s):
Tom L. Zobrist;
James H. Burge;
Hubert M. Martin
Show Abstract
We have developed a metrology system that is capable of measuring rough ground and polished surfaces alike, is nearly
independent of the nominal surface shape, and can accommodate surfaces up to 8.4 m in diameter. The system couples a
commercial laser tracker with an advanced calibration technique and a system of external references. This system was
built to guide loose abrasive grinding and initial polishing of the off-axis primary mirror segments for the Giant
Magellan Telescope, and will be used to guide the fabrication of the Large Synoptic Survey Telescope primary and
tertiary mirrors as well. The results obtained using this system during the fabrication of the first segment of the Giant
Magellan Telescope are presented along with an assessment of the expected system accuracy.
Experimental investigation of the dimensions and quality of laser-drilled holes in metals
Author(s):
Mihai Stafe;
Constantin Negutu;
Ionut Vladoiu;
Adrian N. Ducariu;
Ion M. Popescu
Show Abstract
We investigated the process of laser micro-drilling of copper and iron by using nanosecond laser-pulses at 532nm
wavelength in atmospheric air. We analyzed the ablated volume, ablation rate, crater diameter, and craters quality as
functions of laser-fluence and beam-diameter. The fluence was varied between 10 and 6000 J/cm2 by changing the laserenergy.
The results indicate that the ablated volume increases linearly with fluence, whereas the ablation rate and crater
diameter increase linearly with the fluence's square root. The ablated volume, ablation rate, and crater diameter, increase
with thermal diffusivity of the materials. Additionally, the ablation threshold-fluence is demonstrated to be directly
related to the optical penetration depth.
The ablated volume, ablation rate, and crater diameter were further assessed for beam-diameters in the range of
10-50 microns by translating the targets away from the focal plane while keeping a constant fluence. The results indicate
that the ablated volume increases linearly with beam-diameter, whereas the ablation rate and crater diameter increase
linearly with the inverse of the beam-diameter's square root.
To investigate the craters quality we measured the dimension of the thermally affected zone (TAZ) around the
craters as a function of fluence. At fluences up to 400 J/cm2, where strong ionization occurs within the plume, the crater
diameter is <15 microns (comparable with beam diameter) and there is small TAZ around the craters. Further increase of
the fluence leads to a significant increase of TAZ, indicating that the expanding plasma plays a major role in metals
ablation in this fluence domain.
Parametric and scattering characterization of PDMS membranes for optical applications
Author(s):
A. Santiago-Alvarado;
S. Vazquez Montiel;
J. Munoz-Lopez;
J. Castro-Ramos;
J. A. Delgado Atencio
Show Abstract
Today elastic membranes are being used more frequent as optical surfaces in the science or in the industry. This
due to the advantages that they display in their handling and in their cost of production. These characteristics
make them ideals to apply them in micro-optical components and Tunable Focus Liquid Filled Length Lens
(TFLFLL). In order to know if a membrane of PDMS (PDMS Sylgard 184) is feasible for a specific application
within the field of the optics, it is necessary to know its mechanical, optical and chemical properties. In this
work the parametric membrane characterization is reported for an optical application. An important factor in
the performance of these membranes is related with their scattering factor that is produced due to the roughness
and impurities (micro-bubbles or dust particles). These membranes are used as refractive surface in TFLFLL. Experimental results of the characterization process and device performance are presented.
Modified alignment CGHs for aspheric surface test
Author(s):
Jae-Bong Song;
Ho-Soon Yang;
Hyug-Gyo Rhee;
Yun-Woo Lee
Show Abstract
Computer Generated Holograms (CGH) for optical test are commonly consisted of one main pattern for testing aspheric
surface and some alignment patterns for aligning the interferometer, CGH, and the test optics. To align the CGH plate
and the test optics, we designed the alignment CGHs modified from the cat's eye alignment method, which are consisted
of a couple of CGH patterns. The incident beam passed through the one part of the alignment CGH pattern is focused
onto the one radius position of the test aspheric surface, and is reflected to the other part, and vice versa. This method has
several merits compared to the conventional cat's eye alignment method. First, this method can be used in testing optics
with a center hole, and the center part of CGH plate can be assigned to the alignment pattern. Second, the alignment
pattern becomes a concentric circular arc pattern. The whole CGH patterns including the main pattern and alignment
patterns are consisted of only concentric circular fringes. This concentric circular pattern can be easily made by the polar
coordinated writer with circular scanning. The required diffraction angle becomes relatively small, so the 1st order
diffraction beams instead of the 3rd order diffraction beam can be used as alignment beams, and the visibility can be
improved. This alignment method also is more sensitive to the tilt and the lateral shift of the test aspheric surface. Using
this alignment pattern, a 200 mm diameter F/0.5 aspheric mirror and a 600 mm diameter F/0.9 mirror were tested.