This PDF file contains the front matter associated with SPIE Proceedings Volume 6676, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.
Tolerancing can be done with three different methods: using differential equations, using exact calculations and using the Monte-
Carlo technique. Thanks to the possibilities offered by modern computations, what is called integrated engineering using the
Microsoft Windows Component Object Model (COM), it is now possible to use different softwares to make the calculations,
collect the results and produce synthetic tables and figures which are quickly and clearly interpretable. This is possible with optical
design softwares implementing the Application Programming Interface (API).
Lenses for cameraphones are recent examples in which tolerancing is difficult. In order to take right decisions in choosing the
tolerances, we have been using the three methods for tolerancing. We are using this example to compare the results obtained.
Precision lens centering is necessary to obtain the maximum performance from a centered lens system. A technique
to achieve precision centering is presented that incorporates the simultaneous viewing through the upper lens surface
of the centers of curvature of each element as it is assembled in a lens barrel. This permits the alignment of the
optical axis of each element on the axis of a precision rotary table which is taken as the axis of the assembly.
Tolerancing of illumination systems is currently a difficult task, especially for components that are injection molded. The ISO standards are not applicable to such systems due to their innate requirements of image formation. Methods to parameterize the shape of injection-molded optical components are presented. First, a method based on experimental measurement of actual components is presented. Next, this method is extended to the Monte Carlo formation of perturbed parts based upon these measurements. Finally, a method based on the application of a bi-directional surface distribution function (BSDF), i.e., scatter profile, is based upon ray-trace results from the application of the experimental measurements. The BSDF method is fit with the ABg scatter function, applied to witness sample surfaces, and compared to the perturbation method. The utility of these two methods is presented, whereby the BSDF method is appropriate for systems with many ray-surface interactions, while the perturbation method is best suited for systems with limited ray-surface interactions.
Optical design and analysis software codes usually have built-in capabilities for performing rapid tolerance studies
on optical systems. However, these built-in capabilities often work on only a few selected performance metrics, such as
RMS spot size, MTF, or RMS wavefront error. To tolerance an optical system with other performance metrics, such as
ensquared energy, often requires using different techniques. A common method used is Monte Carlo tolerancing. Monte
Carlo tolerancing has advantages and disadvantages as compared to using the tolerancing methods built-in to commercial
optics codes. This paper discusses many of these advantages and disadvantages.
Phase estimation in a Shack-Hartmann wavefront sensor is susceptible to several sources of error, including
spot position noise and induced aberrations. This paper presents an analysis of those errors for a specific
instrument as well as an approach to compensation of the induced aberrations. The compensation scheme
has its own sources of error, and this paper investigates the associated tolerances. In addition, experimental
data is presented for a system that meets the tolerances and performs at the required accuracy.
A velocimetry experiment has been designed to measure shock properties for small cylindrical metal targets
(8-mm-diameter by 2-mm thick). A target is accelerated by high explosives, caught, and retrieved for later inspection.
The target is expected to move at a velocity of 0.1 to 3 km/sec. The complete experiment canister is approximately
105 mm in diameter and 380 mm long. Optical velocimetry diagnostics include the Velocity Interferometer System for
Any Reflector (VISAR) and Photon Doppler Velocimetry (PDV). The packaging of the velocity diagnostics is not
allowed to interfere with the catchment or an X-ray imaging diagnostic. A single optical relay, using commercial lenses,
collects Doppler-shifted light for both VISAR and PDV. The use of fiber optics allows measurement of point velocities
on the target surface during accelerations occurring over 15 mm of travel. The VISAR operates at 532 nm and has
separate illumination fibers requiring alignment. The PDV diagnostic operates at 1550 nm, but is aligned and focused at
670 nm. The VISAR and PDV diagnostics are complementary measurements and they image spots in close proximity on
the target surface. Because the optical relay uses commercial glass, the axial positions of the optical fibers for PDV and
VISAR are offset to compensate for chromatic aberrations. The optomechanical design requires careful attention to fiber
management, mechanical assembly and disassembly, positioning of the foam catchment, and X-ray diagnostic field-of-view.
Calibration and alignment data are archived at each stage of the assembly sequence.
Proc. SPIE 6676, Optical alignment techniques for line-imaging velocity interferometry and line-imaging self-emission of targets at the National Ignition Facility (NIF), 667608 (21 September 2007); doi: 10.1117/12.731639
The National Ignition Facility (NIF) requires optical diagnostics for measuring shock velocities in shock physics experiments. The nature of the NIF facility requires the alignment of complex three-dimensional optical systems of very long distances. Access to the alignment mechanisms can be limited, and any alignment system must be operator-friendly. The Velocity Interferometer System for Any Reflector (VISAR) measures shock velocities and shock breakout times of 1- to 5-mm targets at a location remote to the NIF target chamber. A third imaging system measures self-emission of the targets. These three optical systems using the same vacuum chamber port each have a total track of 21 m. All optical lenses are on kinematic mounts or sliding rails, enabling pointing accuracy of the optical axis to be systematically checked. Counter-propagating laser beams (orange and red) align these diagnostics to a listing of tolerances. Floating apertures, placed before and after lens groups, display misalignment by showing the spread of alignment spots created by the orange and red alignment lasers. Optical elements include 1-in. to 15-in. diameter mirrors, lenses with up to 10.5-in. diameters, beam splitters, etalons, dove prisms, filters, and pellicles. Alignment of more than 75 optical elements must be verified before each target shot. Archived images from eight alignment cameras prove proper alignment is achieved before each shot.
The phase space beam analyzer is a measurement instrument that is applied in laser technology to perform analyses of
the spatial and angular distribution of rays. We are interested in this instrument as a means to characterize non-coherent
light sources. In this context, a closer look at the tolerances of this optical instrument was considered useful.
Having a so-called quadrupole lens as a key element, the phase space beam analyzer is a device that features anamorphic
optical properties. To describe these anamorphic properties, recurrence was made to a description by extended ray-transfer
matrices. This formalism allows for an analysis of the alignment tolerances of the phase space beam analyzer
and facilitates a study of the sensitivities of the instrument. The analysis is complemented using numerical ray tracing.
For all of the interferometers, alignment has played a key role in manufacturing them. Alignment goals are reproducible
results across systems, easy to use and understand, altering overall mechanical design as little as possible, using the
loosest tolerances required to achieve results. This paper describes four typical interferometers and their alignments.
They are 1.06um interferometer, 24" large aperture phase shifting interferometer, Ritchey-Common testing and
microscope interferometer as well.
Computer generated holograms (CGHs) have been successfully used for wavefront correction for measuring aspheric surfaces. Features on the CGHs have assisted the alignment of the optical test equipment. CGHs can also be used to provide alignment references for other complex optical systems. This paper discusses the types of CGHs that can be used for optical alignment and gives some examples.
We developed a distortion measurement technique that works in snapshot mode. Distortion information across the full field of view can be captured in a single short exposure. To do this, a Ronchi ruling is placed in the object and image planes of the system under test. The undistorted ruling in the image plane interferes with the distorted image of the ruling, producing a Moire fringe pattern that can be analyzed in several ways. Phase shifting can be carried out by shifting the Ronchi ruling in object space. The technique is insensitive to vibration and turbulence. Measurements were routinely made with P-V noise levels of 1 μm on measured chief ray locations in 20 mm image planes (0.01%). Repeated measurements showed disagreements on the 6 μm level across a 20 mm image plane (0.03% repeatability).
Laser trackers have been developed that project laser beams and use optical systems to provide three dimensional coordinate measurements. The laser trackers incorporate a servo system to steer a laser beam so that it tracks a retro-reflector, such as a corner cube. The line of sight gimbal angles and the radial distance to the retroreflector are used to determine the coordinates of the retroreflector relative to the tracker. In this paper, we explore the use of the laser tracker to define the metrology for aligning optical systems, including the use of mirrors and windows. We discuss how to optimize the geometry to take advantage of the tracker's most accurate measurements. We show how to use the tracker for measuring angles as well as points.
A variety of tools, such as alignment telescopes and interferometers, are used in the alignment of optical systems.
Alignment telescopes quantify angles, and connect an optical axis to a mechanical axis, but they are not particularly
helpful for quantifying errors in a wavefront. Interferometers, which have exquisite sensitivity and accuracy for
wavefront measurement, are often used for the final qualification of an optical system. However, an interferometer is
not the most convenient tool for alignment. An alternative tool for alignment is the point source microscope (PSM),
which is an example of an autostigmatic microscope. The PSM is a flexible, convenient tool, but like an alignment
telescope, it does not quantify the wavefront. On the other hand, the PSM does provide real-time feedback to an
operator in a compact tool. In order to complete an alignment process it is necessary to quantify the wavefront quality,
and it is desirable to use only a single tool. Methods for quantifying wavefront quality with an autostigmatic
microscope, a tool primarily used for alignment, are described.
The Solar TErrestrial RElations Observatory (STEREO), the third mission in NASA's Solar Terrestrial Probes program,
was launched in 2006 on a two year mission to study solar phenomena. STEREO consists of two nearly identical
satellites, each carrying an Extreme Ultraviolet Imager (EUVI) telescope as part of the Sun Earth Connection Coronal
and Heliospheric Investigation instrument suite. EUVI is a normal incidence, 98mm diameter, Ritchey-Chrétien
telescope designed to obtain wide field of view images of the Sun at short wavelengths (17.1-30.4nm) using a CCD
detector. The telescope entrance aperture is divided into four quadrants by a mask near the secondary mirror spider
veins. A mechanism that rotates another mask allows only one of these sub-apertures to accept light over an exposure.
The EUVI contains no focus mechanism. Mechanical models predict a difference in telescope focus between ambient
integration conditions and on-orbit operation. We describe an independent check of the ambient, ultraviolet, absolute
focus setting of the EUVI telescopes after they were integrated with their respective spacecraft. A scanning Hartmann-like
test design resulted from constraints imposed by the EUVI aperture select mechanism. This inexpensive test was
simultaneously coordinated with other integration and test activities in a high-vibration, clean room environment. The
total focus test error was required to be better than ±0.05mm. We cover the alignment and test procedure, sources of
statistical and systematic error, data reduction and analysis, and results using various algorithms for determining focus.
The results are consistent with other tests of instrument focus alignment and indicate that the EUVI telescopes meet the
ambient focus offset requirements. STEREO and the EUVI telescopes are functioning well on-orbit.
When the optical elements of a system are not collinear, there are advantages to aligning all elements simultaneously.
This paper presents the steps taken to prepare for system alignment and the alignment plan for such a system. A
tolerance analysis of the system defines the compensators necessary for system alignment and allows an estimate of the
expected magnitude of initial aberrations present in the system. Polarization and pupil aberrations are characterized in
order to further understand expected system aberrations before alignment. A two step alignment plan is outlined. First,
a CCD array placed at the focal plane indicates spot size and shape as elements are aligned. Once spot size is
minimized, the CCD array is replaced by a ball bearing for retroreflection. Useful interferograms can be obtained with
which remaining aberrations can be minimized. This technique is presented as the alignment plan for an off-axis
telescope system consisting of one spherical and two ellipsoidal mirrors.
MIRI ('Mid Infrared Instrument') is the combined imager and integral field spectrometer for the 5-29 micron wavelength
range under development for the JWST. The Spectrometer Main Optics (SMO) system has been designed on the basis of
a 'no adjustments' philosophy. This means that the optical alignment precision depends strongly on the design, tolerance
analysis and detailed knowledge of the manufacturing process. Because in principle no corrections are possible after
assembly, continuous tracking of the alignment performance during the design and manufacturing phases is important.
This is done by controlling the "alignment budget" which allows a detailed comparison of the required and achieved
alignment from component to system level. This paper will describe the development of the SMO alignment budget, and
how it is used to bring the alignment performance under control. In addition, we will discuss the results of the actual
alignment measurements on the SMO hardware and the feedback of these results into the alignment budget.
Design details of a cardioid dark field condenser are shown ranging from the theoretical performance of a cardioid to the
best-fit spherical surface. The manufacturing tolerances, fabrication techniques and debug methods are discussed for
this condenser. The primary tolerances to be achieved are center thickness of the cardioid element and maintenance of
its center of curvature relative to the focal plane.
A high precision Co-ordinate Measuring Machine (CMM) is an ideal instrument for aligning mid to large (400 to
600 mm) diameter multiple element lens assemblies. The CMM has many advantages over simpler dial gauge and rotary
table setups. For example, these traditional methods do not necessarily make it easy to separate the out-of-roundness of a
lens or its mounting cell, from a misalignment of the lens and cell. With a CMM, the 'as made' geometry of both the
lenses and their mounting cells can be determined before the mounting and alignment process begins. By considering the
actual shape of the lenses and cells, adjustments can be made during the alignment process to ensure that the complete
assembly meets the designer's tolerances. This paper discusses CMM alignment techniques used and experience gained
while assembling large lens corrector assemblies (for example, the three element Prime Focus Unit for FMOS, the
Subaru Fibre Multi-Object Spectrograph) destined for installation in astronomical telescopes.
In this paper, error analysis and alignment for the optical head of Near Field Recording (NFR) system are presented.
Using optical systems analysis tool - CODEV, the NFR system are designed. After design, we fabricate the NFR system
and test the reading & writing performance of the NFR system. The test results show that the reading & writing
performance is not good enough. In order to find the cause of the performance drop in the NFR system, assembly
tolerances of the optical head of NFR system are simulated. The simulation results show that the tolerance in the optical
head of the NFR system is very tight. So in order to align the optical head within the tolerance limit, we design and
fabricate an alignment system which can detect the RMS wavefront aberration and align the optical head. Before the
experiment, we model the interferometer (by CODEV) and analyze the interference pattern trend. The interference
patterns will be compared with the experiment results. The system can control the position of optical head of the NFR
system using the pico-motor actuators and the capacitance type gap sensors. Using the system, we can align the objective
lens and the solid immersion lens in 5-axis. Finally, we verify the alignment performance of the optical head using the
alignment system. We can align the optical head within tolerance limit using the proposed system.