This PDF file contains the front matter associated with SPIE Proceedings Volume 11488, including the Title Page, Copyright information and Table of Contents.

"Effort was exerted by many people to make the thirteenth Optical System Alignment, Tolerancing, and Verification conference an online success. Thank you to everyone who participated and worked on the conference in 2020. We had an excellent variety of papers across the topics of alignment, tolerancing, and verification. This presentation gives a summary of the conference and conference plans for 2021."

We present an approach to upgrading the beam transport system at the Navy Precision Optical Interferometer. These upgrades together will provide consistent beam transport, improve fringe contrast by preserving beam wavefront, reduce tracking errors by increasing the frequency response of the tracker, and automatically realign the entire transport train after thermal drift over the course of nightly observations. The beam transport system passively redirects stellar light from the telescope output to the fast delay line through a train of flat mirrors. This multi-mirror transport train reduces wavefront preservation due to stack-up of surface flatness errors. We demonstrated previously by using a contour-conformable mirror instead of one of the flats in the train that a 63% improvement in wavefront flatness is achievable. Also, the 25 Hz tracker is replaced by a 100 Hz tracker to further stabilize the trajectory during observations. Finally, we include an auto-aligner to systematically realign the entire beam transport system from thermal drifts. This is necessary for long baseline interferometry with short drift time constants. The beam transport system is common to all front ends (telescopes and siderostats), beam delay, and back-ends (beam combiners and detectors). These three upgrades expand the utility of the NPOI from a relatively short 97 m baseline interferometer to its full reconfigurable 437 m baselines and allow consistent beam transport with various potential experimental telescope front ends and beam combiner back-ends. In this paper, we describe our three-pronged upgrade approach, experimental method and results, and recommendations.

For the first time in the history of ground-based y-ray astronomy, the on-axis performance of the dual mirror, aspheric, aplanatic Schwarzschild-Couder optical system has been demonstrated in a 9:7-m aperture imaging atmospheric Cherenkov telescope. The novel design of the prototype Schwarzschild-Couder Telescope (pSCT) is motivated by the need of the next-generation Cherenkov Telescope Array (CTA) observatory to have the ability to perform wide (≥8°) field-of-view observations simultaneously with superior imaging of atmospheric cascades (resolution of 0:067 per pixel or better). The pSCT design, if implemented in the CTA installation, has the potential to improve significantly both the x-ray angular resolution and the off-axis sensitivity of the observatory, reaching nearly the theoretical limit of the technique and thereby making a major impact on the CTA observatory sky survey programs, follow-up observations of multi-messenger transients with poorly known initial localization, as well as on the spatially resolved spectroscopic studies of extended x-ray sources. This contribution reports on the initial alignment procedures and point-spread-function results for the challenging segmented aspheric primary and secondary mirrors of the pSCT.

High-quality imaging is typically dependent upon well-focused optical systems. We present a method that linearizes defocus to provide a clear zero-crossing along the optical axis for structured light illumination (SLI) systems. Here, sinusoidal fringes are projected onto a quad target, a diffuse target with different heights along the optical axis in separate quadrants. Shifting the focus alters the fringe contrasts on the quad target. Best focus is achieved when the contrast between the different heights is balanced. The method was tested using a commercial SLI system and compared to a published phase-shifted reconstruction technique. The non-linear defocus behavior was efficiently linearized using the quad target method as evidenced by linear regressions. Finally, focal position estimates agreed well with the phaseshifted technique, thereby demonstrating viability of the method.

A practical instrumentation configuration for measuring focal length of cell-phone camera lenses is presented that uses a custom autocollimator, a grating, an autostigmatic microscope, and a precision stage. Uncertainty in LED wavelength is reduced by using a white LED and a set of narrow-band filters. The autocollimator is designed to allow for rapid focus adjustment at each test wavelength. Examples of the measurement technique and an error analysis are provided.

With the recent addition of Moore's high-yield feature in Zemax, a convenient path to optimiza- tion for as-built performance while reducing computation time has been introduced. In order to analyze the cost and outcome of optimization with the new feature and other approaches, we consider a side-by-side comparison of the conventional approach, high-yield approach, and other alternatives. The benchmark design under consideration is a basic Double Gauss lens due to the extensive studies of its variants since its conception. A total of eight approaches are considered, and the resulting designs and their tolerance sensitivities are presented in order to provide recommendation of a favorable approach.

Optical systems are often athermalized over large temperature ranges through the proper choice of glasses and mounting materials. However, variations in the coefficients of thermal expansion (CTE) and thermo-optical coefficients that govern thermal behavior are seldom included in the tolerance analysis. Manufacturers rarely provide these material tolerances and we can only account for their effects through custom macros in lens design software. We demonstrate that a first-order sensitivity analysis on the change in focus position at each environmental condition accurately predicts the degradation of the system performance. We verified this correlation by creating a custom catalog of identical glasses with perturbed thermal parameters and evaluating the RMS wavefront error for each material substitution.

We describe an eigenmode analysis technique that can be used to determine how an optical system will react to tolerances. The input stimuli are the tolerances of the system, and the resulting eigenmodes are the aberration patterns that will be “driven” by them. The eigenmodes are orthogonal and include both pupil and field dependencies: field-uniform coma, field-uniform lateral color, and field-linear, field-asymmetric astigmatism are examples. The eigenvalues provide a means of rank-ordering the eigenmodes according to importance when considering a set of alignment compensators that might be included in the system to mitigate the effect of tolerances.

We discuss detailed tolerancing methods developed for imaging spectrometers at NASA Jet Propulsion Laboratory, California Institute of Technology using the Earth Surface Mineral Dust Source Investigation (EMIT) imaging spectrometer as an illustrative example. We tolerance five metrics simultaneously: along-track response function, crosstrack response function, spectral response function, spectral centroid uniformity, and spatial centroid uniformity. A method to calculate tolerancing sensitivities for each metric directly, a method to statistically combine Monte Carlo files from multiple tolerancing runs, and example summary error budgets that communicate the key and driving tolerances for each metric are discussed. These methods facilitate rapid and semi-automated assessment of the predicted performance of imaging spectrometer systems from design through to assembly and launch life cycle, using metrics that are directly relevant to the extraction of accurate spectroscopic data from these instruments.

We study the propagation of wavefronts produced through cemented doublet lenses, considering a plane wavefront propagating parallel to the optical axis. We provide formulas for the zero-distance phase front by using Huygens's principle, also we provide formulae to represent the shape of refracted wavefronts propagated arbitrary distances along the optical axis, which are function of all parameters involved in the process of refraction. We present examples of doublet lenses showing the evolution of the wavefronts arbitrary distances, assuming different wavelengths for the refractive indices of the lenses, for this purpose we compare the dispersion effects produced through this particular kind of lenses.

Prototype zoom lenses should be designed with flexibility. One never knows what the future use of a prototype as-build lens will be. In a prior design of a large-image-format zoom lens used for proton radiography, extra back focal distance was constrained in the design to allow for future insertion of extra lenses. These added lenses can change the magnification to a different camera system, having a smaller image size. Three single commercial lens elements were mounted into a commercial variable-length housing barrel that was attached to the back of the zoom lens using a 3Dprinted flange. This new design has been adapted to support neutron radiography; the new configuration collects light from a thick, blue-light-emitting scintillator. After the initial request was made, it took us only three weeks to design, assemble, and conduct imaging tests. The scintillator’s light travels 24 inches before entering into the zoom lens. A large pellicle is inserted into the optical path to keep the zoom lens and camera out of the neutron flux. Because of reduced resolution from the volume scintillator, a five-axis self-leveling alignment laser was sufficient to adjust the tilting of the scintillator, pellicle, zoom lens, and camera. The design process for picking suitable COTS lens elements will be discussed.

Spherical aberration has long been considered the bane of optical design. It is especially bothersome in optically fast as well as wide field designs. Aligning axial and off-axis aspheric mirrors have also been considered difficult due to the general issues of properly positioning these elements during the alignment process. As part of this difficulty, establishing the optical axis of the parent aspheres has been a problem, and spherical aberration can offer the solution as an alignment tool. The information in this paper has been taught for over 20 years in the SPIE Short Course “Introduction to Optical Alignment Techniques.” To those students who have taken this course, the material is not new, but to the general optics community, it may offer a new perspective.

The LRCTF (Laser Ranging Characterization and Test Facility) is a unique facility built at NASA GSFC to provide thermal-optical testing of the next generation GPS LRA (Global Positioning Satellite’s Laser Retroreflector Array) laser ranging target. The 400mm diameter target is an array consisting of 48 total internal reflection retroreflectors and has an optical cross section requirement of 100 MSM (million square meters). To verify that the array meets this requirement during on-orbit conditions, the LRCTF is equipped with a 400mm test beam, a data product output consisting of full aperture FFDPs (Far Field Diffraction Patterns) and a thermal chamber. The FFDPs are used to calculate the OCS. This paper will describe the facility design, alignment approach, and verification process.

Bessel beams have found use in the alignment of transmissive optics for some time. They are also used for the alignment of reflecting optics when used in the imaging mode, that is, when the wavefront is near spherical. However, there are cases where it would be useful to use the Bessel beam for alignment of far-off axis aspheres to order to get the asphere aligned close enough to its final position that light will go through the system in the imaging mode. In another mode, the Bessel beam is used to determine the normal to a free form surface.

An important question in the development of the Roman Space Telescope (RST) is how to optically test it at the highest levels of assembly, after the instruments have been integrated with the telescope. Our current strategy is double-pass testing using image-based wavefront sensing (phase retrieval). In this paper, we consider alternative strategies based on Hartmann testing, using either a pupil-plane mask or a mirror array. We developed first-order design considerations for the implementation of such Hartmann tests in the context of RST and designed two specific Hartmann tests to evaluate in further simulations. One of the major suggested benefits of Hartmann testing is insensitivity to vibrations that induce either line-of-sight jitter or dynamic changes in wavefront aberration. In order to understand whether this is true (and under what conditions), we developed a physical optics simulation of our two Hartmann tests under both Gaussian line-of-sight jitter and sinusoidal dynamic secondary mirror motion. We then also developed a data reduction process for fitting these Hartmann test images and estimating system wavefronts.

Double-pass optical testing will play a key role in the alignment and verification of the Roman Space Telescope (RST), NASA’s upcoming flagship astrophysics mission, which was formerly known as the Wide Field Infrared Survey Telescope or (WFIRST). In this test configuration, optical fibers adjacent to the focal plane detector array will send light through the entire optical system in reverse, to be reflected off an auto-collimating flat (ACF) mirror and back through the system a second time (at a different angle) before reaching the detector. The ACF will be tilted through a range of angles to provide samples across the entire field of view, which is exceptionally large for a space telescope and will exhibit measurable field-dependent aberration. Phase retrieval analysis of the resulting point-spread functions will provide wavefront estimates; however, these wavefronts will include aberrations that were accumulated on both passes through the system at their respective field angles. In order to evaluate the alignment and verification of the system, we must predict the performance of the observatory when operating in single-pass. Therefore, we present an algorithm that will separate the aberrations from the two passes to provide a prediction of the telescope’s performance in single-pass. This is done by fitting the data to a polynomial representation of the underlying field aberrations and requiring that the aberrations accumulated on the two passes be consistent with that model.

A common method for aligning a telescope in a laboratory setting is to place an interferometer at the focal plane and a return flat in collimated space. For some long wavelength systems that need to be aligned, or checked in the field, transporting an interferometer and a large flat are not practical. One example is a balloon borne terahertz telescope. In this paper, we present an alignment approach that does not require an interferometer or return flat. Instead of using a traditional approach, we are proposing the use of deflectometry and the sine condition test to determine the state of alignment. Both of these tests can be done with the same equipment which primarily consists of a camera and an LCD larger than the clear aperture of the telescope. Deflectometry is used to measure defocus, spherical, and on axis coma while the sine condition test measures linearly field dependent astigmatism. These are the low order aberrations that will be affected by misalignments, and their magnitudes and orientations can be used to align the system. We explain how this approach is used, show the results of simulations, and predict the expected performance of a telescope aligned with this approach.

A vacuum-compatible manipulator was developed to calibrate the Miniaturized UltraViolet Imaging instrument (MUVI). The pointing resolution of the manipulator was evaluated, along with its ability to neutralize known optical misalignments. Field of View sweep tests were performed to quantify manipulator parameters using optical ground support equipment. Systematic errors were effectively reduced by a factor of 49 and 7 in the horizontal and vertical translation axes, respectively. Furthermore, the pointing resolution was measured to be less than 1 arcmin, which satisfied the instrument’s science calibration requirement.

Today, multiple technological instruments facilitate the work of the researcher. These instruments are provided with some features given by the manufacturer. However, it is important to verify these features to be sure that the instrument works properly and does not have any influence on the results of an experiment. In this study, we consider the electrically focus-tunable lenses (EFTL), whose main feature is the fast and efficient control of its focal length. This feature has allowed its use in several areas of optics like visual optics, and nonlinear optics, where precision is an important requirement. In this context, it is important to guarantee that the programmed focal length on the EFTL matches with the actual focal length driven on the lens. Recently, it was shown that the EFTL presents a hysteresis effect, which, according to the datasheet, should not exist. In this work, we develop a complete optical calibration of some EFTLs to evaluate the performance of the lenses. Three EFTLs were studied. Two of them had an optical power variation from +8.3 to +20 Diopter (D), while it was from -10 to +10 D for the other one. It was confirmed the existence of hysteresis for all these EFTLs. Additionally, we present an experiment that intends to answer the question about whether all the lenses of the same reference will have the same hysteresis curves. Finally, we study the behavior of several aberration terms as a function of the induced current, to explore the existence of hysteresis in other aberrations terms different from the defocus.

An optical system is proposed for wavelength measurement and detection using phase vortices produced by an integrating glass disc. This optical system is based on a modified digital holographic configuration used previously for measurement in Particle Image Velocimetry (PIV) but adapted here for the detection of phase vortices generated by an integrating glass disc. Phase vortices are detected from speckle patterns that are produced using a tunable light with a wavelength of 632 ± 2 nm emitted by a Littrow monolithic tunable external cavity laser, and after multiple reflections in the integrating disc combined with a reference beam and a speckle interferogram is obtained that recorded by a CCD camera. The Fourier transform method is used for speckle phase generated in the proposed optical configuration and analyzed with a vortex detection method that produces a singularities pattern for each wavelength.