This PDF file contains the front matter associated with SPIE Proceedings Volume 11816, including the Title Page, Copyright information, and Table of Contents

High-quality imaging is typically dependent upon well-focused optical systems; however, precise focusing can be difficult due to the non-linearity of defocus. This paper presents further development of the quad target method (QTM), an alignment technique to linearize defocus for structured light illumination (SLI) systems, by creating a method to simulate the alignment sensitivity. QTM’s sensitivity is the slope of the regression that linearizes defocus and is dependent upon the step height of the quad target and the frequency of the projected fringes. The presented simulation method utilizes the native optical design to faithfully model the residual aberrations and is able to predict the best focus location as a well as the linearized slope. The predicted slope and best focus were compared to experiment using a commercially-available SLI system. For a step height of 500 μm and projected fringe frequency of 6.8 cy/mm, the simulation method predicted the slope to within 5.4% and best focus to 17.7 μm of the measured values.

Bessel beams are useful for alignment because they create a small diameter, bright, straight line image in space perpendicular to the Axicon, or Axicon grating, producing the beam that is an exact analog of a single ray in a ray tracing program. Here we limit our discussion to Bessel beams produced by plane gratings whose pattern is evenly spaced concentric circles that are illuminated by a point source of light on the grating axis. The gratings produce a more nearly ideal Bessel beam than a lens type Axicon, and the plane grating serves as a plane mirror as well in an alignment setup so the combination define four degrees of freedom in space rather than the usual two. Most discussions of Bessel beams assume illumination with collimated light. We have found it advantageous to use a point source for illumination because it is easy and less expensive to use a single mode fiber as a source than a precision collimating lens the diameter of the Axicon. Besides, collimated illumination produces a Bessel beam of finite length in transmission while in theory a beam of infinite length is created using a point source. With these assumptions about how the beams are produced and details about the grating diameter and line spacing it is easy to calculate the useful length of the Bessel beam in reflection from the grating, the usual matter of concern when using the grating for alignment purposes in a double pass test setup. Other practical matters are also discussed such as lens centering with a test apparatus with no moving parts.

Future large space telescope missions demand extreme stability to enable high contrast coronagraphy for exoplanet observation. The wavefront control systems needed to achieve and maintain the required wavefront quality of the imaging system requires high-performance metrology sensors capable of picometer class sensitivity over long duration exposures, as well as for ground-based verification of build performance. For nearly two decades, Lockheed Martin has invested in developing laser metrology gauge technologies implemented in Photonic Integrated Circuits (PICs). We describe a high precision displacement metrology system currently under development and in test which has a path to flight for these future systems. Recent implementations have demonstrated picometer-class sensitivity at high (< 1 Hz) frequencies using largely commercial-off-the-shelf hardware. The current work aims to improve performance at longer timescales.

Interrogating ejecta particles launched from target materials that are undergoing dynamic shock can be done with both xray imaging and visible shadowgraph imaging. Our dynamic testing must be done inside a containment vessel with limited access ports available. We designed an imaging system to relay both types of imaging systems through a single port using the same optical relay and then splitting the images onto three separate high-speed imaging cameras outside the containment vessel. X-ray imaging provides ejecta density measurements. Shadowgraph imaging that is done at two wavelengths (blue and red) constrains ejecta particle size distributions and provides areal density measurements of the ejecta cloud. The ejecta particles are positioned 225 mm before the x-ray scintillators; this arrangement permits a folded mirror system to allow the shadowgraph data to bypass the x-ray scintillators. This configuration results in spatial separations between the intermediate image planes of the x-ray and shadowgraph images along the optical axis. At the position of the x-ray intermediate image plane, mirrors are positioned such that the shadowgraph images are kicked out and their images are sent on to different cameras. Positioning of the large doublet relay lenses keeps shrapnel from impacting the vessel containment windows.

Historically polarization maintaining fiber requires manual alignment of five degrees of freedom to optimize coupling with the waveguide of a lithium niobate sliver used to fabricate an optical modulator. This manual process for a Y-branch modulator needs to be completed four times on the sliver with a temporary, input and two output optical fiber pigtails being installed. In this abstract we will introduce combining these four pigtail operations into single station and automating the alignment process through the novel use of several virtual pivot points surrounding two ultra-precision 6-axis actuators. Customized fixturing mounted to different areas of each actuator allows for a single station to accomplish all four unique pigtail attachment operations without having to swap out and realign tooling. The optical fiber pigtail assemblies are gripped by the fixturing on the actuators, while the lithium niobate sliver is mounted to one of two separate stationary locations surrounding the actuators, depending upon which pigtail alignment operation is being performed. Automated control software then optimizes the fiber-to-modulator waveguide alignment prior to and during the bonding of both elements. The result is a highly repeatable and efficient optical fiber pigtail attachment process with substantial cost savings.

Optical systems such as X-ray telescopes or micro-optical systems can require alignment of optical components with nanometer-level tolerances, and often with stringent volume and mass requirements. We propose fabricating, bonding, and subsequently adjusting length of glass spacers using ultrafast lasers. Ultrafast laser processing has been industrialized over the last decade for micron-accuracy glass cutting with complex shapes, and for glass-to-glass and glass-to-metal welding. In this paper, we will show experimental results demonstrating the ability to generate stable strain in Corning® Eagle XG® glass samples, which causes permanent nanometer-scale length changes. We demonstrate a total strain of ~10-3, or microns of displacement per millimeter length of laser-modified glass. We also measure stability in laser-modified samples and find that the length changes are nanometer-stable. We also show how this process may be applied for alignment of X-ray mirrors by combining industrialized ultrafast laser processes for glass cutting and glass-to-glass welding with strain generation and control. This powerful and flexible process may enable compact, lightweight set-and-forget alignment of optical systems with nanometer tolerances.

An off-axis, three-mirror anastigmat was optically aligned for minimum wavefront error using three different analysis methods to improve alignment efficiency. The three methods involved CODE V Automatic Design (AUT), CODE V Alignment Optimization (ALI), as well as a Zernike Sensitivity Analysis (SENS). Not all methods converged on the same solution during alignment, but all tools were used in unison to optimize the optical alignment process. During initial optical alignment, the AUT tool better estimated the proper magnitude of the required alignment. As alignment progressively became finer, the ALI and SENS tools both produced superior, more in-family alignment solutions. Conclusively, depending on the coarseness of the optical alignment required, all alignment strategies have their merits, but most importantly each tool provides a check against other alignment solutions. Therefore, all tools aid in directing the optical alignment towards a global minimum.

The Off-plane Grating Rocket Experiment is a soft X-ray grating spectrometer payload to be launched on a suborbital rocket. The spectrometer will use three technologies – monocrystalline silicon X-ray optics (NASA Goddard Space Flight Center), X-ray reflection gratings (The Pennsylvania State University), and electron-multiplying CCDs (XCAM Ltd., The Open University) – to achieve the highest performance on-sky soft X-ray spectrum to date when launched. To realize this performance, not only must each of the three individual spectrometer components perform at their required level, but these components also must be aligned to one another to the required tolerances and integrated into the payload. In this manuscript, we report on the alignment and integration plan for each component within the spectrometer.

Freeform optics have had a significant impact in airborne systems and other applications and are a key enabler for spaceborne systems. Their complex shapes allow the production of optical systems with reduced physical size and weight, together with improved performance. The sophisticated fabrication technologies that have enabled freeform optics also give rise to manufacturing challenges not encountered in the production of traditional, rotationally symmetric spherical and aspheric optics. Since manufacturing complexity has both a cost and lead time impact, it’s useful to have some means to predict how readily a specific design can be fabricated. This paper shows how an analysis of low- and mid-spatial frequency errors on various types of aspheric components leads to the use of rate of change of surface curvature as an easily derived and useful predictive metric to manufacturing complexity.

We previously demonstrated automated alignment of a multi-element reflective system using existing internal imaging components and model-based optimal estimation in simulation. Using multiple versions of Kalman filtering, we were able to consistently bring the linear misalignments from around 1 mm to < 5 μm and the angular misalignments from around 500 arcsec to < 6 arcsec. This paper presents our preliminary experimental results and further analysis on the system. Specifically, we conduct information-based observability analysis to investigate the multi-state coupling effect and to evaluate our algorithm design, which provides insight into future improvements. We also discuss the current error sources in the experiments.

The discipline of optomechanical engineering has few dedicated courses and no complete programs at universities in the US. Yet, optomechanical engineering is a discipline that is vitally important to many sectors, including defense, aerospace, semiconductor, military, medical, and more. To truly turn optomechanical engineering into a complete discipline, educational programs must be established where the spine of the program is optomechanical engineering, rather than it simply existing as optional elective courses. This paper details the possible framework for such a program based on lessons learned from educating students at both the University of Rochester and the University of Arizona, which contain the two most prominent optics education programs in the US.

Determining preload for mechanical fastener hardware such as screws and bolts is critical to a successful aerospace mission. Preload helps to ensure that fatigue failure during operation is minimized, prevents gapping under applied dynamic loading while minimizing change in preload, and can prevent friction slip under high lateral loads. Many codes have been developed to approximate hardware torque to preload relationship dependent on friction, and high uncertainty factors are indicated (up to 35%) to bound analyses. More precise measurement of preload requires costly technique using strain gage or micro precision instrumentation. An approximate but low-cost method of determining preload for a given application is presented to prevent underloading of components, using standard hardware analytical techniques and breadboard testing. Results are shown accurate to better than the uncertainties, which can assist in determining proper torque requirement. Included are both lubricated and non-lubricated hardware, and effects of washers on preload.

Free-space laser communication systems are increasingly implemented on state of the art satellites for their high-speed connectivity. This work outlines a demonstration of the Modular, Agile, Scalable Optical Terminal (MAScOT) we have developed to support Low-Earth Orbit (LEO) to deep-space communication links. In LEO, the MAScOT will be implemented on the International Space Station to support the Integrated Laser Communications Relay Demonstration (LCRD) LEO User Modem and Amplifier Terminal (ILLUMA-T) program. ILLUMA-T's overarching objective is to demonstrate high bandwidth data transfer between LEO and a ground station via a geosynchronous (GEO) relay satellite. Outside of LEO, the MAScOT will be implemented on the Artemis-II mission to demonstrate high data rate optical communications to and from the moon as part of the Optical to Orion (O2O) program. Both missions leverage the same modular architecture despite varying structural, thermal, and optical requirements. To achieve sufficient performance, the terminal relies on a nested tracking loop to realize sub-arcsecond pointing across a ±120 ° elevation and ±175° azimuth field of regard.

Our work in the Laboratory of Space Systems and Optomechanics (LASSO) at Texas A&M University involves using optomechanical resonators coupled with compact, high-precision interferometers to create novel inertial sensors. These resonators are etched from monolithic fused silica, which is known to have very low internal losses, allowing for high mechanical quality factors and low thermal acceleration noise in the test mass. Previous measurements at mTorr pressures have demonstrated Q’s of 1.91 x 10⁵, corresponding to estimated thermal acceleration noise floor on the order of 10-10 m s^{- 2}/√Hz for frequencies above 30 mHz. In this pressure regime, gas damping is still the dominant loss mechanism. At sufficiently low pressures such that gas damping is negligible, we anticipate mechanical quality factors of the order of 106 and thermal acceleration noise at levels of 10^-11 m s^-2/√Hz in the sub-Hz regime. As expected, previous measurements have shown significant ambient vibrations that limit our ability to observe the noise floor of the resonator. Hence, we have developed a dedicated vibration isolation platform to mitigate external disturbances, which consists of a pendulum with a magnetic anti-spring to lower the resonant frequency. Sensors constructed with these resonators would be lightweight and cost-effective, making them promising candidates for field applications in geophysics, navigation, and site exploration.

Additive manufactured micro-optical systems and elements via two-photon polymerization already show a wide range of applications. To extend that range, mechanical features such as autofocus, zoom or tilting could be realized by implementing actuatable components in the printed opto-mechanical design. We demonstrate a magnetic actuation principle, where ferromagnetic fluids are injected into predefined microcavities. In this way, optical parts can be actuated through external magnetic fields in continuous manner and restored to their original position by retracting mechanical components embedded in the design. We demonstrate different kinds of motions regarding use cases in endoscopic applications.

Freeform surfaces offer many advantages in the design of optical systems. To perform STOP analyses[1] of systems containing freeform surfaces, the nominal surface geometry must be accurately represented. Forbes polynomials[2] (sometimes called Q2D polynomials) are often used to represent freeform surfaces in optical design codes. This paper discusses the use of Q2D polynomial surfaces in STOP analysis. Topics include comparison to standard Zernike polynomials and passing finite element results to optics analysis software.

Lightweight, athermalized mirror design remains a critical technology area for space-based applications, often requiring specialized optical evaluations not available in most commercial mechanical simulation software. The highest performing stiffening patterns require powerful CAD tools to parametrically model while maintaining continuity with complex solids, but integrating this engine with optomechanical analysis software requires extensive development from the user side. Lincoln Laboratory has created an API to accomplish exactly this, including full automation of the entire CAD to FEA to optical performance workflow. We have demonstrated this capability on a compact, off-axis beam expander with steep surface curvature subject to various gravity orientations and thermal loads, while studying the effect lightweight stiffening patterns on focus-subtracted wavefront error.

Determination of the optimum mount zone to minimize gravitational deformation of mirrors, when gravity is aligned with the optical axis vertical, is well-documented. Less has been written about such optimum zones when such mirrors, particularly lightweight cored optics, are aligned with the gravity axis normal to the horizontal optical axis. An equation is herein presented to determine the optimum axial mount zone to minimize wavefront error in this environment, for powered optics (finite radius of curvature). Generally, for most optical systems, wavefront error is lower in this configuration than in the vertical axis orientation, important for ground test of space-based optics. When mounted at three near-kinematic points, determined is an equation to find ideal axial mount location at any radial mount zone to minimize error and an equation to predict gravitational deformation that bounds all mount zones to conservatively estimate performance error. Optimum zones are found to lie near, but not coincident to, the mirror centroid and/or neutral surface. These analyses allow the engineer to quickly determine first order errors considering design envelope restrictions, prior to more detailed finite element analyses.

Transient operating temperatures often allow a lens cell to expand before the lens itself, potentially leading to stresses well in excess of the lens tensile strength. The transients thus affect the calculation of the athermal bond-line thickness, estimates of which have historically been based on thermal equilibrium conditions. In this paper, we present both analytical expressions and finite-element modeling results for thermal-transient bond-line design. Our results show that a cell with a large CTE and a bond thickness based on thermal transients is the best strategy for reducing the tensile stress on the bonded lens over a range of operating temperatures.

In wide-field telescopes, relatively small misalignments in the optical system can cause large aberrations. The nominal system is normally designed to show a good optical performance over the whole field of view but, in presence of misalignments, the symmetry is broken and the aberrations increase towards the edge of the field. No new aberrations arise, but the known aberrations behave differently and originate multiple nodes, according to the Nodal Aberration Theory. The effects, in terms of image quality degradation, can be especially deleterious for wide-field imagers. This issue can be studied in detail by the ray-tracing programs that are normally adopted for the optical design. Nevertheless, these codes are not optimal for applications where a high execution speed is needed. Here, an application of PSF reconstruction for a wide-field telescope by using an integrated modeling approach is presented. Ray-tracing data are adopted as input to build a fully analytical model. The example of the VST telescope (1x1 deg field of view) is discussed as a case study.