This PDF file contains the front matter associated with SPIE Proceedings Volume 13134, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Confocal probes, which consists of a point light source and a point detector, have been widely used in the manufacturing industry for a surface profile measurement of a measurement target object. In recent years, a mode-locked laser, which has advantages; high-stable optical frequency and wide-range optical frequency, and high-stable intensity, has been employed as a light source of the confocal probes, enabling to non-scanning and precise height measurement. However, a non-smoothness of the optical spectrum of the mode-locked laser affects a confocal response curve, which is utilized for the target position measurement, and leads to loss of the measurement accuracy. Therefore, a dual-detection chromatic confocal probe has been proposed and researched to reduce the effects of the non-smoothness optical spectra. In this paper, a review about the dual-detection chromatic confocal probe is summarized.

Optical aspherical surfaces have become more widely used as they offer advantages such as improved image quality, compact design, increased light gathering, and reduced distortion. However, measuring aspherical surfaces presents challenges due to their non-spherical shapes. The primary difficulties include the complexity of surface geometries and the need for specialized metrology equipment. These challenges require advanced measurement techniques to ensure accurate characterization and quality control of aspherical surfaces in various applications. This paper introduces an innovative, AI-driven solution for the measurement of aspherical surfaces within the image space, offering a flexible optical metrology tool for measuring aspherical surfaces. This approach is characterized by its ability to deliver rapid and cost-effective integration without the need for custom, complex optics.

In optical metrology, the growing demand for accurate measurement technologies is driven by the increasing applications of three-dimensional (3D) microscopy and imaging. The advancement of these technologies relies on the modelling of the measurement process, where an initial step involves characterising the interaction between electromagnetic fields and surfaces, to determine the scattered electromagnetic field, and the subsequent propagation of the scattered light through the instrument. Virtual instruments (VIs) can play a critical role by replicating optical instruments through surface scattering models, 3D imaging theory and error-generation models. The development of VIs contributes to a better understanding of instrument characteristics, optimising configurations and evaluating uncertainties. VIs can be customised to simulate various optical setups, providing researchers with flexibility to explore optimal measurement settings. Furthermore, the integration of sophisticated computational tools and machine learning to VIs can enable real-time, in-depth and optimal analysis of optical instrument modelling. Coherence scanning interferometry (CSI) is a widely used optical technique for high-accuracy surface topography measurement. A virtual CSI (VCSI) models the CSI measurement process using physics-based models. Approximate scattering models, utilising basic scalar diffraction and linear imaging theories, facilitate CSI modelling that can offer insights into the fundamental sources of measurement error for smooth surfaces. However, with the increasing use of complex freeform manufactured structures in engineering, aerospace and biology, scrutinising complex surface features becomes more critical. As a result, rigorous scattering models, based on solutions of Maxwell’s equations, can be used as tools for addressing more complex light-matter interactions. Capable of calculating light scattered fields from any surface geometry while taking into account different light phenomena, such as polarisation, rigorous models provide high-accuracy solutions. In this study, we compare the simulated fringe pattern and reconstructed profiles obtained by virtual coherence scanning, employing both approximate and rigorous scattering models for sinusoidal and vee-groove samples.

Absolute distance measurement has been widely required not only in various industrial fields such as semiconductors, displays, and heavy industry, but also in fundamental and applied research sites. Among the various optical methods for measuring absolute distances, the most widely used method with high precision is multi-wavelength interferometry. In general, multi-wavelength interferometry uses three or more frequency-stabilized lasers to solve the phase ambiguity problem from a large amount of phase information corresponding to several wavelengths. However, despite the high measurement precision of multi-wavelength interferometers, it is practically not easy to install and maintain several frequency-stabilized lasers in terms of cost and maintenance. In this work, we aim to implement a multi-wavelength interferometer using an electro-optic comb with wide spacing between frequency modes. Because the frequency mode spacing of the electro-optic comb is wide enough to be resolved by commercial spectrometers, each frequency mode can be considered as a single frequency-stabilized laser. Through this concept, several frequency-stabilized lasers for multiwavelength interferometer can be replaced with a single electro-optic comb. Absolute distance measurement was performed using the proposed method, and measurement uncertainty evaluation was also performed to evaluate the proposed method. When the electro-optic comb is stabilized by being locked to an atomic clock being traceable to the time standard, so it is expected that it can be easily used to realize length standards or measure ultra-precise absolute distances in the future.

An electro-optic comb has a wide frequency mode spacing of more than several tens of GHz, making it possible to resolve each comb mode by using commercial spectrometers. The individual frequency modes of the electro-optic comb can be employed as the multiple stabilized lasers required for a multi-wavelength interferometer in absolute distance measurements. For absolute distance measurements, the phase information for each frequency mode, i.e., wavelength, is necessary for determining the absolute distance using the excess fraction method, and this requires a phase shifting process. Typically, the phase shifting is implemented through the sequential translation of a reference mirror by an equal distance. However, since the wavelength values corresponding to every frequency mode are different, even the same amount of shifting of the reference mirror generates different phase change for each wavelength. In such a situation, to accurately measure the phase for each wavelength, a model-based analysis method for phase shifting intensity signals itself was adopted. In the model-based analysis of phase shifting intensity signals, the phase determination uncertainty can vary depending on the number of the phase shifting step. Therefore, in this study, we aim to estimate the phase determination uncertainty according to the number of the phase shifting step through numerical simulations.

An on-axis deflectometry method for measurement of refractive optics is proposed and demonstrated. This system measures wavefront error of a refractive unit under test using a camera, monitor and parabolic mirror all aligned on a single axis. In this way light from the monitor reflects from the parabolic mirror into the aperture of the camera. A null configuration is created when there is no test lens under the test setup. The test lens configuration occurs when a lens is inserted between the mirror and the aperture of the camera. The displacement of image locations of spots displayed on the monitor is analyzed to calculate the wavefront error of the test lens. The system concept is described, the system was built and described, and the procedure was explained along with the reported wavefront error in terms of the first 11 Zernike terms. The test lens position tolerance was evaluated to have +/- 0.13 Diopter accuracy test result.

Traditional surface metrology mainly focuses on measuring distances between the sensor and the workpiece to characterize the surface topography and gain insights into geometric properties of the workpiece. This involves quantifying features like roughness using standardized surface texture parameters of ISO 25178 and ISO 21920. However, these parameters may not always offer a comprehensive understanding of a surface's functional aspects. For certain applications that require a highly sensitive process monitoring, the distribution of the surface gradient can provide complementary information about the functionality of the surface. We present a study to establish a direct correlation between the angular-resolved scattering light distribution and the functional characteristics of surfaces. While the sensor principle is commonly used for process monitoring, the relationship between the angular distribution and the functional characteristics like wear, friction, and lubrication has not been widely examined. As a case study, cylinder liner surfaces representing a diverse range of surface topographies with high functional requirements are examined. Functional surface texture parameters are determined as a benchmark using both tactile and optical surface topography measuring instruments. The results emphasize the importance and opportunities of directly connecting the angular distribution data with functional characteristics.

Precise characterization of deformable mirrors (DMs) is crucial for optimizing wavefront sensing and control systems. This study employs a 4D PhaseCam 6000 interferometer to investigate the temporal behavior of a 97-actuator ALPAO DM across varying levels of aberration. Analysis of root mean square (RMS) differences and changes in the first 37 Zernike polynomials demonstrates a clear correlation between applied aberrations and temporal variability. We observe a consistent pattern: as the applied magnitude of the RMS to the DM increases, so does the disparity between maximum and minimum RMS values across all configurations, with exceptions noted in cases involving coma and scenarios without applied aberrations (DM powered on and DM powered off). Notably, in 11 out of 14 measurements, either oblique astigmatism or vertical astigmatism exhibits the highest variability, often appearing together, underscoring their collective impact on DM performance over time.

Continuous wavefront sensing benefits space observatories in on-orbit optical performance maintenance. To measure the phase of a wavefront, phase retrieval is an attractive technique as it uses multiple point spread function (PSF) images that are acquired by the telescope itself without extra metrology systems nor complicated calibration. The focus diverse phase retrieval utilizes PSFs from predetermined defocused positions to enhance the dynamic range of the algorithm. We describe an updated visible light active optics testbed with the addition of a linear motorized focus stage. The performance of the phase retrieval algorithm in broadband is tested under various cases. While broadband pass filters have advantages in higher signal-to-noise ratio (SNR), the performance of phase retrieval can be restricted due to blurred image caused by diffraction and increased computing cost. We used multiple bandpass filters (10 nm, 88 nm, and 150 nm) and investigated effects of bandwidth on the accuracy and required image acquisition conditions such as SNR, reaching accuracies below 20 nm RMS wavefront error at the widest bandwidth. We also investigated the dynamic range of the phase retrieval algorithm depending on the bandwidth and required amount of defocus to expand dynamic range. Finally, we simulated the continuous wavefront sensing and correction loop with a range of statistically generated representative telescope disturbance time series to test for edge cases.

We are developing a Hybrid Wavefront Sensor which combines the high dynamic range of a Shack-Hartmann wavefront sensor and the high sensitivity of an unmodulated pyramid wavefront sensor. In our prototype, composed primarily of commercially available optics and 3D printed mounts, light is focused at the center of a crossed roof prism to create four identical pupils that each pass through a lenslet array which allows us to simultaneously perform Shack-Hartmann and pyramid wavefront sensing analyses on aberrated wavefronts. By using this hybrid method, an adaptive optics wavefront sensing setup could continually perform wavefront corrections with a deformable mirror (DM) during turbulent events that would saturate an unmodulated pyramid wavefront sensor functioning on its own. To test our prototype, multiple low-order Zernike mode aberrations are applied simultaneously with a DM. Code we have developed performs two separate wavefront analyses corresponding to a highly robust (Shack-Hartmann) and highly sensitive (pyramid) mode and returns two sets of estimated amplitudes of the induced aberrations present. Our tests have experimentally confirmed the Hybrid Wavefront Sensor’s lenslet array allows wavefront analysis past the saturation point of its pyramid wavefront sensing mode resulting in high sensitivity to relatively weak aberrations while maintaining a high robustness to much stronger aberrations.

We are under integrating off-axis freeform mirrors for the KASI Deep Rolling Imaging Fast Telescope Generation 1 (KDRIFT G1) using a coordinate measuring machine and assembly jig. The telescope is a confocal off-axis freeform threemirror system designed for the detection of extremely low surface brightness structures in the sky. The optical specifications of the K-DRIFT G1 are as follows: the entrance pupil diameter is 300 mm, the focal ratio is 3.5, and the field of view is 4.43° × 4.43°. During the integration stage, we used a coordinate measuring machine to measure the positions of the mirrors, flexures, and bezels within a tolerance range. Following the system integration, we will measure wavefront errors at several edge fields using an interferometer at 633 nm. In this paper, we briefly present the current status of the K-DRIFT G1 and the future plans for the project.

UVO to Far-IR (UVO-FIR) mirror technology development project is a multiyear effort initiated in Fiscal Year (FY) 2022 to mature the Technology Readiness Level (TRL) of critical technologies required to enable ultra-stable telescope of the Habitable Worlds Observatory (HWO) mission. 2023/24 accomplishments include: continued investigations into gravity sag by comparing rotation test vs flip test, quantifying gravity sag as a function of temperature and designing mount for mirror whose G-sag with elevation angle is only coma. Significant progress in developing a methodology for specify optical surface microstructure, contamination cleanliness level and allowable micrometeoroid impacts. Support of HWO. And, a parametric cost model for x-ray telescopes and a parametric volume cost model for normal incidence telescopes

Optical alignment of the Coronagraph Instrument (CGI) was completed in time to begin its full-functional and environmental testing in late 2023 and its integration into the Roman Space Telescope (RST) in summer 2024. The optics of the CGI relay the optical pupil of the RST five times so that science operations, such as coronagraphy and wavefront control, can be conducted in the different internal pupil and image planes. Within the pupil relays, the CGI has multiple active optical assemblies, including a fast-steering mirror, a focus-control mirror, two deformable mirrors, and six precision alignment mechanisms that articulate different masks and apertures into the beam.

Initial alignment of the CGI optics was completed in the reverse direction, using a commercial dynamic Twyman-Green interferometer to measure the wavefront error through each relay as optics were added sequentially from back to front. The end-to-end wavefront error was initially verified using surrogate optics in place of the active optical assemblies, to allow their simultaneous development and test. Throughout alignment, pupil and image planes were referenced and coaligned optically using fiducials, including spherically mounted retroreflectors (SMRs) that were positioned by a laser tracker and measured by the interferometer camera.

Upon end-to-end alignment of the pupil-relay optics, the active optical assemblies were integrated and aligned individually, and the entire CGI alignment was then optimized. The CGI optical subsystem was also mapped to SMR fiducials, which will later be used to integrate CGI into the RST observatory and verify its alignment to the Telescope’s line of sight. This paper details the many alignment steps required to successfully achieve the performance criteria of the CGI.

When a telescope doesn’t reach a reasonable point spread function on the detector or detectable wavefront quality after initial assembly, a coarse phase alignment on-sky is crucial. Before utilizing a closed loop adaptive optics system, the observatory needs a strategy to actively align the telescope sufficiently for fine wavefront sensing (WFS). This paper presents a method of early-stage alignment using a stochastic parallel-gradient-descent (SPGD) algorithm which performs random perturbations to the optics of a three mirror anastigmat telescope design. The SPGD algorithm will drive the telescope until the wavefront error is below the acceptable range of the fine adaptive optics system to hand the telescope over. The focused spot size over the field of view is adopted as a feed parameter to SPGD algorithm and wavefront peak-to-valley error values are monitored to directly compare our mechanical capabilities to our alignment goal of diffraction limited imaging and fine wavefront sensing.

The success of the James Webb Space Telescope (JWST) ignited the scientific community to research a new era of telescope development. Furthermore, it is reasonable to assume that there will be more missions of a similar nature and purpose in the future. From now until the time the JWST is retired from service, updates in telescope, mounting, deployment, and even launch technology capabilities will be realized. This thesis outlines the opto-mechanical packaging of an Off-Axis -Three Mirror Anastigmat (OA-TMA). This optical system is designed to have an entrance pupil diameter of 150 mm, a focal length of 408.59 mm, and a 2.1⁰x2.05⁰ Field of View (FOV). The operational imaging waveband for this system is in the mid-wave infrared band. The selected camera for this system is the Teledyne Neutrino QX¹. Because the optical system is obscuration free, it results in a different packaging solution for space operation than that of the JWST. The primary requirement of this system is to fold into a smaller volume than its deployment configuration. The novel packaging method in this study resulted in a 66.7% reduction of volume.

Precision glass molding of optical lenses is similar to plastic injection molding, although a few fundamental differences exist between the two. One of the major disadvantages of the glass molding process over injection molding is the cycle time. The cycle time required for an injection-molded plastic lens can be less than 30 seconds, whereas an equivalent glass-molded lens may take anywhere from 15 to 30 minutes. Apart from the longer process times, the higher temperatures required by the glass molding process reduce the tool's lifetime thereby increasing the production costs. This paper presents a new glass press mold tooling that utilizes a multi-cavity approach with interchangeable mold pairs, enabling the production of multiple lenses in a single molding cycle. Further, the molding process as well as the tooling are optimized to achieve uniform accuracy and optical quality of the glass lenses across the mold plate.

The measurement of mid-spatial frequency (MSF) in ultra-precision machining is crucial for assessing the quality and performance of machined surfaces. MSF refers to the frequency range of surface irregularities between low-frequency form errors and high-frequency roughness. The sources that contribute to MSF errors during diamond turning are vibrations and dynamic instabilities, tool wear and deflection during cutting, inconsistent feed rates, variation in material properties, incorrect machine settings/process parameters, material removal mechanism employed (e.g., ductile or brittle removal). Controlling and measuring mid-spatial frequencies in the diamond-turning process is essential for meeting stringent optical specifications in various applications, such as lens manufacturing for imaging systems, telescopes, laser systems, etc. Inspecting MSF errors offline or after the manufacturing process is a common practice in the quality control of optical surfaces. However, there is a growing interest in incorporating on-machine metrology to detect and address MSF errors. One of the latest developments is a dual-mode on-machine metrology (OMM) system that simultaneously measures surface form and roughness without requiring the optical path's reconfiguration to switch between laser interferometer mode and LED interference microscopy mode. This study uses OMM to study the influence of process parameters and their impact on the mid-spatial frequencies during diamond turning. OMM provides real-time feedback, which helps in adjusting machining parameters to correct deviations and maintain the desired mid-spatial frequencies.

The introduction of laser-assisted technology by the OPTIMUS platform has enabled the efficient ultra-precision diamond turning of tungsten carbide, wherein a laser beam is precisely delivered through a diamond cutting tool to augment the diamond cutting edge with additional photon energy. This method effectively reduces the reliance on mechanical energy by a diamond cutting tool alone. Building on our prior research that explored the impact of tool rake angle on cutting depth under constant load, this study explores the combination of the optimal tool rake angle with relatively high laser powers useful for high Material Removal Rate (MRR). Initial results show the possibility to complete a pre-polish ready optic of nearly 5 mm diameter aperture within 20 mins versus an estimated 2 – 3 hours when compared to a similar process using traditional ultra-precision grinding, while preserving form irregularity and surface finish. With the MRR nearly 10 times higher than conventionally using ultra-precision grinding, laser assisted diamond turning of tungsten carbide is a revolutionary technology that can be considered for high-volume manufacturing of tungsten carbide molds used in glass optics. Furthermore, this study includes a comparison of advantages and limitations of each technology.

Achieving sub-nanometer precision in ion beam figuring (IBF) processes demands a comprehensive understanding and optimization of various key aspects, including metrology, dwell time optimization, velocity scheduling, positioning, and final inspection. In this study, these aspects are analyzed and discussed. Our solutions for the challenges in each aspect are highlighted, with implications for a wide range of applications requiring ultra-precise optical components.

We conducted research on ruled type grating, which is a method of manufacturing grating spectroscopic devices through mechanical processing. Grating is an optical component that specifies light through a multi-layer grid pattern structure and analyzes the characteristics of the measurement target using a spectrum according to the wavelength. The sharper the end of the blaze angle of the grating pattern designed for spectroscopy, the higher the reflectance and thus the higher optical efficiency. We adopted a cutting method through mechanical processing to sharpen the end of the blaze angle. In addition, the higher the refractive index, the smaller and lighter the spectroscopic equipment can be, so single crystal silicon material with a refractive index of n=3.5 (wavelength 1,000 nm) was used. However, Single crystal silicon material has low mechanical process ability due to its brittle nature with high hardness and low fracture toughness. To ensure process ability, we used ultra-precision grooving equipment to check the surface roughness tendency of the pattern surface according to the processing conditions of tool shape, tool feed speed, and cutting depth. Surface roughness was measured at several points on the pattern using a white light interferometer. As a result, we conducted basic research to derive the optimal processing conditions for Si gratings through the analysis of surface roughness trends and surface quality according to the processing conditions.

As wavefront quality demands tighten on space systems for applications such as astronomy and laser communication, mounting small optics such that the wavefront is undisturbed, positioning is adjustable and the design is producible, while surviving harsh space environments, is a continuing challenge. We designed multiple candidate flexure mounts to support small optics (up to 50 mm diameter, and over 100 grams) to survive the qualification and acceptance tests of small spacecraft and units as defined in ISO 19683 and a mounting structure which is adjustable in decenter [+/-0.5mm], tip/tilt +/-0.5deg, and piston [+/-0.25mm]. We will present design details along with measurements showing less than approximately lambda/10 wavefront contribution from the optic bonding process, along with thermal and multi-axis vibration test data showing the mounted optics survived the acceptance testing loads and are suitable for operation in a wide range of harsh environments.

Wire-bond quality monitoring is a critical step in the integrated circuit packaging process to ensure the reliability of the wire connections. This paper introduces a highly effective algorithm for the reconstruction of wire structures, facilitating the rapid 3D reconstruction and parameter measurement of wire bonding structures. The procedure starts by capturing optical slice images of the wires using oblique-illumination optical sectioning microscopy. This technique restricts the axial emission range of structures within the microscope's field of view, thereby improving the axial resolution of the target structures. Subsequently, we employ a block-boundary-based point cloud segmentation algorithm to enhance the separation efficiency of wire structures. This algorithm divides the collected three-dimensional point cloud data into fixed-size blocks and applies parallel processing to reduce the necessary computation time for connectivity domain statistics. Additionally, parallel processing at the segmentation boundaries addresses the merging needs of point cloud label data, achieving rapid localization of connected structures. This methodology substantially improves the separation efficiency of the bonding structures and augments their utility in semiconductor packaging. Ultimately, high-precision and efficient 3D parameter measurement of wire bonding structures is achieved. Theoretical analysis and experimental results confirm the effectiveness of the proposed method.