Proceedings Volume 12223

Interferometry XXI

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Proceedings Volume 12223

Interferometry XXI

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Volume Details

Date Published: 6 October 2022
Contents: 7 Sessions, 22 Papers, 20 Presentations
Conference: SPIE Optical Engineering + Applications 2022
Volume Number: 12223

Table of Contents

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Table of Contents

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  • Front Matter: Volume 12223
  • On the Fringe
  • Characterization and Techniques
  • Vikram Lecture
  • Biological Measurement Techniques
  • Novel Techniques
  • Poster Session
Front Matter: Volume 12223
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Front Matter: Volume 12223
This PDF file contains the front matter associated with SPIE Proceedings Volume 12223, including the Title Page, Copyright information, Table of Contents, and Conference Committee listings.
On the Fringe
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Heterodyne interferometer microscopy for high precision surface measurement
Laser Doppler vibrometer (LDV) is typically used to detect and measure vibrations and dynamics of mechanical structures in a non- contacting and non-destructive way. Eckermann et al. proposed 1993 in a patent a technique to apply LDV to surface topography measurements. In this paper we explore the application of the technique to surface-topography analysis, providing the potential of axial resolution in the picometer regime for lateral resolutions defined by a confocal microscope. By moving the sample with high speed perpendicularly through the focused beam of the LDV, the topography of the surface will change the optical pathlength between LDV and specimen which the LDV measures with broad bandwidth. The advantage of this approach is that mechanical vibrations of the specimen and the stage can be filtered as they appear in a much lower frequency range as the topography information of the specimen. For the preliminary setup, we used a commercially available LDV (Polytec OVF-303s) focused on the sample with a 50x microscope objective. The sample is a chrome-covered Siemens Star Target with a step height of 140.8 nm. The high relative speed of the topography with up to 2.5 m/s is realized by rotating the sample using a speed-controlled servo motor. With this preliminary setup, we achieved a focus diameter of 1.4 µm and an axial resolution of 1.53 nm in the full bandwidth of 250 kHz.
Wavefront sensor fusion via shallow decoder neural networks for aero-optical predictive control
Shervin Sahba, Christopher C. Wilcox, Austin McDaniel, et al.
Sensor limitations often result in devices with particularly high spatial-imaging resolution or high sampling rates but not both concurrently. Adaptive optics control mechanisms, for example, rely on high-fidelity sensing technology to predictively correct wavefront phase aberrations. We propose fusing these two categories of sensors: those with high spatial resolution and those with high temporal resolution. As a prototype, we first sub-sample simulations of the Kuramoto-Sivashinsky equation, known for its chaotic flow from diffusive instability, and build a map between such simulated sensors using a Shallow Decoder Neural Network. We then examine how to fuse the merits of a common sensor in aero-optical sensing, the Shack-Hartmann wavefront sensor, with the increased spatial information of a Digital Holography wavefront sensor, training on supersonic wind-tunnel wavefront data provided by the Aero-Effects Laboratory at the Air Force Research Laboratory Directed Energy Directorate. These maps merge the high-temporal and high-spatial resolutions from each respective sensor, demonstrating a proof-of-concept for wavefront sensor fusion for adaptive optical applications.
Vision ray metrology: a new versatile tool for the metrology and alignment of optics
A novel Vision ray metrology technique is reported that estimates the geometric wavefront of a measurement sample using the sample-induced deflection in the vision rays. Vision ray techniques are known in the vision community to provide image formation models even when conventional camera calibration techniques fail. This work extends the use of vision rays to the area of optical metrology. In contrast to phase measuring deflectometry, this work relies on differential measurements, and hence, the absolute position and orientation between target and camera do not need to be known. This optical configuration significantly reduces the complexity of the reconstruction algorithms. The proposed vision ray metrology system does not require mathematical optimization algorithms for calibration and reconstruction – the vision rays are obtained using a simple 3D fitting of a line.
Microwave-photonic dynamic frequency-swept interferometry for fast ranging
Frequency-swept interferometry (FSI) is intrinsically suitable for static ranging. For dynamic targets, its ranging accuracy is deteriorated by the Doppler phenomenon, and its measurement rate is restricted by the frequency sweep rate (usually kHz level), which prevents the acquisition of accurate time-varying distance details. To solve the problems, a novel microwave-photonic dynamic FSI (MP-DFSI) for fast ranging is proposed in this paper, which uses a single-frequency laser and an electro-optic modulator (EOM) to constitute a dual-sweep laser to provide two ideal mirrored laser sweeps. The instantaneous phases of the MP-DFSI signals are modulated by both the target distance and velocity in measurement, we investigate and model the modulation relationship, present a new data fusion demodulation method for high-accuracy fast ranging, which can effectively eliminate the Doppler error and recover the continuously-varying distance at each sampling point during a whole frequency-sweep cycle. Numerical verifications demonstrate that the measurement rate of the proposed MP-DFSI can reach 10 MHz with 1 μm ranging accuracy, showing the MP-DFSI has the ability of high-accuracy fast-ranging for dynamic targets.
Characterization and Techniques
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Characterization of surface texture-measuring optical microscopes using a binary pseudo-random array standard
Ulf Griesmann, Keiko Munechika, T. Brian Renegar, et al.
Accurate topography measurements of engineered surfaces over a wide range of spatial frequencies are required in many applications. The instrument transfer function (ITF) of the microscope used to characterize the surface topography must be taken into consideration to ensure that the height, or depth, of features with higher spatial frequency content is not underestimated. This applies especially when comparing surface topography measurements made by different types of microscopes. We discuss ITF measurements of a confocal microscope and an interferometric microscope using a binary pseudo-random array (BPRA) standard. BPRA standards are surfaces designed to have constant inherent power spectral density (PSD) over the spatial frequency passband of a microscope. The ITF of a microscope can thus be derived from a PSD measurement of a BPRA standard in a straight-forward manner. We further show how BPRA standards can be used as efficient diagnostic tools to characterize aspects of the imaging performance of topography-measuring microscopes.
Binary pseudo-random array standards for calibration of 3D optical surface profilers used for metrology with aspheric x-ray optics
Keiko Munechika, Weilun Chao, Scott Dhuey, et al.
High-accuracy surface metrology is vitally important in manufacturing ultra-high-quality free-form mirrors designed to manipulate x-ray light with nanometer-scale wavelengths. The current capabilities and possibility for improvements in x˗ray mirror manufacturing are limited by inherent imperfections of the integrated metrology tools. Metrology tools are currently calibrated with super-polished flat test-standard/reference mirrors. This is acceptable for fabrication of slightly curved x-ray optics. However, for even moderately curved aspherical x-ray mirrors the flat-reference calibration is not sufficiently accurate. In the case of micro-stitching interferometry developed for surface measurements with curved xray mirrors, the tool aberration errors are known to be transferred into the optical surface topography of x-ray mirrors. Our approach to improvement of the metrology is to thoroughly calibrate the measuring tool and apply the results of the calibration to gain the reliability of the metrology via calibration-based deconvolution of the measured data. Thus, we explore the application of a recently developed technique for calibrating the instrument’s transfer function (ITF) of 3D optical surface profilers to the metrology with significantly curved x-ray optics. The technique, based on test standards structured as two-dimensional (2D) binary pseudo-random arrays (BPRAs), employs the unique properties of the BPRA patterns in the spatial frequency domain. The inherent 2D power spectral density of the pattern has a deterministic whitenoise-like character that allows direct determination of the ITF with uniform sensitivity over the entire spatial frequency range and field-of-view of an instrument. The high efficacy of the technique has been previously demonstrated in application to metrology with flat and slightly curved optics. Here, we concentrate on development of an efficient fabrication process for production of highly randomized (HR) BPRA test standards on flat and 500-mm spherical optical substrates. We also compare and discuss the results of the ITF calibration of an interferometric microscope when using the HR BPRA standards on flat and curved substrates.
Calibration, modeling, parameterization, and verification of the instrument transfer function of an interferometric microscope
P. Z. Takacs, S. Rochester, I. Lacey, et al.
Interferometric microscopes are used to measure surface roughness, from which the computed power spectral density function can be used to extract bandwidth-limited values of the various surface properties, such as root-mean-square (rms) height and slope errors. Measurements with a microscope equipped with different objectives that have an overlapping spatial frequency range usually give different rms results over the common frequency bandwidth. This is a result of different instrument transfer functions (ITFs) that attenuate spatial frequencies by different amounts over the overlapping range. We report on the use of binary pseudo-random array (BPRA) standards to characterize the ITF of an interferometric microscope with the various objectives. We use a simple model of a 1D binary Results show that the spectrum for an undersampled array is a cosine function, rather than a straight line, constant white noise spectrum. We have an analytical model of the ITF that includes the effects of an obscured aperture and defocus, in addition to the usual parameters of numerical aperture, wavelength, and sampling period. In addition, the model includes the effect of aliasing of spatial frequency components beyond the Nyquist back into the sub-Nyquist region. We compare the model PSD predictions to the measurements performed with different objectives. Departures of the measured PSDs from the model predictions indicate that there are higher-order ITF corrections yet to be identified and included in the model.
Fast locally adaptive method for optical fringe pattern filtering
Mikołaj Rogalski, Jędrzej Szpygiel, Antonio Cicone, et al.
We present an algorithm for robust and automatic optical fringe pattern filtration called locally adaptive filtration (LAF). We compare it with the reference method and show the advantages of LAF filtration, especially in terms of low-contrast (low SNR and high background modulation) fringes filtration.
Determination of the characteristics of a self-built coherence scanning interferometer with a universal calibration artefact
Matthias Eifler, Julian Hering, Georgis Bulun, et al.
ISO 25178-601 ff. define specific characteristics of individual measuring principles including coherence scanning interferometry (CSI) in -604. In the present study, we use a previously developed Universal Calibration Artefact to examine which additional information about CSI-specific metrological characteristics can be obtained by the evaluation of its measured data. In doing so, a self-built CSI as an exemplary measuring instrument is examined in a case study to test which of the material measures type ASG, AFL, ARS, ACG, AIR according to ISO 25178-70 and the chirp material measure (CIN) can be used to acquire detailed information about the characteristics that are specific to the optical setup of a CSI and their possible deviations. It can be shown that additional information about many characteristics including the properties of the light source like the wavelength or bandwidth, or information about the optical setup like the numerical aperture, can be extracted from a series of only seven measurements of the Universal Calibration Artefact.
Vikram Lecture
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Holography: a 60 years journey with outstanding achievements
In this paper we look back to 60 years of holograpy. Special attention is given to its application for non-destructive testing and experimental stress analysis. Across these years both techniques have shown to be versatile tools for the solution of many inspection problems. Their main advantages are the non-contact nature, the non-destructive and areal working principle, the fast response, high sensitivity, resolution and accuracy. In contrast to conventional techniques such as classical interferometry, the holographic principle of wave front storage and reconstruction made it possible to investigate objects with rough surfaces that experience any change by temporal wave front division. The paper reviews the history of holographic metrology, honors the inventors of the main principles, and shows exemplary applications. However, the main focus is on modern developments that are inspired by the rapid technological process in sensing technology and digitization, current applications and future challenges.
Biological Measurement Techniques
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High-speed live cell interferometry for functional drug sensitivity screening of bioprinted tumor organoids (Conference Presentation)
As interest grows in using three-dimensional (3D) tumor organoids as models for drug discovery and precision medicine, platforms for the reliable functional testing and analysis of these organoids are needed. Our group previously developed high-speed live cell interferometry (HSLCI), a powerful high-throughput functional drug screening platform which employs automated, repeated quantitative phase imaging (QPI) to longitudinally track drug-induced changes in biomass accumulation dynamics over time. Here, we present a method for the automated bioprinting of 3D tumor organoids coupled with real-time, highly parallel biomass quantification using HSLCI, and demonstrate its utility for drug screening.
Metrological assessment of reconstruction accuracy in holographic tomography (Conference Presentation)
Malgorzata Kujawinska, Michal Ziemczonok
3D quantitative phase imaging (3D QPI) delivers volumetric information about the refractive index distribution within microobjects. Such imaging and measurement capabilities are of great interest for technical and biomedical applications, yet there are no standardized methods for testing and reporting metrological performance. In this paper we present methodology for metrological evaluation of instruments based on single wavelength and hyperspectral holographic tomography in biomedical applications. The methodology entails suitable phantoms, quality assessment metric and easily reproducible protocol that is attainable for both numerical and experimental analysis. We demonstrate its applicability by comparing simulated reconstructions with measurements from 3 holographic tomography systems.
Digital holographic microscopy for volumetric, three-dimensional characterization of bacterial motility
Jian Gao, Jarl Carnahan, Gladys Alexandre, et al.
Digital holographic microscopy (DHM) has extensive applications in measuring the movement/dynamics of various particles (e.g., tracer particles and biological samples). Specifically, inline DHM has been used for different types of bacteria, but few have explored its application to soil bacteria, whose participation in metabolic processes and interaction with plant tissues affect plant growth in the rhizosphere. In the present study, we have developed a DHM instrument and GPU-enabled hologram processing software to retrieve three-dimensional (3D) motility data of free-swimming Azospirillum brasilense, a model soil bacterium. The dimensions of the sample volume are 0.69 mm × 0.59 mm in the in-plane directions and 1.00 mm in the depth direction, respectively. With a 20X magnification and a 12 frames per second imaging rate, the moving bacteria are spatiotemporally resolved. Firstly, the raw holograms are preprocessed to enhance the interference fringes of the bacteria. Subsequently, by volumetric reconstruction, thresholding, and segmentation, the 3D coordinates of each bacterium recorded in the hologram are extracted. Finally, the coordinates determined in sequential holograms are linked using particle tracking to form the trajectories. The characteristics extracted from the 3D trajectories quantitatively revealed the differences in the motility patterns of the wildtype and mutant strains of the bacteria, providing unique insights on the dominant motility patterns, which are otherwise unavailable from conventional microscopy. Therefore, we have demonstrated the capabilities of our DHM system as a powerful tool for studying the chemotaxis of soil bacteria involved in the interaction with plant roots.
Longitudinal xenograft zebrafish investigation using polarization-sensitive Jones-matrix optical coherence tomography (Conference Presentation)
The zebrafish is a valuable animal model in pre-clinical cancer research. Optical coherence tomography (OCT) is a non-invasive optical imaging technique, which provides a label-free and three-dimensional method to investigate the tissue structure. Jones-matrix OCT (JM-OCT) is a functional extension of conventional OCT, to gain additional tissue specific contrast by analyzing the polarization states of the back-scattered light. In this work we present the longitudinal investigation of in vivo wildtype and a tumor xenograft zebrafish model using our JM-OCT prototype. The scattering and depth-resolved polarization properties in control versus tumor regions were analyzed and compared to results obtained from histology.
Common-path grating-based interferometers with altered temporal and spatial coherence of illumination for quantitative phase microscopy and tomography
We discuss implementations of a straightforward common-path interferometric system within the microscope setup to allow for quantitative phase contrast imaging. Fringe pattern generation is based on the interference between +1 and -1 diffraction grating orders. Limited angle optical diffraction tomography is realized upon illuminating the sample under varying angles and reconstructing a 3D refractive index distribution via filtered back-projection. Due to equalized optical path of both conjugate +1/-1 beams temporal coherence alteration can be easily implemented with benefits of coherent noise minimization (reducing speckles and parasitic interferences). Presented setups employ single microscope objective in an open-top configuration allowing for comfortable sample operation. Proposed 2D/3D grating-based common-path quantitative phase imaging systems are limited to sparse samples, as +1/-1 interference needs to superimpose object replica and object-free area, however.
Single-shot quantitative phase microscopy in common-path configuration
Brandon Norton, Bryce Evans, Juan Viveros-Escoto, et al.
Quantitative phase Microscopy is an advantageous technique to retrieve 3D cell information to estimate cell dry mass and morphology. A popular method is to implement this setup in a common path configuration because it is a system robust to vibrations, and it combines phase contrast imaging with phase shifting techniques to provide high-accuracy measurements. However, this approach requires using a spatial light modulator and at least three images to calculate the phase. In our approach, we leverage the optical anisotropy of liquid crystal materials and a polarized camera to obtain four phase-shifted images simultaneously.
Novel Techniques
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Vibration insensitive fiber optic spectral interferometric probe for metrology of topography and thickness of multilayer samples
We describe a metrology system allowing for the reduction of the errors caused by vibration of the production floor and allowing for measurements of the thickness of wafers in motion. This is accomplished by performing simultaneous measurements of spectra containing interference signals containing distance information using two or more probes positioned on both sides of the measured wafer on the same detector at the same time.
A new optical diagnostics tools for grading additive manufactured parts
James Trolinger, Jian Gao, Cecil Hess, et al.
In previous papers, we described a diagnostics tool for additive manufacturing products that is based on the concept that the acoustical/vibrational spectrum of an object can be used as a unique signature that characterizes the material and geometry of a product sufficiently to enable its comparison with a perfect reference to identify anomalies. This enables a user to identify rogue parts, such as defective, counterfeit, suspicious or problem parts such as defective or failing to meet specifications. The instrument produces a signature by measuring, with a laser Doppler vibrometer, the vibration of surface points on the part while it is energized by a swept frequency, piezo-electric exciter. Since its first introduction, additional research and development has enhanced, automated, and moved the instrument to a new level in terms of capability and ease of use. This paper describes the latest enhancements, including improved procedures and automation to enable use by an unsophisticated user with minimum training. The latest version provides automatic signal processing and comparison of acoustical signatures of reference and test objects that provide a quantitative grade for the object in terms of material properties, geometrical anomalies, and defects. This is achieved with specially developed algorithms that employ unique types of correlation of vibrational spectra taken from different objects or spectra produced by a simulation of a perfect object. The instrument can quickly produce an optimized correlation coefficient that serves as a numeric grade for a part for identifying suspicious or problem parts such as counterfeits, defective, or failing to meet specifications. The user can set acceptance criteria and initiate a pass or fail signal that can be used for large quantity inspections. Such an instrument is expected to find widespread applications in the AM industry.
Optomechanical technologies for broadband inertial sensing
Accelerometers are a vital component in inertial sensing and geodesy, gravitational physics, seismic noise detection, hydrology, and other fields requiring precision measurements. Our group develops compact low and high frequency optomechanical inertial sensors to measure acceleration for various applications. Our sensors measure the linear displacement of an oscillating test mass with displacement laser interferometers that are fiber-coupled or free space. The observed external acceleration is recovered from the displacement of the test mass. Our compact 5 Hz resonator will operate as a relative gravimeter and be read out by a compact, highly sensitive free-space heterodyne laser interferometer. It has demonstrated low mechanical losses with quality factors above 4.77 × 105 and mQ-products greater than 1200 kg. Our millimeter scale higher frequency resonators are made of fused silica for operation at room temperature and Si for operation at cryogenic temperatures. They will be readout with fiber based Fabry-Perot cavities or waveguide ring resonators that are currently under development. We are working to fabricate the Si resonators and are optimizing the process using Bosch and cryo-Si DRIE etching. Here, we report our progress on design and fabrication along with preliminary measurement results for all resonator prototypes.
A nanophotonic interferometer for small particle detection
A. Ghaffari, K. Do, S. Kashani, et al.
The transmission of light through sub-wavelength apertures (zero-mode waveguides, ZMW) in metal films is wellexplored. It introduces both an amplitude modulation as well as a phase shift to the transmitted oscillating electromagnetic field. We propose a nanophotonic interferometer by bringing two zero-mode waveguides in proximity and monitoring the distribution of light in the back-focal plane of the collecting microscope objective. We demonstrate that both an asymmetry induced by the binding of a quantum dot in one of the two ZMW, as well as a asymmetry in ZMW diameter yield qualitatively similar deflection patterns. Using ZMW pairs with diameter asymmetries, we find that the complex pattern of the transmitted light can be quantified through a scalar measure of asymmetry along the symmetry axis of the aperture pair. We find that this scalar asymmetry is a monotonous function of the diameter difference of the two apertures.
Variable shearing holography with geometric phase elements
In this paper, we demonstrate the recording of shear interferograms using diffractive polarization gratings and reconstruct complex wavefields using a known optimization algorithm. We validate the reconstruction of a complex wavefield by recording the object wave at a defocused distance and numerically refocusing the reconstructed wavefield. Finally, we discuss the impact of the shear selection strategy and aperture selection using the information density function and demonstrate this by reconstructing complex wavefields using experimental data.
Poster Session
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Investigation on output variations of ring laser gyroscope in the presence of non-ideal sinusoidal dithering
W.-S. Choi, C.-J. Kim
Frequency lock-in is the most principal phenomenological feature to be characterized and eliminated for the development of high precision ring laser gyroscope (RLG). As an effective method to solve the lock-in induced problem, sinusoidal dithering by mechanical manner has been proposed and has widely used successfully to date. However, in real applications, pure-sinusoidal dithering is nearly impossible, so additional nonlinear factors should be considered for modeling of dithered RLG. In this work, output variations of RLG in the presence of non-ideal sinusoidal dithering are investigated by performing numerical experiments.
Design and implementation of a fiber-fed Fourier transform spectrograph for astronomical applications
The Fourier transform spectrograph (FTS) is one important tool that has been used to analyze and characterize the radiated energy distribution of the stellar objects through an atmosphere. Most of the current spectrographs were installed at the telescope focal plane of the telescope, which required the space and complexity of alignments. The implementation of a fiber to feed the light from the telescope has been implemented to overcome those limitations. However, a small flux due to the single point field of view becomes a main challenge of this system. In this work, we report the development of the laboratory prototype of a fiber-fed FTS by using off-the-shelf components specifically designed for the Thai National Telescope (TNT). The method used to process the data relies on the cubic spline interpolation for resampling of both scientific and metrology interferograms and producing the spectrum from the raw measurements. The current maximum optical path difference is about 30 mm with an achievable spectral resolving power higher than 19,000 based on the instrument line shape of the system. The results obtained by concentrating the Sun light with the signal-to-noise-ratio (SNR) greater than 20 are presented. We also present the preliminary results of the low flux detection from a dim halogentungsten source comparable to the magnitude of a bright star in the order of a few nano-watts. The implementation of a phase-lock amplifier has been investigated to detect the signal and improve the signal-to-noise-ratio of the spectrum.
Modified Fizeau interferometer with the polynomial and FFT smoothing algorithm
The modified Fizeau interferometer that allows to diagnose plane and spherical optical elements with the diameter ranging from 10 to 100 mm is discussed. The modified method of interference patterns reconstruction based on reference lines is described. Two algorithms — the algorithm of 4th order polynomial smoothing and the algorithm of fast Fourier transform are implemented. The modified method allowed to increase the reliability of interferometric pattern reconstruction and suppress the influence of incoming noise. Accuracy of the measurements is about λ/10 (λ=0.63 um).