Fully scan-less three-dimensional imaging method was developed by use of an optical frequency comb. Interferometric measurement between chirped pulse train realized ultrafast information conversion between space, time, and color. Three-dimensional shape information of an object is thus obtained by two-dimensional spectral interference fringe image in a single pulse. With precisely controlled optical frequency combs, precise phase control of optical waves in a pulse train is utilized for all-optical Hilbert tansform to extract amplitude and phase of the obtained interference fringe image, thus two-dimensional spectroscopy is realized. With a monochromatic camera, three-dimensional image is obtained without any scanning. The developed method was applied to shape measurements of various targets with micrometer to nanometer resolution. Since pulse-to-pulse interferometer is utilized, a large object can be measured without losing high accuracy. Scan-less method can be applied to capturing moving target and ultrafast phenomena.

Manufacturing is progressing towards the utilisation of smart and autonomous manufacturing processes, facilitated by deeply integrated sensors providing rapid feedback, to enable tighter process control and ‘right first-time’ fabrication methods. Optical components are inherently heavy and bulky and consequently so is current optical instrumentation making it unsuitable to provide the in-situ measurements required to fully realise the vision of future manufacturing. Optical metasurfaces, being able to replicate the function of conventional optical elements, offer a step change in optical instrumentation size and weight. Here, we report on our monolithic metasurface confocal sensor that performs all the necessary optical manipulations to perform as an ultra-compact confocal sensor whilst also being rugged against misalignment. We have subsequently built on this approach to develop a tip-tilt displacement sensor which is achieved by interleaving three lenses into a single metasurface, each acting as a chromatic confocal sensor that is offset from each other.

To be updated

Recently, tomographic flow-cytometry in label-free modality has been demonstrated. The tomographic apparatus operates in Quantitative phase imaging (QPI) mode and gives the possibility to retrieve the 3D refractive index distribution of single cells flowing along a microfluidic channel. One of the challenging topic correlated to QPI is the need to extract subcellular compartments as QPI lacks the typical specificity guaranteed by standard fluorescence microscopy (FM). Here we show the possibility of retrieving the specific refractive index distribution of multiple sub-cellular organelles from the 3D tomograms of flowing cells. Furthermore, we show a novel model of representation and fruition of 3D tomograms, displayed in an immersive virtual reality (VR) environment. Thus, new scenarios can be opened not only for fruition but also for analyzing the quantitative measurements of the whole 3D structure of any and each cell.

While conventional ellipsometry is only applicable to homogeneous sample areas large enough to cover the illumination spot, imaging ellipsometry, combining ellipsometry and microscopy, offers a solution to this. It enables the local examination of polarization properties, yet it is not widely used in metrology, mostly due to a lack of proper evaluation methods. We discuss approaches for an advanced evaluation of imaging Mueller matrix ellipsometry for nanometrological applications. This encompasses ways to evaluate Mueller matrix images without 3D simulations, using techniques inspired by machine learning, as well as the algorithmic treatment of thermal instabilities. Also, we discuss the applicability of plasmonic lenses (PL) for the advancement of ellipsometric methods. We developed a new design for PLs to enable higher fabrication rates for possible applications. Simulations showed that PLs significantly enhance the sensitivity of ellipsometric measurements to subwavelength structures. This project 20FUN02 “POLight” has received funding from the EMPIR programme co-financed by the Participating States and from the European Union’s Horizon 2020 research and innovation programme.

An in-process monitoring of laser processing provides real-time feedback on the processing parameters. Thus, the optimal parameters for an unknown material can be determined with minimized prior measurements. Simultaneously measurements will reduce the processing time by allowing observation of the processed structure without the postprocessing. An acoustic method observes the deep site in optically opaque materials and is used in a complementary way to optical methods. In this research, laser drilling is controlled with the sound waves generated at a laser focusing point on and inside a target material. The axial position of the objective lens was controlled by the acquired excited sound, and the results of hole drilling according to changes in surface shape caused by ablation during processing are reported.

In this paper we continue to examine various types of optical frequency combs (OFCs) obtained with frequency down-conversion method in a frequency-shifted feedback laser operating in mode-locking regime without an external optical seeding. We propose to apply these combs to solve several problems associated with the feedback loop length and, consequently, time delay variations - for example, distance measurements, determination of the optical materials refractive index value and dispersion. The advantages of OFCs application obtained by the sequential frequency down-conversion method (dual- and quad-combs) in comparison with the initial OFCs, the spectral interval between the lines of which is determined only by the delay time in the feedback circuit, have been demonstrated. The sensitivity of the examined system to the optical path variation in the feedback loop is determined.

Nanopositioning and Nanomeasuring Machines (NPMM), developed at TU Ilmenau provides high-precision measurement and positioning of objects across 10 decades, from 20 pm resolution up to 200 mm measuring range. They are working on the basis of the error-minimal, extended three dimensional Abbe-comparator principle, with high precision fibre coupled laser interferometers and several optical, tactile and atomic force probes. The proof of the enormous accuracy repeatedly comes up against the limits of the realisation of representational standards. In addition to increasing the frequency stability of He-Ne lasers to 10-12, enormous progress has been made in correcting the refractive index of the laser wavelength. Measurement files of up to 6 TByte can be generated. Further development is moving in the direction of utilising the enormous precision of the machines for AFM tip-based and laser-based nanofabrication. The publication presents measurement and processing results and discusses the enormous possibilities of this new technology.

Current variable image magnification methods present problematic issues for high precision metrology instruments. This paper describes a novel approach to providing variable system magnification while avoiding those shortcomings. An optical zoom generally has multiple lens groups moving in concert to simultaneously adjust the effective focal length and maintain focus. Inevitably, the motion of the elements results in image drift and small variations in focus over the zoom range. An alternate approach using turreted fixed focal length lenses can have higher image quality but still suffers from image drift unless great care is taken in alignment of the individual lenses.

The variable-zoom method presented has a detector array with at least M*p pixels in each axis, where M is the maximum magnification and p x p is the size of the image array at each zoom. Pixels are binned based on the current magnification such that the final image size at each zoom magnification has a constant pixel array size. The fixed focal length imaging lens utilizes a variable aperture stop which is adjusted to maintain diffraction limited resolution. At low magnification the lens has a large field but requires lower resolution. As magnification increases the variable stop increases in size resulting in a smaller diffraction limited spot over a smaller FoV. The optical system can be much less complex than a traditional zoom and because there are no moving lenses, the image does not drift on the detector and there is no focal shift as the magnification changes.

This paper presents a methodology and related experimental results as a first attempt to answer the question of anuran audition and their ability to localize sound at acoustic frequencies they should not. An achiral digital holographic interferometer is designed so as to simultaneously measure the left and right tympanic vibrations on living specimen. The tympanic membranes are excited by an acoustic antenna including 22 loudspeakers emitting sound in the frequency range 1000 Hz to 3000 Hz. The first experimental results are presented.

The aim of this lecture is to show how the consideration of very specific measurement requirements, related to segmented surfaces and metasurfaces, has enabled a generalist multilateral shearing interferometer to evolve into new innovative devices. This has enabled state-of-the-art performance to be achieved, in particular by exploiting in the design a priori knowledge of the objects to be measured. Performance is illustrated here by a comparison of measurements on a canonical object, a PTT-111 deformable mirror from the company Iris AO, with a reference Phase Shifting Interferometer from the community.

In this presentation, we will present a light source based on adiabatic frequency conversion in millimeter-sized whispering gallery resonators (WGR) made from lithium niobate crystals, that was specifically developed to meet the stringent requirements of a digital holographic measurement system. Further on, first holographic measurements using this light source will be presented. Over 0.4 mW of average output power with 150 ns pulses and a central emission wavelength of 775 nm could be generated by the light source, with a linear tuning behavior of 66 MHz per Volt applied to the WGR.

This contribution discusses lateral resolution capabilities of CSI instruments based on the three-dimensional optical transfer function. The 3D transfer function combines the lateral spatial frequency transfer of a measured surface topography with axial spatial frequency contributions corresponding to the fringe frequencies of CSI signals. A broad bandwidth of fringe frequencies contributing to CSI signals can be achieved by both, low temporal coherence of the light source employed, or high numerical apertures, which reduce the longitudinal spatial coherence while enhancing the lateral resolution capabilities of an instrument. We first analyze theoretical aspects of lateral resolution in CSI using the Universal Fourier Optics (UFO) model and then validate our theoretical findings by experimental results using custom-built CSI systems of high NA. In addition, we introduce a CSI microscope equipped with immersion objectives to further improve the lateral resolution. Results based on separated phase irregularities demonstrate that scattering centers can be resolved even if their distance is less than the minimum distance predicted by the Abbe limit.

The paper discusses an alternative approach to the variable wavelength interferometry. The technique is based on specialized composition of two birefringent prisms that are inserted in a classical microscope with the Köhler illumination system. The optical system includes a continuously tuned light source and consists in advanced processing of sequentially recorded images at different wavelengths. The instrument is suitable for both transmitted and reflected-light modes and allows the user to measure optical and geometrical parameters of phase or reflective structures. This paper focuses on the reflected-light mode set-up, and measurements of waveplates and step height standards. The low uncertainty of the optical path difference is obtained by the continuous character of the light source and constitutes a key element of the system. In contrast to some previous presentations on the variable wavelength interferometry this paper demonstrates more profound nature of the phenomenon and a more precise algorithm for the fringe image processing.

One classical application of digital holographic interferometry is the measurement of shape from multi-wavelength recordings. One crucial step in the process is the refocusing to the correct image plane, where failure in finding the correct focus may lead to dimensional errors and lower accuracy. The use of sufficient metrics is therefore required. This paper proposes a new approach utilizing the linear relationship between in-plane speckle motion and defocus as a response to an induced phase gradient. Two simple metrics, based on the cross-correlation properties of the reconstructed speckle images, are proposed and evaluated utilizing both simulations and experiments. It is shown that both metrics perform well and manages to estimate the true reconstruction distance.

Optical profilometers perform an axial scan of an object to reconstruct its height map. Since the positioning errors of the scanner are directly transferred to the measurement, it is essential to minimize them. We present a zero-cost solution to suppress such errors, based on the computational analysis of two topographies that are identical except for an axial shift. The approach iteratively computes the a priori unknown nonlinearity operation of the scanner until the differences between the two corrected topographies are consistent. Here, we propose a new method for obtaining the topography pair. We use illumination from different LEDs, thereby exploiting the longitudinal chromatic aberration of the optical system to generate the axial shift. Interestingly, since only electronic switching of the LEDs is required, the approach enables to acquire the pair of topographies with a single scan. The method yields results comparable to measurements performed with a high-quality piezoelectric-based scanning system.

Professor James C. Wyant, founding dean and namesake of the James C. Wyant College of Optical Sciences at the University of Arizona, passed away on Friday, Dec. 8, 2023, in Tucson, after a valiant battle with Amyotrophic Lateral Sclerosis (ALS). He was 80 years old and had a deep and lasting impact on the international optics community and the field of optical sciences. His life touched countless souls and lives in a priceless manner. Someone’s life is so vast and profound that it cannot be encapsulated by a single person’s tribute. Upon the announcement of his passing, his colleagues, students, and friends left tributes at the Wyant College of Optical Sciences. Jim’s invaluable life is reflected in these tributes, which stand as the beautiful footprints of a giant.

Optical interferometry is widely used for high-precision displacement measurements in many areas of science and technology. Multiplexing interferometers to obtain interferometric phase measurements at multiple locations along a single beam is, however, a relatively new idea. This is possible using laser wavelength-modulated interferometric signal processing approaches such as the range-resolved interferometry (RRI) technique that can separately demodulate phase signals with sub-nanometer resolution from multiple interferometers with differing optical path lengths. Novel capabilities provided by RRI, include, for example, position or angular encoders with multiple degrees-of-freedoms that are multiplexed onto a single fiber-coupled access port. Also, the tomographic view of all signal sources present in an interferometric setup can be very useful for diagnostic purposes and allows additional absolute distance measurements. Furthermore, the ability to cleanly suppress multiple reflections allows for highly linear phase measurements. Therefore, range-resolved signal processing techniques open up novel solutions to existing measurement problems in precision engineering and advanced dimensional metrology.

Stitching interferometry is a powerful metrology technique used to measure the surface topography of optical mirrors with high precision and extended field of view. At the National Synchrotron Light Source II (NSLS-II), stitching interferometry with a Fizeau interferometer or a coherence scanning interferometer has been established to measure the surface topography of synchrotron mirrors. Stitching interferometry allows the inspection of synchrotron mirrors supplied by the optics vendors. Before the mirrors are installed into the synchrotron beamlines, they must be evaluated to ensure that they meet the stringent specifications (sub-nm RMS over the clear aperture). By employing stitching interferometry, surface deviations can be quantified to estimate the performance at a beamline. By analyzing the surface topography data collected with the stitching interferometry, we can use the surface residual errors with respect to the target shape to feedback to our developed deterministic fabrication method, Ion Beam Figuring (IBF), to further improve the mirror surface quality.

Cosine errors are ubiquitous in measurement science, referring to the proportional error that arises when the measurement device is incorrectly oriented. In the context of interferometry, this error arises when the orientation of the Fabry-Pérot cavity does not line up with the "true" measurement axis. While the cosine error can be corrected for if the degree of misalignment is known, any uncertainty in the misalignment will propagate to the length measurement, hence there is motive to minimise this uncertainty where it limits the overall measurement precision. This paper demonstrates the orientation of a plane-concave Fabry-Pérot interferometer to an external measurement axis using an external optical cavity. The purpose of this external cavity was to create a precise path reference with which to align the retro-reflection from the interferometer's plane mirror. Using this method, an interferometer was oriented relative to the central geometric axis of a calculable cross-capacitor within 8.3 μrad, with this axis defined using a custom sliding quadrant photo-detector centered between its four capacitor electrodes. The precision achieved with this technique is critical for meeting the few nF/F relative uncertainty target for this new capacitor, being built at the National Measurement Institute, Australia, which will ultimately improve the detection of systematic errors between calculable cross-capacitor and quantum-Hall realisations of the SI farad.

We present three digital twins for microscopy capable of simulating the image formation, the back focal plane formation and the near-field of confocal microscopes. For this, the light-surface interaction and the near-field are simulated using three different rigorous methods, the finite element method, the Fourier modal method and the boundary element method. The back focal plane formation and the image formation are simulated using three different Fourier optics implementations. The microscope modelling is done for ideal optical components, but can be extended to non-ideal optical components if the details of the optical components are known. The three models provide high accuracy and advantages with respect to the computational effort as a full 3D model is applied to 2D structures and the lateral scanning process of the confocal microscope is considered without repeating the time consuming rigorous simulation of the scattering process. The accuracy of the models are proven by comparison of the methods.

Three-dimensional transfer functions generally provide a comprehensive description of the transfer behavior of optical topography measuring instruments in spatial frequency domain. Recently, an analytical derivation of the transfer function has been achieved and based on this, the so-called universal Fourier optics (UFO) model has been developed for virtual coherence scanning interferometry (CSI). Especially for 3D surface topographies, simulation models suffer from long simulation times, even if the scattering process is considered approximately. The UFO model reduces the simulation time to a number of 2D FFTs (Fast Fourier Transforms) of a phase object enabling modeling of realistic 3D topographies in reasonable time for the first time. Besides CSI, also confocal microscopy (CM) is a widely used optical profiling technique and hence, this study presents a UFO model for CM considering lateral as well as depth scanning. The opportunities provided by modeling are demonstrated simulating confocal image stacks for realistic 3D surface topographies.

Optical metrology techniques allow for contactless surface measurement of three-dimensional objects at micro and nanoscale resolutions. Nevertheless, they often require acquiring multiple images from several focal planes, which is a slow process that severely limits topographic imaging speed. Here we introduce Encoded Search Focal Scan (ESFS), a technique capable of generating height maps of the sample from a significantly reduced number of images, down to single digits. Such a reduction enables commensurate speed improvements, allowing quasi-real-time topographic reconstructions. We implement ESFS using different system prototypes, including an imaging confocal microscope – used for reference –, a system based on an interferometric microscope objective, and a combination of an imaging confocal system with polarized detection. For each case, we analyze performance in terms of lateral resolution and acquisition speed. As our results demonstrate, ESFS opens the door to accurate topographic reconstructions of dynamic and rapidly moving systems.

Dynamics of a speckle pattern formed on the surface of a diffusely reflecting object is a source of valuable information about the changes that occur in the object. Laser speckle photometry extracts relevant information about the object from variations in speckle intensity. Speckle dynamics is visualized by means of an activity map, which renders the 2D distribution of a statistical parameter related to intensity changes. The contrast of the map is crucial for better detection of areas of different activity. Strong fluctuations in the map input data severely degrade the contrast. The main factors affecting the contrast are the processing algorithm and the speckle intensity distribution defined by the parameters of the optical system. The aim of this work is to find the optimal speckle pattern for laser speckle photometry based on the quality assessment of a 2D activity map estimated by correlation-based algorithms with averaging in the temporal or spatial domain. The study included simulation of correlated images with symmetric/asymmetric intensity distribution or at different speckle contrasts. We checked the quality of the obtained map for the case of 8-bit encoded, binary, or JPEG-compressed speckle images. We performed sensitivity evaluation of the method for non-destructive testing of samples under tensile extension.

Oxide-coated polymers hold promise as packaging materials that allow closed-loop recycling. In this context, accurate quality control of the coating thickness during the production process is essential. State-of-the-art measurement systems lack the compactness and scalability required for widespread applications inside production equipment. With an adapted spectral measuring range achieved through the implementation of optical filters, we apply infrared reflection-absorption spectroscopy (IRRAS) for inline quality control of nanometer-thin oxide coatings on polymers. For the commonly used SiO_x coatings with a thickness of 5 to about 200 nm, our sensor principle enables thickness measurements with a precision of better than 5 nm in two seconds. We show data from an industrial plasma coating system equipped with an array of sensors to measure the SiO_x coating thickness on parallelly processed cups during production. The results obtained from the simultaneous measurements of the coated cups effectively demonstrate the inline capability of our sensor.

In the wake of continuous miniaturization, optical metrology has solidified its role as an essential instrument in semiconductor manufacturing, chiefly due to its non-invasive, high-precision, and rapid measurement capacities. Particularly crucial in advanced techniques such as automated optical inspection (AOI), its significance grows with the rising demand for accurate 3D integrated circuit packaging characterization. This introduces notable challenges for optical metrology, which need addressing to meet rigorous in-line process demands. This talk aims to present an overview of key measurement methods in semiconductor fabrication, encompassing CD-SEM, X-ray or EUV scatterometry, reflectometry for optical critical dimension (OCD) metrology, AFM, advanced optics, and white light interferometry. The talk will share insights into the intrinsic limitations of these techniques, potential future innovations, and recent advancements in optical metrology. The session will conclude with a perspective on the evolution of these techniques amidst the prevailing technological constraints.

The first space-based gravitational wave observatory, the Laser Interferometer Space Antenna (LISA), will enable us to listen to gravitational waves between 100 μHz and 1 Hz. This ESA-led L-class mission will detect mergers involving ten thousand to ten million solar mass black holes throughout the universe, a million compact galactic binaries involving white dwarfs, neutron stars, and stellar mass black holes and many other gravitational wave signals. LISA will use laser interferometry to measure minuscule changes in the distance between six free falling test masses on board of three spacecrafts which form a 2.5Gm equilateral triangle. I will discuss the science case for LISA, the measurement principle, its technology readiness and the plans towards a launch in 2035.

Following a decade of unprecedented success through LIGO and Virgo’s observations of compact binary coalescences, gravitational wave astronomy is now recognized as a key tool in our continued efforts to understand the Universe and our place within it. Far from resting on their laurels though, the gravitational wave community is forging ahead with major plans for the future. The proposed “ultimate terrestrial gravitational wave detector facility” Cosmic Explorer recently received a boost with significant funding from the NSF to proceed with a conceptual design. This paper surveys the current state-of-the-art ground-based gravitational wave detector facilities, and their planned near-term upgrades. After motivating the next-generation Cosmic Explorer concept with a discussion of the key science targets, this paper describes some of the unique technical challenges it faces, including a focus on the ongoing optical design of Cosmic Explorer’s 40 km-scale laser interferometers.

Future X-ray telescopes will require measuring thousands of grazing-incidence mirrors with nanometer accuracy and high throughput. Fizeau interferometry will require accurately separating the reference surface from the surface under test, a challenging proposition for optical surfaces that are highly off-axis conics. We present a lateral shifting interferometry approach called Axial Shift Mapping (ASM), in which we measure the surface under test at multiple positions and numerically separate the reference and test surfaces. In this paper, we estimate the measurement accuracy that would be required for an exemplary 0.5 arcsecond half-power diameter angular resolution telescope. We mathematically describe the procedure for using ASM, plus a lateral shift, to extract the most important quantities for X-ray telescope mirrors: axial profile (including the quadratic component) and cone angle variation. We also conclude that the radius and cone angle of a mirror are unknowable with ASM alone.

This study proposes a novel approach in response to the persistent challenge of achieving precise autofocus in Digital Lensless Holographic Microscopy (DLHM). It involves employing an enhanced Bluestein algorithm to simulate DLHM holograms under a variety of conditions, spanning amplitude-only, phase-only, and amplitude-phase objects. These simulated holograms are used to assess the performance of autofocus metrics, including the Dubois and Spectral Dubois metrics, gradient and variance-based approaches, and lastly a learning-based model. By considering the variety of sample types and geometrical configurations, this study delves into the robustness and limitations of these metrics across diverse scenarios. This research reveals different performances depending on sample characteristics, offering valuable insights into selecting the most suitable autofocus metric, which is a demanding step in practical DLHM applications.

The automotive industry is permanently looking for increased productivity, improved flexibility, and customer satisfaction. Considering that the manufacturing of airbags is based mostly on textiles, there is a lot of manual work in the airbags process assembly; this is a major issue for productivity. The aim of the present, on-going work has been to study the benefits and limitations of utilizing machine learning (ML), video cameras, and robotic handling in order to reduce (or even eliminate) manual work in what concerns manufacturing processes of airbags. The approach has been based on using automation of processes in airbags manufacturing. In the initial stage of the in-development industrial process, the speed of the considered airbag manufacturing line was very close to a manual line. The paper briefly presents the optimization of the algorithms (using AI), the improvement of the process routes, as well as installing cameras to guide the robots to reach a better repeatability. This on-going procedure is briefly described. The final achieved results have included: 75% higher speed, therefore a productivity increase; 30% space reduction (parts/sqm); 100% quality check (i.e., all parts are 100% inspected); 0 NOK parts passed out of the production line; better quality results due to the dynamic positioning and better repeatability produced by using robotic systems; increased flexibility, because of the robotic system that can be programmed for more references; modularity. In conclusion, the fusion of ML, AI, robotic handling, and machine vision open a window for a new step in the industrial automation in the airbags/textile manufacturing, promising a productivity increase, a higher quality, less manual work, and better sustainability.

The dynamic system analysis capability of dynamic mode decomposition (DMD) technique is utilized for the phase retrieval in phase shifting interferometry. The DMD decomposes the spatio-temporal interferometric data into three distinct spatial fields (modes) which represent the background intensity and complex amplitudes associated with the interferogram. The phase estimate can be obtained from one of these modes which oscillates with a temporal frequency equal to the phase shift. Two DMD-based algorithms are reported which operate with minimum four interferograms, and accumulated phase shift of π. The comparative study among the DMD-based and the least-squares, PCA, 4-bucket, 5-bucket and 7-bucket algorithms performed in function of signal-to-noise ratio, phase-shift miscalibration, and amplitude and frequency of vibration demonstrates the suitability of proposed algorithm in practical scenarios.

Deep learning-enabled multiplexed fringe projection profilometry allows to achieve high-resolution and highspeed 3D imaging at near-one-order of magnitude-higher 3D frame rate with conventional low-speed cameras. Then the method is demonstrated by measuring 2 transient scenes: rotating fan blades and bullet fired from a toy gun, at kHz using cameras of around 100 Hz.

Fringe projection profilometry (FPP) is a well-established and noncontact optical method for tridimensional shape measurement. As an FPP technology, simultaneously dual fringe projection moiré profilometry (SDFPMP) increases twice the measurement sensitivity by taking advantage of two illumination directions (projectors) and the phase demodulation of the moiré patterns. In general, the SDFPMP technique is simple and low-cost; however, the projector-camera system usually has a nonlinear intensity response; hence, it distorts the acquired fringe patterns. This intensity alteration, namely gamma distortion, is translated into the appearance of undesired high-order harmonics, so they can impede reaching high accuracy measurements while not removing them adequately. In this manuscript, we study the purely temporal phase demodulation in SDFPMP to cope with the gamma distortion via harmonic rejection. Our analysis depicts that the optimal phase demodulation requires 3(𝐾 + 2) fringe patterns being 𝐾 the highest-order, distorting harmonic. Moreover, we show that when the system’s gamma is around 2.0, we can effectively reduce the gamma error amplitude to 0.001 radians by selecting 𝐾 = 2. Numerical experiments demonstrate the approach’s feasibility in overcoming gamma distortion.

Phase measuring deflectometry is a shape measurement technique for specular surfaces, based on the deflection of light rays coming from active patterns generated by a display. To obtain sufficient data for shape reconstruction, additional information must be provided for regularization. Active display registration is a regularization technique where the display is moved, and two cameras are used to register its position and shape using stereo matching. For measuring high curvature specular surfaces, the large field of view of both cameras must substantially overlap, which limits the setup geometry. In this work, we propose using only one camera for registration. We achieve this with an algorithm that utilizes a geometric model of the display. We show experimental results and compare both display registration methods.

In optical interferometry, phase-shifting algorithms can calculate the phase maps of the geometrical properties from measured samples with high accuracy. The phase-shifting algorithms require several interferograms captured from dynamic adjustable interferometers, with shifting occurring at uniform intervals. It is crucial to maintain the uniform shift intervals in phase-shifting algorithms because nonuniformities in intervals cause nonlinearities in the system and degrade the accuracy of measurement. However, experimental conditions inevitably introduce errors into dynamic adjustments due to environmental uncertainties. To address these drawbacks, we propose a novel method, shifted-interferogram generator, that eliminates the need for dynamic adjustments by utilizing a static optical interferometer with a single frame of interferogram. The proposed interferogram shifter involves capturing a single frame of an interferogram and employing deep learning to generate interferograms with ideal shifting intervals. For assessment of the proposed method, a single interferogram indicating surface shape of an optical flat was captured by Fizeau interferometer and given to the shifted-interferogram generator. The generated shifted interferograms were compared with the ideally shifted interferograms which contain exact shifting intervals and the results shows high similarities. Subsequently, the generated interferograms were used to extract phase, resulting in significantly improved accuracy comparable to more complex multi-step phase-shifting algorithms. This approach not only enhances measurement accuracy but also simplifies experimental setups, reducing susceptibility to environmental uncertainties.

Accurate form measurements for aspherical and freeform surfaces are in high demand and tilted-wave interferometry is a promising method to fulfill this need. However, interferometric form measurement methods for curved surfaces are sensitive to positioning errors of the surface under test, especially along the optical axis. To investigate the influence, we have measured the drift of two different positioning hexapods and simulated the influence of the drift on the form reconstruction of the surface under test. The simulation results were compared to repeated form measurements of a surface under test with the tilted-wave interferometer.

Optical retarders are essential for controlling polarization. Usual retarders are defined by two parameters: retardance and fast axis azimuth. Most characterizing procedures can determine only one of these parameters. Other methods require previously characterized retarders, are complex, or are restricted to certain experimental conditions. In this work, we present a simple interferometric method to fully characterize a retarder. It consists of using a dual path interferometer with polarization control. When the retarder is rotated, the interference pattern shifts, and the retarder parameters can be related to those shifts. We present two procedures to measure the pattern shift and calculate the retarder parameters, where each one presents different advantages.

This paper describes a setup aimed at measuring the so-called Tilt-To-Length (TTL) coupling in the optical benches of the LISA mission. The TTL is the coupling of the angular jitter of any optical setup into the optical path length between its input and output pupils. This might be deleterious in laser ranging experiments and must be evaluated for further compensation. The setup is made of two laser beams, one features an angular jitter that mimics the input beam as seen from the jittering bench under test (BUT), the other is aligned to the optical axis of the BUT and provides a phase reference for the jittering beam. The induced phase variations between both beams detected at the BUT’s output pupil gives access to the TTL coupling. The “TTL probe” must feature a negligible residual TTL coupling which implies a micrometric accuracy in the centering of the setup pupil, the beams and the angular jitter associated pivot point. The setup integrates optical masks as a link between the setup optical reference frame to its mechanical reference frame, together with position memories and servo-loops for the beam’s alignment. We show that the stability, the accuracy, and the noise floor of the setup is compliant with the LISA specifications for the TTL mitigation, although it makes use of off-the-shelf components and is operated in a standard environment laboratory.

We present Diffractio, an open-source Python package for the analysis of diffraction and interference phenomena in Optics, both within the scalar and vector optics approach. It is based on three main modules: Sources (for generation of light sources), Masks (for generation of optical elements, amplitude and phase masks, diffractive optical elements, and polarizers for vector optics) and Fields (for propagation, data analysis, storage, visualization, and video rendering). Within the scalar wave optics approach, Diffractio implements several algorithms for plane-to-plane propagation, such as the Fast Fourier Transform (FFT), Rayleigh-Sommerfeld propagation (RS), and Chirped Z-Transform (CZT). Additionally, Diffractio contains algorithms for step-by-step propagation, including Beam Propagation Method (BPM) and Wave Propagation Method (WPM). Our package further extends its capabilities to vector wave propagation using the Vector Fast Fourier Transform (VFFT), Vector Rayleigh-Sommerfeld (VRS), and Vector Chirped Z-Transform (VCZT) algorithms. All these algorithms are adaptable to various dimensions for faster computations: X, XY, XZ, and XYZ. In addition, the graphical representation functions included in Diffractio help to better analyze the fields and the associated variables, such as field and intensity distributions. Besides, when a deeper polarization analysis is necessary, Diffractio works seamless with our Py-Pol open-source package. This comprehensive suite of functionalities within the Diffractio library, positions it as a valuable tool for scientists, teachers, and engineers engaged in the study and application of Optics, offering well-established solutions for scalar and vector wave optics analysis down to the mesoscale. The software is available from the Python Package Index (PyPI) and Github repositories, at https://pypi.org/project/diffractio/ and https://github.com/optbrea/diffractio, respectively. Additionally, an online documentation resource is available at https://diffractio.readthedocs.io/en/latest/. This documentation illustrates the operation of the library and its practical application in physical optics with numerous examples. Users can take advantage of these instructional materials to gain a profound understanding of the software’s functionalities and implement it in their optical analyses.

Digital holographic microscopy (DHM) has a wide variety of applications in biomedical sciences. Here we examine the use of an off-axis holographic system to monitor bacterial growth in commercially available ibidi micro-fluidic chambers. The imaged volume spans roughly 120 x 120 x 200 μm3, at 50x magnification. By use of an off-axis reference wave and some standard numerical filtering operations it is possible to recover the complex amplitude and thus the phase of the object wave. Two strains of bacteria are used in the research study: Escherichia coli and Staphylococcus warneri with dimensions around 1-4 microns. Examining these samples, showed that through the use of phase compensation techniques, the method can sustain an average Signal-to-Noise ratio (SNR) of around 5, allowing for the use of a simple thresholding algorithm for cell counting. In addition, the cell count dynamics determined using this method reflect the exponential increase of dilution steps very well, when compared against hypothetical cell counts. Details of the system operation, including a discussion of the signal processing routines, together with modifications to the general optic design of DHM systems are presented.

Inelastic scattering of light by acoustic waves from a medium are known as Brillouin scattering. This effect was demonstrated by Léon Brillouin. Laser beam with high power enables Brillouin scattering thanks to acoustic vibrations in polymethyl methacrylate (PMMA). This phenomenon is known as stimulated Brillouin scattering. In our case we use a commercial bench based on the J. R. Sandercock multipass tandem interferometer design. Our study aims to gain confidence in knowing if the result given by the bench can lead to a more precise determination of the order of magnitude of the uncertainty associated with the result obtained in terms of deviation to the optical carrier. We determine the uncertainty to be ± 0.26% at 2 σ based on a modern approach. We intend to present it at the conference to give indications on the expected uncertainty terms of the microwave signal deviation of the carrier at 532 nm, characterising PMMA.

The integration of microspheres within the instruments of optical metrology and mask-less lithography could already show a significant enhancement of their lateral resolution. Exposing complex large structures exploiting this high resolution requires the lateral movement of the microsphere over the substrate. Challenging remains the accurate lateral and axial positioning of the microsphere ensuring the constant exposure conditions at every point. Preserving the advantage of optical instruments to not actually contact the specimen, the microsphere must be kept at a nanometer-close, yet constant distance from the surface. Here, we introduce the, to our best knowledge, novel approach to combine the principle of the differential confocal microscope with a scanning microsphere. This produces a differential signal towards the surface allowing a nanometer-sensitive and fast control of the axial position of the microsphere above the substrate. In preliminary experiments we show the repeatable pick-up of microspheres and their precise lateral scanning using a nanopositioning and nanomeasuring machine as well as axial depth responses and differential signals from the realized microsphere assisted differential confocal probe.

There are manifold challenges in the measurement of photonic products with white light interferometry (WLI), especially where near- or inline measurement is needed. To face these challenges, new approaches in software and hardware are required. In this presentation, the use of a new white light interferometry sensor with advanced features and relevant unique capabilities is highlighted, with applications in the fields of optical and Photonics Integrated Circuit (PIC) development and production.

The OpenRRI project is an open-source project offering a free and ready-to-use post-processing interferometer implementation based on the Range-Resolved Interferometry (RRI) technique. It is provided with convenient software functionalities as well as a guide for setting up and operating RRI interferometers. The main advantage of pseudo-heterodyne interferometers, such as those using the RRI approach, compared to classic homodyne or heterodyne signal processing, is their cost-effectiveness while maintaining the ability to perform relative displacement measurements with sub-nanometer precision. The interferometer uses a fiber-coupled laser diode with a wavelength of 1550 nm, which is sinusoidally modulated by laser injection current. At the fiber-coupled, collimated measurement head, the interference between the back reflection of the free-space beam reflected by the target mirror and the fiber tip reflection leads to an interferometric signal at the optical detector that can be evaluated. Additionally, the RRI concept, unlike most pseudo-heterodyne interferometric techniques, could simultaneously interrogate multiple interference sources within a single optical setup, for example if multiple semi-transparent glass surfaces are present. The interferometric signal acquired by the optical detector then can be demodulated using the software functionalities provided by the OpenRRI project. In the first part, this contribution focuses on the working principle of the RRI and the features provided by the OpenRRI system. The second part then presents a novel interferometric setup based on the RRI technique, enabling interferometric point-to-point measurement outside the optical axis.

For manufacturing of high-value components, such as in the aerospace, automotive, shipbuilding and nuclear power industries, there is a significant demand for integrated traceable measurement to provide fast feedback during the manufacturing processes. Most modern machine tools are equipped with a probing system. However, one of the key challenges is that the traceability of measurement on a machine tool is not ensured yet, and therefore, the measurement results are not reliable for process control and product geometry verification. A laser tracker is a portable optical measurement system and capable of performing high accuracy and long range 3D measurements. As such, it is a suitable alternative solution for large component measurement. The aim of this paper is to test measurement uncertainties for a large component using different methods, including use of tactile on-machine tool probing and optical laser tracker, in ‘shop floor’ conditions. The measurement results have been verified using a large gantry coordinate measuring machine (CMM).

Online monitoring of water pollutants is of great importance for the early detection of contaminants and improving the quality of drinking water. We showcase a smart design of a miniaturized, low-cost, versatile, and handheld optofluidic chip for characterizing microplastics (MPs) in water, which are a potential threat to our environment. The chip encompasses all the required optics for guiding the light to/from the microfluidics, all sandwiched together as a unique miniaturized system. Size and concentration of MPs are characterized by measuring the static light scattering (SLS) signal at two different angles: 0 and 40 degrees. In fact, the concentration of MPs is obtained by observing the SLS signal only at one angle, while for the size of MPs one needs to calculate the variation of signal at two concentrations. In a next step, the performance of the optofluidic chip is benchmarked against a commercial bulky system. The latter works based on a technique called “Goniophotometry”, capable of measuring the SLS signal at a broad range of scattering angles between - 90 and +90 degrees. Chemometric algorithms like Principal Component Analysis (PCA) and Linear Discriminant Analysis (LDA) are used to extract the size and concentration of MPs in water using the bulky system. The different sizes and concentrations of MPs are prepared using commercial Polystyrene (PS) beads. It is shown that the developed optofluidic microsystem provides a comparable performance to the commercial bulky machine and is thus a significant step towards the online monitoring of water pollutants, like MPs, in drinking water.

The fringe pattern denoising and inpainting operations are crucial for the accurate phase retrieval in the phase-based optical measurement techniques. In this work, a Fourier-Bessel series expansion (FBSE)-based algorithm is proposed for the fringe pattern denoising and inpainting. The FBSE provides a compact representation of wide-band fringe pattern for the effective fringe signal denoising. The Bessel functions are used for the accurate reconstruction of non-stationary fringe signal even in the events of loss of fringe data at some object points. A comparative study between the FBSE, windowed Fourier filtering and partial differential equation-based methods is presented for the fringe pattern denoising. The simulation and experimental results indicate the suitability of the proposed method in practical applications.

With the advancing development of the semiconductor industry, optical resolution of EUV lithography has shrinked to 13nm. In the preceding inspection process of unpatterned silicon wafer, the resolution of nano-metrology of 12.5nm has been realized. For better improving the resolution of nano-metrology in unpatterned silicon wafer, more precise modelling of scatterometry is necessary. Metrology of silicon wafer is standardized with Polystyrenelatex (PSL) and metallic nano-spheres. Rayleigh scattering of PSL and metallic nano-particles in the three dimensional space is modeled and analyzed with Bidirectional Reflectance Distribution Function. Given the setting up of a simplified dark field inspection system and the established Rayleigh scattering BRDF model, the impact of different parameters on the polarized Rayleigh scattering of nano-particles on the silicon wafer are evaluated. The comprehensive analysis in this article provides a theoretical foundation for the following system design and upgradation.

The cavity mirror in the resonant cavity is the core device of the system, defects and contamination of the cavity mirror will directly affect the accuracy of the instrument. With the use of limited cavity length in cavity ring-down spectroscopy (CRDS) technology, which is targeted to achieve tens of thousands of meters of absorption path length, is widely used in atomic absorption spectroscopy, medical diagnosis, life support systems in the space and other fields. CRDS in the use of passive resonant cavity, is more vulnerable to the scattering impacts of defects. In the measurement process, due to the accumulation of contaminants in the gas and the damage of the laser beam to the high reflectance film of the reflector, the optical path characteristics of the cavity will be affected by the scattered stray light, which will reduce the ring-down time, decrease the absorption path length in the resonant cavity, and affect the measurement accuracy of the instrument. In this paper, the impact of defect from micrometer to submicrometer magnitudes on CRDS accuracy is analyzed. The electric field characteristics in the defective resonant cavity was simulated using Comsol Multiphysics software, and it was concluded that the scattering of pits and particles shifts the cavity polarization and disrupts the cavity resonance. A standard particle deposition system, PDS, and a laser damage pit were utilized in the experiments to simulate particles and pits, respectively. The different defect categories of the cavities were calibrated by a high-precision 3D measurement system. Cavity mirrors in different defect magnitudes are sequentially combined to form a resonant cavity. By analyzing the correspondence between CRDS measurement accuracy and defects magnitude from micron to submicron, it is concluded that when the pollution particles and pit defects of the cavity mirror are larger than the critical value, the reduction of ring down time will seriously affect the accuracy of the instrument. The study of scattering correlation model of cavity defects establishes a quantitative relationship between cavity defects and CRDS measurement accuracy, which lays a foundation for the improvement of instrumental measurement accuracy.