Artifact-Resilient Real-Time Holography Victor Chu, Oscar Pueyo-Ciutad, Ethan Tseng, Florian Schiffers, Grace Kuo, Nathan Matsuda, Alberto Redo-Sanchez, Douglas Lanman, Oliver Cossairt, Felix Heide ACM Transactions on Graphics, 2025 Holographic near-eye displays promise unparalleled depth cues, high-resolution imagery, and realistic three-dimensional parallax at a compact form factor, making them promising candidates for emerging augmented and virtual reality systems. However, existing holographic display methods often assume ideal viewing conditions and overlook real-world factors such as eye floaters and eyelashes—obstructions that can severely degrade perceived image quality. In this work, we propose a new metric that quantifies hologram resilience to artifacts and apply it to computer generated holography (CGH) optimization. We call this Artifact Resilient Holography (ARH). We begin by introducing a simulation method that models the effects of pre- and post-pupil obstructions on holographic displays. Our analysis reveals that eyebox regions dominated by low frequencies—produced especially by the smooth-phase holograms broadly adopted in recent holography work—are vulnerable to visual degradation from dynamic obstructions such as floaters and eyelashes. In contrast, random phase holograms spread energy more uniformly across the eyebox spectrum, enabling them to diffract around obstructions without producing prominent artifacts. By characterizing a random phase eyebox using the Rayleigh Distribution, we derive a differentiable metric in the eyebox domain. We then apply this metric to train a real-time neural network-based phase generator, enabling it to produce artifact-resilient 3D holograms that preserve visual fidelity across a range of practical viewing conditions—enhancing both robustness and user interactivity.
Influence of some acquisition parameters in non-line-of-sight imaging F. Christnacher, M. Laurenzis, S. Schertzer, Alexander Spaett, A. Redo-Sanchez, D. Gutierrez Proceedings of SPIE the International Society for Optical Engineering, 2025 Over the past few years, Non-Line-of-Sight (NLOS) scene reconstruction algorithms have made significant progress, transforming our ability to reconstruct environments and scenes that are hidden from the direct view. These algorithms employ sophisticated techniques such as f-k migration, back-propagation, or phasor-field models to reconstruct the scene and reveal hidden objects. However, a major challenge persists: the time required to acquire the vast amounts of data needed to generate a high-quality, high-resolution scene reconstruction. High-resolution scene reconstructions necessitate extensive data collection, often involving measurements of multi-scattered light, leading to substantial data volumes. This results in prolonged acquisition times and considerable computational costs. Therefore, a pressing issue is how to reduce acquisition time without sacrificing the accuracy and resolution of the final reconstruction. To tackle this challenge, we have systematically analyzed the impact of each of these acquisition parameters to understand their influence on both acquisition time and data-transient quality. Our goal is to identify the most significant parameters and adjust them to achieve the desired trade-off between speed and accuracy. One of the most pressing issues is how to reduce the acquisition time without compromising the accuracy and resolution of the final reconstruction. To get closer to real-time processing, it is essential to carefully consider the parameters involved in the acquisition phase. Key parameters including the sensor pixel calibration, the exposure time and number of images per frame, the camera field-of-view (FOV) and focus adjustment, all play a critical role in both the quality of the reconstruction and the time required to acquire the necessary data. Optimizing these acquisition parameters is key to improving the efficiency of the scene reconstruction process.
Time-Gated Polarization for Active Non-Line-Of-Sight Imaging Oscar Pueyo-Ciutad, Julio Marco, Stephane Schertzer, Frank Christnacher, Martin Laurenzis, Diego Gutierrez, Albert Redo-Sanchez Proceedings SIGGRAPH Asia 2024 Conference Papers SA 2024, 2024 Our polarized NLOS imaging setupHidden object Analyzer
Cohesive framework for non-line-of-sight imaging based on Dirac notation Albert Redo-Sanchez, Pablo Luesia-Lahoz, Diego Gutierrez, Adolfo Muñoz Optics Express, 2024 The non-line-of-sight (NLOS) imaging field encompasses both experimental and computational frameworks that focus on imaging elements that are out of the direct line-of-sight, for example, imaging elements that are around a corner. Current NLOS imaging methods offer a compromise between accuracy and reconstruction time as experimental setups have become more reliable, faster, and more accurate. However, all these imaging methods implement different assumptions and light transport models that are only valid under particular circumstances. This paper lays down the foundation for a cohesive theoretical framework which provides insights about the limitations and virtues of existing approaches in a rigorous mathematical manner. In particular, we adopt Dirac notation and concepts borrowed from quantum mechanics to define a set of simple equations that enable: i) the derivation of other NLOS imaging methods from such single equation (we provide examples of the three most used frameworks in NLOS imaging: back-propagation, phasor fields, and f-k migration); ii) the demonstration that the Rayleigh-Sommerfeld diffraction operator is the propagation operator for wave-based imaging methods; and iii) the demonstration that back-propagation and wave-based imaging formulations are equivalent since, as we show, propagation operators are unitary. We expect that our proposed framework will deepen our understanding of the NLOS field and expand its utility in practical cases by providing a cohesive intuition on how to image complex NLOS scenes independently of the underlying reconstruction method.
Non-line-of-sight imaging in the presence of scattering media using phasor fields Pablo Luesia, Miguel Crespo, Adrian Jarabo, Albert Redo-Sanchez Optics Letters, 2022 Non-line-of-sight (NLOS) imaging aims to reconstruct partially or completely occluded scenes. Recent approaches have demonstrated high-quality reconstructions of complex scenes with arbitrary reflectance, occlusions, and significant multi-path effects. However, previous works focused on surface scattering only, which reduces the generality in more challenging scenarios such as scenes submerged in scattering media. In this work, we investigate current state-of-the-art NLOS imaging methods based on phasor fields to reconstruct scenes submerged in scattering media. We empirically analyze the capability of phasor fields in reconstructing complex synthetic scenes submerged in thick scattering media. We also apply the method to real scenes, showing that it performs similarly to recent diffuse optical tomography methods.
Towards standardisation of contact and contactless electrical measurements of CVD graphene at the macro-, micro- and nano-scale Christos Melios, Nathaniel Huang, Luca Callegaro, Alba Centeno, Alessandro Cultrera, Alvaro Cordon, Vishal Panchal, Israel Arnedo, Albert Redo-Sanchez, David Etayo, Montserrat Fernandez, Alex Lopez, Sergiy Rozhko, Oihana Txoperena, Amaia Zurutuza, Olga Kazakova Scientific Reports, 2020 Graphene has become the focus of extensive research efforts and it can now be produced in wafer-scale. For the development of next generation graphene-based electronic components, electrical characterization of graphene is imperative and requires the measurement of work function, sheet resistance, carrier concentration and mobility in both macro-, micro- and nano-scale. Moreover, commercial applications of graphene require fast and large-area mapping of electrical properties, rather than obtaining a single point value, which should be ideally achieved by a contactless measurement technique. We demonstrate a comprehensive methodology for measurements of the electrical properties of graphene that ranges from nano- to macro- scales, while balancing the acquisition time and maintaining the robust quality control and reproducibility between contact and contactless methods. The electrical characterisation is achieved by using a combination of techniques, including magneto-transport in the van der Pauw geometry, THz time-domain spectroscopy mapping and calibrated Kelvin probe force microscopy. The results exhibit excellent agreement between the different techniques. Moreover, we highlight the need for standardized electrical measurements in highly controlled environmental conditions and the application of appropriate weighting functions.
Mapping the conductivity of graphene with Electrical Resistance Tomography Alessandro Cultrera, Danilo Serazio, Amaia Zurutuza, Alba Centeno, Oihana Txoperena, David Etayo, Alvaro Cordon, Albert Redo-Sanchez, Israel Arnedo, Massimo Ortolano, Luca Callegaro Scientific Reports, 2019 Electronic applications of large-area graphene films require rapid and accurate methods to map their electrical properties. Here we present the first electrical resistance tomography (ERT) measurements on large-area graphene samples, obtained with a dedicated measurement setup and reconstruction software. The outcome of an ERT measurement is a map of the graphene electrical conductivity. The same setup allows to perform van der Pauw (vdP) measurements of the average conductivity. We characterised the electrical conductivity of chemical-vapour deposited graphene samples by performing ERT, vdP and scanning terahertz time-domain spectroscopy (TDS), the last one by means of a commercial instrument. The measurement results are compared and discussed, showing the potential of ERT as an accurate and reliable technique for the electrical characterization of graphene samples.
THz to inspect graphene and thin film materials Alvaro Cordon, M. Castrillo, A. G. Miguel Laso, Israel Arnedo, Luis Miranda, Cristian Martinez, Andrea Ines, David Etayo, Montserrat Fernandez, Pablo Rodriguez, Elena Taboada, Albert Redo-Sanchez International Conference on Infrared Millimeter and Terahertz Waves Irmmw Thz, 2019 In this paper, we present a system that provides meso-scale characterization of thin film materials, covering the gap between nano-scale and macro-scale methods. Nano-scale methods are slow and cannot characterize large surfaces. Macroscale methods generate characterization that averages the magnitudes and, thus, cannot provide localized information. Our system works in reflection as opposed to state-of-the-art methods and provides mobility, carrier density, and conductance maps in the THz range. Moreover, it can be integrated with reactors and enables monitoring of the fabrication of materials in real-time, supporting, for instance, the production of graphene at industrial scale.
GRACE: Developing Electrical Characterisation Methods for Future Graphene Electronics L. Callegaro, C. Cassiago, A. Cultrera, V. D'Elia, D. Serazio, M. Ortolano, M. Marzano, O. Kazakova, C. Melios, F. Raso, L. Matias, A. Zurutuza, A. Centeno, A. Redo-Sanchez, A. Kretinin, K. Sann-Ferro, A. Fabricius, G. Weking, W. Bergholz, N. Fabricius CPEM 2018 Conference on Precision Electromagnetic Measurements, 2018 GRACE - Developing electrical characterisation methods for future graphene electronics is a 2016 Normative Joint Research Project of the European Metrology Programme for Innovation and Research. The project focuses on the measurement of the electrical properties of graphene. Its objectives are to develop validated measurement methods and protocols, including fast-throughput examples. The work is performed in collaboration with international standardisation committees, with an aim to initiate and develop dedicated documentary standards.
Quality assessment of terahertz time-domain spectroscopy transmission and reflection modes for graphene conductivity mapping David M. A. Mackenzie, Patrick R. Whelan, Peter Bøggild, Peter Uhd Jepsen, Albert Redo-Sanchez, David Etayo, Norbert Fabricius, Dirch Hjorth Petersen Optics Express, 2018 We present a comparative study of electrical measurements of graphene using terahertz time-domain spectroscopy in transmission and reflection mode, and compare the measured sheet conductivity values to electrical van der Pauw measurements made independently in three different laboratories. Overall median conductivity variations of up to 15% were observed between laboratories, which are attributed mainly to the well-known temperature and humidity dependence of non-encapsulated graphene devices. We conclude that terahertz time-domain spectroscopy performed in either reflection mode or transmission modes are indeed very accurate methods for mapping electrical conductivity of graphene, and that both methods are interchangeable within measurement uncertainties. The conductivity obtained via terahertz time-domain spectroscopy were consistently in agreement with electrical van der Pauw measurements, while offering the additional advantages associated with contactless mapping, such as high throughput, no lithography requirement, and with the spatial mapping directly revealing the presence of any inhomogeneities or isolating defects. The confirmation of the accuracy of reflection-mode removes the requirement of a specialized THz-transparent substrate to accurately measure the conductivity.
THz photonics Chi Lee Microwave Photonics Second Edition, 2017
High speed imaging with CW THz for security Qian Song, Albert Redo-Sanchez, Yuejin Zhao, Cunlin Zhang Proceedings of SPIE the International Society for Optical Engineering, 2009
2-D acoustic phase imaging with millimeter-wave radiation IEEE Transactions on Microwave Theory and Techniques, 2009
