Optics and Sensing Laboratory
The Optics and Sensing Laboratory supports research and development of new algorithms for image processing, enhancement and denoising, the integration of sensing systems of different types (stereo, video, range, etc.), new sensors and algorithms for computational photography and astronomy, and the development of real-time sensing systems for robotic platforms.
Members:
| Tübingen |
| Tübingen | |
| 1713 | |
| Tübingen |
| Tübingen | |
| +49 7071 6011709 | |
| Tübingen |
| Tübingen |
| +49 7071 601 1770 | |
| Tübingen |
Alumni:
Fiber-based shape sensor
2021-09-29
Grassroots initiative into developing a novel shape probe made out of a multimode optical fiber.
26 results
2024
Reinforcement learning in cold atom experiments
Reinschmidt, M., Fortágh, J., Günther, A., Volchkov, V.
nature communications, 15:8532, October 2024 (article)
Cold atom traps are at the heart of many quantum applications in science and
technology. The preparation and control of atomic clouds involves complex
optimization processes, that could be supported and accelerated by machine
learning. In this work, we introduce reinforcement learning to cold atom
experiments and demonstrate a flexible and adaptive approach to control a
magneto-optical trap. Instead of following a set of predetermined rules to
accomplish a specific task, the objectives are defined by a reward function.
This approach not only optimizes the cooling of atoms just as an experi-
mentalist would do, but also enables new operational modes such as the
preparation of pre-defined numbers of atoms in a cloud. The machine control
is trained to be robust against external perturbations and able to react to
situations not seen during the training. Finally, we show that the time con-
suming training can be performed in-silico using a generic simulation and
demonstrate successful transfer to the real world experiment.
Fiber-Optic Shape Sensing Using Neural Networks Operating on Multispecklegrams
Cao, C. G. L., Javot, B., Bhattarai, S., Bierig, K., Oreshnikov, I., Volchkov, V. V.
IEEE Sensors Journal, 24(17):27532-27540, September 2024 (article)
Application of machine learning techniques on fiber speckle images to infer fiber deformation allows the use of an unmodified multimode fiber to act as a shape sensor. This approach eliminates the need for complex fiber design or construction (e.g., Bragg gratings and time-of-flight). Prior work in shape determination using neural networks trained on a finite number of possible fiber shapes (formulated as a classification task), or trained on a few continuous degrees of freedom, has been limited to reconstruction of fiber shapes only one bend at a time. Furthermore, generalization to shapes that were not used in training is challenging. Our innovative approach improves generalization capabilities, using computer vision-assisted parameterization of the actual fiber shape to provide a ground truth, and multiple specklegrams per fiber shape obtained by controlling the input field. Results from experimenting with several neural network architectures, shape parameterization, number of inputs, and specklegram resolution show that fiber shapes with multiple bends can be accurately predicted. Our approach is able to generalize to new shapes that were not in the training set. This approach of end-to-end training on parameterized ground truth opens new avenues for fiber-optic sensor applications. We publish the datasets used for training and validation, as well as an out-of-distribution (OOD) test set, and encourage interested readers to access these datasets for their own model development.
Polarization-based non-linear deep diffractive neural networks
Kottapalli, S. N. M., Schlieder, L., Song, A., Volchkov, V., Schölkopf, B., Fischer, P.
AI and Optical Data Sciences V, PC12903, pages: PC129030B, (Editors: Ken-ichi Kitayama and Volker J. Sorger), SPIE, January 2024 (conference)
2023
Glare Removal for Astronomical Images with High Local Dynamic Range
Bastelaer, M., Kremer, H., Volchkov, V., Passy, J., Schölkopf, B.
IEEE International Conference on Computational Photography (ICCP), pages: 1-11, IEEE, July 2023 (conference)
Multiplane Diffractive Acoustic Networks
Athanassiadis, A. G., Schlieder, L., Melde, K., Volchkov, V., Schölkopf, B., Fischer, P.
IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, 70(5):441-448, IEEE, March 2023 (article)
2022
Bichromatic state-dependent disordered potential for Anderson localization of ultracold atoms
Lecoutre, B., Guo, Y., Yu, X., Niranjan, M., Mukhtar, M., Volchkov, V., Aspect, A., Josse, V.
European Physical Journal D, 76, pages: 218, 2022 (article)
The ability to load ultracold atoms at a well-defined energy in a disordered potential is a crucial tool to study quantum transport, and in particular Anderson localization. In this paper, we present a new method for achieving that goal by rf transfer of atoms in an atomic Bose-Einstein condensate from a disorder-insensitive state to a disorder-sensitive state. It is based on a bichromatic laser speckle pattern, produced by two lasers whose frequencies are chosen so that their light-shifts cancel each other in the first state and add up in the second state. Moreover, the spontaneous scattering rate in the disorder-sensitive state is low enough to allow for long observation times of quantum transport in that state. We theoretically and experimentally study the characteristics of the resulting potential.
Diversifying the geosciences in higher education: a manifesto for change
Caitlyn A. Hall, , Sam Illingworth, , Solmaz Mohadjer, , Mathew Koll Roxy, , Craig Poku, , Frederick Otu-Larbi, , Darryl Reano, , Mara Freilich, , Maria-Luisa Veisaga, , Miguel Valencia, , Morales, J.
Geoscience Communication, 5(5):275–280, 2022 (article)
There is still a significant lack of diversity and equity in geoscience education, even after decades of work and widespread calls for improvement and action. We join
fellow community voices in calls for improved diversity, equity, inclusion, and justice in the geosciences. Here, in this manifesto, we present a list of opportunities for educators to bring about this cultural shift within higher education: (1) advocating for institutional change, (2) incorporating diverse
perspectives and authors in curricula, (3) teaching historical and socio-political contexts of geoscience information, (4) connecting geoscience principles to more geographically diverse locations, (5) implementing different communication styles that consider different ways of knowing and learning, and (6) empowering learner transformation and agency.
Capturing and Inferring Dense Full-Body Human-Scene Contact
Huang, C. P., Yi, H., Höschle, M., Safroshkin, M., Alexiadis, T., Polikovsky, S., Scharstein, D., Black, M. J.
In 2022 IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR 2022), pages: 13264-13275, IEEE, Piscataway, NJ, IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR 2022), June 2022 (inproceedings)
Inferring human-scene contact (HSC) is the first step toward understanding how humans interact with their surroundings. While detecting 2D human-object interaction (HOI) and reconstructing 3D human pose and shape (HPS) have enjoyed significant progress, reasoning about 3D human-scene contact from a single image is still challenging. Existing HSC detection methods consider only a few types of predefined contact, often reduce body and scene to a small number of primitives, and even overlook image evidence. To predict human-scene contact from a single image, we address the limitations above from both data and algorithmic perspectives. We capture a new dataset called RICH for “Real scenes, Interaction, Contact and Humans.” RICH contains multiview outdoor/indoor video sequences at 4K resolution, ground-truth 3D human bodies captured using markerless motion capture, 3D body scans, and high resolution 3D scene scans. A key feature of RICH is that it also contains accurate vertex-level contact labels on the body. Using RICH, we train a network that predicts dense body-scene contacts from a single RGB image. Our key insight is that regions in contact are always occluded so the network needs the ability to explore the whole image for evidence. We use a transformer to learn such non-local relationships and propose a new Body-Scene contact TRansfOrmer (BSTRO). Very few methods explore 3D contact; those that do focus on the feet only, detect foot contact as a post-processing step, or infer contact from body pose without looking at the scene. To our knowledge, BSTRO is the first method to directly estimate 3D body-scene contact from a single image. We demonstrate that BSTRO significantly outperforms the prior art. The code and dataset are available at https://rich.is.tue.mpg.de.
2021
Invited perspectives: Building sustainable and resilient communities – recommended actions for natural hazard scientists
Gill, J. C., Taylor, F. E., Duncan, M. J., Mohadjer, S., Budimir, M., Mdala, H., Bukachi, V.
Natural Hazards and Earth System Sciences, 21(1):187-202, 2021 (article)
Using paired teaching for earthquake education in schools
Mohadjer, S., Mutz, S., Kemp, M., Gill, S., Ischuk, A., Ehlers, T.
Geoscience Communication, 4(2):281-295, 2021 (article)
In this study, we have created 10 geoscience video lessons that follow the paired-teaching pedagogical approach. This method is used to supplement the standard school curriculum with video lessons, instructed by geoscientists from around the world, coupled with activities carried out under the guidance of classroom teachers. The video lessons introduce students to the scientific concepts behind earthquakes (e.g. the Earth’s interior, plate tectonics, faulting, and seismic energy), earthquake hazards, and mitigation measures (e.g. liquefaction, structural, and non- structural earthquake hazards). These concepts are taught through hands-on learning, where students use everyday materials to build models to visualize basic Earth processes that produce earthquakes and explore the effects of different hazards. To evaluate the effectiveness of these virtual lessons, we tested our videos in school classrooms in Dushanbe (Tajikistan) and London (United Kingdom). Before and after the video implementations, students completed questionnaires that probed their knowledge on topics covered by each video, including the Earth’s interior, tectonic plate boundaries, and non-structural hazards. Our assessment results indicate that, while the paired- teaching video lessons appear to enhance student knowledge and understanding of some concepts (e.g. Earth’s interior, earthquake location forecasting, and non-structural hazards), they bring little change to their views on the causes of earthquakes and their relation to plate boundaries. In general, the difference between UK and Tajik students’ level of knowledge prior to and after video testing is more significant than the difference between pre- and post-knowledge for each group. This could be due to several factors affecting curriculum testing (e.g. level of teachers’ participation and classroom culture) and students’ learning of content (e.g. pre-existing hazards knowledge and experience). To maximize the impact of school-based risk reduction education, curriculum developers must move beyond innovative content and pedagogical approaches, take classroom culture into consideration, and instil skills needed for participatory learning and discovery.
2020
Temporal variations in rockfall and rock-wall retreat rates in a deglaciated valley over the past 11 k.y.
Mohadjer, S., Ehlers, T. A., Nettesheim, M., Ott, M. B., Glotzbach, C., Drews, R.
Geology, 48(6):594-598, 2020 (article)
2019
On the Transfer of Inductive Bias from Simulation to the Real World: a New Disentanglement Dataset
Gondal, M. W., Wüthrich, M., Miladinovic, D., Locatello, F., Breidt, M., Volchkov, V., Akpo, J., Bachem, O., Schölkopf, B., Bauer, S.
Advances in Neural Information Processing Systems 32 (NeurIPS 2019), pages: 15714-15725, (Editors: H. Wallach and H. Larochelle and A. Beygelzimer and F. d’Alché-Buc and E. Fox and R. Garnett), Curran Associates, Inc., 33rd Annual Conference on Neural Information Processing Systems, December 2019 (conference)
Ultracold atoms in disordered potentials: elastic scattering time in the strong scattering regime
Signoles, A., Lecoutre, B., Richard, J., Lim, L., Denechaud, V., Volchkov, V., Angelopoulou, V., Jendrzejewski, F., Aspect, A., Sanchez-Palencia, L., Josse, V.
New Journal of Physics, 21, pages: 105002, IOP Publishing and Deutsche Physikalische Gesellschaft, October 2019 (article)
Elastic Scattering Time of Matter-Waves in Disordered Potentials
Richard, J., Lim, L., Denechaud, V., Volchkov, V., Lecoutre, B., Mukhtar, M., Jendrzejewski, F., Aspect, A., Signoles, A., Sanchez-Palencia, L., Josse, V.
Physical Review Letters, 122, pages: 100403, American Physical Society (APS), March 2019 (article)
We report on an extensive study of the elastic scattering time $τ_\mathrm{s}$ of matter waves in optical disordered potentials. Using direct experimental measurements, numerical simulations, and comparison with the first-order Born approximation based on the knowledge of the disorder properties, we explore the behavior of $τ_\mathrm{s}$ over more than 3 orders of magnitude, ranging from the weak to the strong scattering regime. We study in detail the location of the crossover and, as a main result, we reveal the strong influence of the disorder statistics, especially on the relevance of the widely used Ioffe-Regel-like criterion $k l_\mathrm{s}\sim 1$. While it is found to be relevant for Gaussian-distributed disordered potentials, we observe significant deviations for laser speckle disorders that are commonly used with ultracold atoms. Our results are crucial for connecting experimental investigation of complex transport phenomena, such as Anderson localization, to microscopic theories.
2018
Little Geodetic Evidence for Localized Indian Subduction in the Pamir-Hindu Kush of Central Asia
Perry, M., Kakar, N., Ischuk, A., Metzger, S., Bendick, R., Molnar, P., Mohadjer, S.
Geophysical Research Letters, 46(1):109-118, 2018 (article)
Measurement of Spectral Functions of Ultracold Atoms in Disordered Potentials
Volchkov, V., Pasek, M., Denechaud, V., Mukhtar, M., Aspect, A., Delande, D., Josse, V.
Physical Review Letters, 120, pages: 060404, American Physical Society (APS), January 2018 (article)
We report on the measurement of the spectral functions of noninteracting ultracold atoms in a three-dimensional disordered potential resulting from an optical speckle field. Varying the disorder strength by 2 orders of magnitude, we observe the crossover from the “quantum” perturbative regime of low disorder to the “classical” regime at higher disorder strength, and find an excellent agreement with numerical simulations. The method relies on the use of state-dependent disorder and the controlled transfer of atoms to create well-defined energy states. This opens new avenues for experimental investigations of three-dimensional Anderson localization.
Automatic Estimation of Modulation Transfer Functions
IEEE International Conference on Computational Photography (ICCP), pages: 1-12, May 2018 (conference)
2017
Review of GPS and Quaternary fault slip rates in the Himalaya-Tibet orogen
Mohadjer, S. E. T. A. B. R., Mutz, S. G.
Earth-Science Reviews , 174(174):39-52, 2017 (article)
Seismic monitoring of small alpine rockfalls – validity, precision and limitations
Dietze, M., Mohadjer, S., Turowski, J. M., Ehlers, T. A., Hovius, N.
Earth Surface Dynamics , 5(4):653–668, 2017 (article)
2016
A Quaternary fault database for central Asia
Mohadjer, S. E. T. A. B. R. S. K., Strube, T. A.
Natural Hazards and Earth System Sciences, 16(16):529-542, 2016 (article)
2015
Suppression and Revival of Weak Localization through Control of Time-Reversal Symmetry
Müller, K., Richard, J., Volchkov, V., Denechaud, V., Bouyer, P., Aspect, A., Josse, V.
Physical Review Letters, 114, pages: 205301, American Physical Society (APS), May 2015 (article)
We report on the observation of suppression and revival of coherent backscattering of ultracold atoms launched in an optical disorder in a quasi-2D geometry and submitted to a short dephasing pulse, as proposed by Micklitz, Müller, and Altland [Phys. Rev. B 91, 064203 (2015)]. This observation demonstrates a novel and general method to study weak localization by manipulating time reversal symmetry in disordered systems. In future experiments, this scheme could be extended to investigate higher order localization processes at the heart of Anderson (strong) localization.
2014
Efficient demagnetization cooling of atoms and its limits
Volchkov, V., Rührig, J., Pfau, T., Griesmaier, A.
Physical Review A, 89, pages: 043417, American Physical Society (APS), April 2014 (article)
Demagnetization cooling relies on spin-orbit coupling that brings motional and spin degrees of freedom into thermal equilibrium. In the case of a gas, one has the advantage that the spin degree of freedom can be cooled very efficiently using optical pumping. We investigate demagnetization cooling of a chromium gas in a deep optical dipole trap over a large temperature range and reach high densities up to 5×10^19 m^−3. We study the loss mechanism under such extreme conditions and identify excited-state collisions as the main limiting process. We discuss that in some systems demagnetization cooling has a realistic potential of reaching degeneracy by optical cooling only.
2013
Sisyphus cooling in a continuously loaded trap
Volchkov, V., Rührig, J., Pfau, T., Griesmaier, A.
New Journal of Physics, 15, pages: 093012, IOP Publishing and Deutsche Physikalische Gesellschaft, September 2013 (article)
We demonstrate continuous Sisyphus cooling combined with a continuous loading mechanism used to efficiently slow down and accumulate chromium atoms from a guided beam. While the loading itself is based on a single slowing step, applying a radio frequency field forces the atoms to repeat this step many times resulting in a so-called Sisyphus cooling. This extension allows efficient loading and cooling of atoms from a wide range of initial beam conditions. We study the interplay of the continuous loading and simultaneous Sisyphus cooling in different density regimes. In the case of a low density flux we observe a differential gain in phase-space density of nine orders of magnitude. This makes the presented scheme an ideal tool for reaching collisional densities enabling evaporative cooling—in spite of unfavourable initial conditions.
2012
Evaporation-limited loading of an atomic trap
Falkenau, M., Volchkov, V., Rührig, J., Gorniaczyk, H., Griesmaier, A.
Physical Review A, 85, pages: 023412, American Physical Society (APS), February 2012 (article)
Recently, we have experimentally demonstrated a continuous loading mechanism for an optical dipole trap from a guided atomic beam [M. Falkenau, V. V. Volchkov, J. Rührig, A. Griesmaier, and T. Pfau, Phys. Rev. Lett. 106, 163002 (2011)]. The observed evolution of the number of atoms and temperature in the trap are consequences of the unusual trap geometry. In the present paper, we develop a model based on a set of rate equations to describe the loading dynamics of such a mechanism. We consider the collision statistics in the nonuniform trap potential that leads to two-dimensional evaporation. The comparison between the resulting computations and experimental data allows to identify the dominant loss process and suggests ways to enhance the achievable steady-state atom number. Concerning subsequent evaporative cooling, we find that the possibility of controlling axial and radial confinement independently allows faster evaporation ramps compared to single beam optical dipole traps.
2011
Continuous Loading of a Conservative Potential Trap from an Atomic Beam
Falkenau, M., Volchkov, V., Rührig, J., Griesmaier, A., Pfau, T.
Physical Review Letters, 106, pages: 163002, American Physical Society (APS), April 2011 (article)
We demonstrate the fast accumulation of 52Cr atoms in a conservative potential from a guided atomic beam. Without laser cooling on a cycling transition, a dissipative step involving optical pumping allows us to load atoms at a rate of 2×10^7 s^−1 in the trap. Within less than 100 ms we reach the collisionally dense regime, from which we produce a Bose-Einstein condensate with subsequent evaporative cooling. This constitutes a new approach to degeneracy where Bose-Einstein condensation can be reached without a closed cycling transition, provided that a slow beam of particles can be produced.
2010
Laser cooling of a magnetically guided ultracold atom beam
Aghajani-Talesh, A., Falkenau, M., Volchkov, V., Trafford, L., Griesmaier, A., Pfau, T.
New Journal of Physics, 12, pages: 065018, IOP Publishing and Deutsche Physikalische Gesellschaft, June 2010 (article)
We report on the transverse laser cooling of a magnetically guided beam of ultracold chromium atoms. Radial compression by a tapering of the guide is employed to adiabatically heat the beam. Inside the tapered section, heat is extracted from the atom beam by a two-dimensional (2D) optical molasses perpendicular to it, resulting in a significant increase in atomic phase space density. A magnetic offset field is applied to prevent optical pumping to untrapped states. Our results demonstrate that, by a suitable choice of the magnetic offset field, the cooling beam intensity and detuning, atom losses and longitudinal heating can be avoided. Final temperatures below 65 μK have been achieved, corresponding to an increase in phase space density in the guided beam by more than a factor of 30.