| 1. |
- Schmidt, Falko, 1992, et al.
(author)
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Non-equilibrium properties of an active nanoparticle in a harmonic potential
- 2021
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In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723 .- 2041-1723. ; 11926
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Journal article (peer-reviewed)abstract
- Active particles break out of thermodynamic equilibrium thanks to their directed motion, which leads to complex and interesting behaviors in the presence of confining potentials. When dealing with active nanoparticles, however, the overwhelming presence of rotational diffusion hinders directed motion, leading to an increase of their effective temperature, but otherwise masking the effects of self-propulsion. Here, we demonstrate an experimental system where an active nanoparticle immersed in a critical solution and held in an optical harmonic potential features far-from-equilibrium behavior beyond an increase of its effective temperature. When increasing the laser power, we observe a cross-over from a Boltzmann distribution to a non-equilibrium state, where the particle performs fast orbital rotations about the beam axis. These findings are rationalized by solving the Fokker-Planck equation for the particle’s position and orientation in terms of a moment expansion. The proposed self-propulsion mechanism results from the particle’s non-sphericity and the lower critical point of the solution.
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| 2. |
- Tello Marmolejo, Javier, 1995, et al.
(author)
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A water droplet as a toy atom
- 2022
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In: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 12198
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Conference paper (peer-reviewed)abstract
- Common atomic physics courses jump from the square and harmonic well potentials straight to the hydrogen atom. However, there is a missing link in between, the spherical well potential. Although it is included in some textbooks, the lack of an experimental backing means the problem quickly becomes mathematically complex. Here we have built an optical toy atom using the scattering of an optically levitated, evaporating water droplet. We find a greatly simplified Mie scattering spectrum composed of a series of evolving Fano resonances organized in a set of combs. The whole spectrum can be intuitively explained through an analogy to a quantum spherical well potential. This produces a model of an atom including ground and excited states, quantized angular momentum, and tunneling.
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| 3. |
- Arran, C., et al.
(author)
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Potential to measure quantum effects in recent all-optical radiation reaction experiments
- 2019
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In: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 11039
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Conference paper (peer-reviewed)abstract
- The construction of 10 PW class laser facilities with unprecedented intensities has emphasized the need for a thorough understanding of the radiation reaction process. We describe simulations for a recent all-optical colliding pulse experiment, where a GeV scale electron bunch produced by a laser wakefield accelerator interacted with a counter-propagating laser pulse. In the rest frame of the electron bunch, the electric field of the laser pulse is increased by several orders of magnitude, approaching the Schwinger field and leading to substantial variation from the classical Landau-Lifshitz model. Our simulations show how the final electron and photon spectra may allow us to differentiate between stochastic and semi-classical models of radiation reaction, even when there is significant shot-to-shot variation in the experimental parameters. In particular, constraints are placed on the maximum energy spread and shot-to-shot variation permissible if a stochastic model is to be proven with confidence.
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| 4. |
- Fusco, Zelio, et al.
(author)
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Hybrid plasmonic-semiconducting fractal metamaterials for superior sensing of volatile compounds
- 2019
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In: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 11202
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Conference paper (peer-reviewed)abstract
- Localized surface plasmon resonance (LSPR) is a subwavelength optical phenomenon that has found widespread use in bio-and chemical-sensing applications thanks to the possibility to efficiently transduce refractive index changes into wavelength shifts. However, is it very hard to transpose the successes demonstrated in liquid and physiological environment toward the detection of gasous molecules. In fact, the latter typically adsorb in an unspecific manner and induce very minute refractive index changes tipicaly below the sensor sensitivity. Here, we show first insights on the aerosol large-scale self-Assembly of metasurfaces made of monocrystalline Au nanoislands with uniform disorder over large scale. Notably, these architectures show tuneable disorder levels and demonstrate high-quality LSPR, enabling the fabrication of highly performing optical gas sensors detecting down to 10-5 variations in refractive index. Next, we use our aerosol synthesis method to integrate tailored fractals of dielectric TiO2 nanoparticles onto resonant plasmonic metasurfaces. We show how this integration strongly enhances the interaction between the plasmonic field and volatile organic molecules and provides a means for their selective detection. Interesting, the improved performance is the result of a synergetic behavior between the dielectric fractals and the plasmonic metasurface: in fact, upon this integration, the enhancement of plasmonic field is drastically extended, all the way up to a maximum thickness of 1.8 μm. Optimal dielectric-plasmonic structures allow measurements of changes in the refractive index of the gas mixture down to <8x10-6at room temperature and selective identification of three exemplary volatile organic compounds (VOCs). These findings provide a basis for the development of a novel family of hybrid dielectric-plasmonic materials with application extending from light harvesting and photo-catalysts to contactless sensors for non-invasive medical diagnostics.
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| 5. |
- Lindgren, Erik, 1980, et al.
(author)
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Analysis of industrial X-ray computed tomography data with deep neural networks
- 2021
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In: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. ; 11840
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Conference paper (peer-reviewed)abstract
- X-ray computed tomography (XCT) is increasingly utilized industrially at material- and process development as well as in non-destructive quality control; XCT is important to many emerging manufacturing technologies, for example metal additive manufacturing. These trends lead to increased needs of safe automatic or semi-automatic data interpretation, considered an open research question for many critical high value industrial products such as within the aerospace industry. By safe, we mean that the interpretation is not allowed to unawarely or unexpectedly fail; specifically the algorithms must react sensibly to inputs dissimilar to the training data, so called out-of-distribution (OOD) inputs. In this work we explore data interpretation with deep neural networks to address: robust safe data interpretation which includes a confidence estimate with respect to OOD data, an OOD detector; generation of realistic synthetic material aw indications for the material science and nondestructive evaluation community. We have focused on industrial XCT related challenges, addressing difficulties with spatially correlated X-ray quantum noise. Results are reported on training auto-encoders (AE) and generative adversarial networks (GAN), on a publicly available XCT dataset of additively manufactured metal. We demonstrate that adding modeled X-ray noise during training reduces artefacts in the generated imperfection indications as well as improves the OOD detector performance. In addition, we show that the OOD detector can detect real and synthetic OOD data and still model the accepted in-distribution data down to the X-ray noise levels.
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| 6. |
- Lindgren, Erik, et al.
(author)
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Deep-learning-based out-of distribution data detection in visual inspection images
- 2023
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In: Proceedings Of Spie 12489, NDE 4.0, Predictive Maintenance, Communication, and Energy Systems. - : Spie Digital Library. ; 12489
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Conference paper (peer-reviewed)abstract
- Within quality critical industries, e.g. aerospace, quality control with non-destructive evaluation (NDE) is essential. The surface quality is often important and e.g. visual inspection is often applied. Part of the inspection is the data interpretation, not easily made automatic for critical products. Recent studies on the automatization have indicated promising results utilizing deep-learning-based artificial intelligence. However, many such algorithms are known to be overconfident when subjected to unexpected input (e.g. new/rare material defects) far from the training dataset, so-called out-of-distribution (OOD) data. We claim that safe computer-based interpretation of NDE data within quality critical applications, must respond sensible also to OOD data. A sensible response could be that the algorithms identify such OOD data and forward it to a human for further analysis. Such an OOD detector could facilitate a human-machine collaboration in a NDE 4.0 vision. In this work we have explored if a recently proposed (for industrial x-ray images) auto-encoder-based approach can be utilized as OOD detector (one-class classifier) for visual inspection data. The model is trained in an unsupervised manner on accepted input to reconstruct it at high precision. Simultaneously it is trained to remove synthetically added defect indications to generate a clean image patch, similar to denoising-auto-enoders. The difference between the input and reconstructed input is analyzed for OOD detection. We train and test the algorithm on a publicly available visual inspection dataset with surface defects. We achieve true positive rates at 0.90 with true negative rates at 0.99 and demonstrate detection of OOD data.
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| 7. |
- Löfstrand, Anette, et al.
(author)
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Sequential infiltration synthesis and pattern transfer using 6 nm half-pitch carbohydrate-based fingerprint block copolymer
- 2021
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In: Advances in Patterning Materials and Processes XXXVIII. - : SPIE. - 0277-786X .- 1996-756X. - 9781510640573 - 9781510640580 ; 11612
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Conference paper (peer-reviewed)abstract
- This study presents how sequential infiltration synthesis of trimethyl aluminium and water into a carbohydrate-based block copolymer was used to enable pattern transfer of 6 nm half-pitch horizontal cylinders into silicon. Specular neutron reflectometry measurements of poly(styrene)-block-maltoheptaose self-assembled into horizontal cylinders indicate an increasing content of alumina after each sequential infiltration cycle, comparing 0, 1, 2, and 4 cycles, with alumina content reaching 2.4 vol% after four infiltrations cycles. Dry etching processes in inductively coupled plasma reactive ion etching for sub-10 nm patterns were developed, using a two-step technique: O2-plasma for polymer removal and a reactive ion etching of Si using a mixture of SF6 and C4F8 gases. Etch selectivity of more than 2:1 of silicon over alumina-like etch mask material was achieved. To evaluate the etching process, the etched Si structures were measured and characterized by scanning electron microscopy. These results are expected to be of use for nanofabrication and applications in the sub-10 nm regime.
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| 8. |
- Vaičaitis, Virgilijus, et al.
(author)
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Generation of broadband THz beams with azimuthally modulated phase and intensity by femtosecond laser pulses in air plasma
- 2019
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In: Proceedings of SPIE - The International Society for Optical Engineering. - 0277-786X .- 1996-756X. ; 11370, s. 443-444
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Conference paper (peer-reviewed)abstract
- We report efficient generation of the broadband terahertz (THz) radiation by bichromatic femtosecond laser pulses with flat phase fronts or with a phase singularity focused in air. As a pump source, the fundamental and second harmonic radiations of a femtosecond Ti:sapphire laser were used. While the fundamental laser beam had Gaussian intensity distribution and a flat phase front, the second harmonic beam had either flat or helical phase front forming an optical vortex. In both cases the angular spectra of THz radiation and azimuthal phase distributions of THz beams were investigated. It was found that when both the fundamental and second harmonic laser pulses had Gaussian profiles, the resulting THz radiation was generated as an axially symmetric cone with a flat phase front. However, when the Gaussian second harmonic beam was replaced by the one with optical singularity, the intensity and the phase of generated THz cone became modulated along the azimuthal angle. The spectrum of generated THz pulses spanned up to 50 THz in both cases. Our theoretical analysis based on the photocurrent model was in good agreement with the experimental data.
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| 9. |
- Giono, G., et al.
(author)
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Characterisation of the analogue read-out chain for the CCDs onboard the mesospheric airglow/aerosol tomography and spectroscopy (MATS)
- 2018
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In: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9781510619494 ; 10698
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Conference paper (peer-reviewed)abstract
- The MATS satellite aims at observing airglow and noctilucent clouds in the mesosphere. The main instrument consists of a six channels limb imager in the near-ultraviolet and near-infrared. A high signal-to-noise ratio is required for detecting these mesospheric phenomena: 100 and 500 for ultraviolet and infrared, respectively. This is achieved by an optical design minimizing stray-light, but also with a dedicated design of the read-out analogue chain for the CCD on each channel. The requirements and expected light level on the imaging channels are brie y discussed before focusing on the CCD read-out analogue chain, for which the design and performances are presented.
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| 10. |
- Harvey, Christopher, 1982, et al.
(author)
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High-energy gamma-ray beams from nonlinear Thomson and Compton scattering in the ultra-intense regime
- 2015
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In: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9781628416305 ; 9509, s. 950908-
-
Conference paper (peer-reviewed)abstract
- We consider the Thomson and Compton scattering of high-energy electrons in an intense laser pulse. Our simulations show that energy losses due to radiation reaction cause the emitted radiation to be spread over a broader angular range than the case without these losses included. We explain this in terms of the effect of these energy losses on the particle dynamics. Finally, at ultra-high intensities, i.e. fields with a dimensionless parameter a(0)similar to 200, the energy of the emission spectrum is significantly reduced by radiation reaction and also the classical and QED results begin to differ. This is found to be due to the classical theory overestimating the energy loss of the electrons. Such findings are relevant to radiation source development involving the next generation of high-intensity laser facilities.
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