| 1. |
- Bronte Ciriza, David, et al.
(författare)
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Faster and More Accurate Geometrical-Optics Optical Force Calculation Using Neural Networks
- 2022
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Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 10:1, s. 234-41
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Tidskriftsartikel (refereegranskat)abstract
- Optical forces are often calculated by discretizing the trapping light beam into a set of rays and using geometrical optics to compute the exchange of momentum. However, the number of rays sets a trade-off between calculation speed and accuracy. Here, we show that using neural networks permits overcoming this limitation, obtaining not only faster but also more accurate simulations. We demonstrate this using an optically trapped spherical particle for which we obtain an analytical solution to use as ground truth. Then, we take advantage of the acceleration provided by neural networks to study the dynamics of ellipsoidal particles in a double trap, which would be computationally impossible otherwise.
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| 2. |
- Bronte Ciriza, David, et al.
(författare)
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Optically Driven Janus Microengine with Full Orbital Motion Control
- 2023
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Ingår i: ACS PHOTONICS. - 2330-4022. ; 10:9, s. 3223-3232
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Tidskriftsartikel (refereegranskat)abstract
- Microengines have shown promise for a variety of applications in nanotechnology, microfluidics, and nanomedicine, including targeted drug delivery, microscale pumping, and environmental remediation. However, achieving precise control over their dynamics remains a significant challenge. In this study, we introduce a microengine that exploits both optical and thermal effects to achieve a high degree of controllability. We find that in the presence of a strongly focused light beam, a gold-silica Janus particle becomes confined at the stationary point where the optical and thermal forces balance. By using circularly polarized light, we can transfer angular momentum to the particle, breaking the symmetry between the two forces and resulting in a tangential force that drives directed orbital motion. We can simultaneously control the velocity and direction of rotation of the particle changing the ellipticity of the incoming light beam while tuning the radius of the orbit with laser power. Our experimental results are validated using a geometrical optics phenomenological model that considers the optical force, the absorption of optical power, and the resulting heating of the particle. The demonstrated enhanced flexibility in the control of microengines opens up new possibilities for their utilization in a wide range of applications, including microscale transport, sensing, and actuation.
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| 3. |
- Callegari, Agnese, et al.
(författare)
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Optical trapping and critical Casimir forces
- 2021
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Ingår i: European Physical Journal Plus. - : Springer Science and Business Media LLC. - 2190-5444. ; 136:2
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Tidskriftsartikel (refereegranskat)abstract
- Critical Casimir forces emerge between objects, such as colloidal particles, whenever their surfaces spatially confine the fluctuations of the order parameter of a critical liquid used as a solvent. These forces act at short but microscopically large distances between these objects, reaching often hundreds of nanometers. Keeping colloids at such distances is a major experimental challenge, which can be addressed by the means of optical tweezers. Here, we review how optical tweezers have been successfully used to quantitatively study critical Casimir forces acting on particles in suspensions. As we will see, the use of optical tweezers to experimentally study critical Casimir forces can play a crucial role in developing nano-technologies, representing an innovative way to realize self-assembled devices at the nano- and microscale.
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| 4. |
- Callegari, Agnese, et al.
(författare)
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Optical Trapping and Critical Casimir Forces
- 2023
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. - 0277-786X .- 1996-756X. - 9781510663398
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Konferensbidrag (refereegranskat)abstract
- Critical Casimir forces emerge between objects, such as colloidal particles, whenever their surfaces spatially confine the fluctuations of the order parameter of a critical liquid used as a solvent. These forces act at short but microscopically large distances between these objects, often reaching hundreds of nanometers. Keeping colloids at such distances is a major experimental challenge, which can be addressed by the means of optical tweezers. Here, we review how optical tweezers have been successfully used to quantitatively study critical Casimir forces acting on particles in suspensions. As we will see, the use of optical tweezers to experimentally study critical Casimir forces can play a crucial role in developing nanotechnologies, representing an innovative way to realize self-assembled devices at the nano- and microscale.
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| 5. |
- Callegari, Agnese, et al.
(författare)
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Optical Trapping and Critical Casimir Forces
- 2023
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Ingår i: Optical Manipulation and Its Applications, OMA 2023. - 9781957171210
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Konferensbidrag (refereegranskat)abstract
- Critical Casimir forces between colloidal particles act at distances reaching often hundreds of nanometers. Keeping colloids at such distances is a major experimental challenge. Here, we review how optical tweezers help quantitatively in studying critical Casimir forces acting on particles in suspensions.
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| 6. |
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| 7. |
- Gieseler, J., et al.
(författare)
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Optical tweezers - from calibration to applications: a tutorial
- 2021
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Ingår i: Advances in Optics and Photonics. - : Optica Publishing Group. - 1943-8206. ; 13:1, s. 74-241
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Tidskriftsartikel (refereegranskat)abstract
- Since their invention in 1986 by Arthur Ashkin and colleagues, optical tweezers have become an essential tool in several fields of physics, spectroscopy, biology, nanotechnology, and thermodynamics. In this tutorial, we provide a primer on how to calibrate optical tweezers and how to use them for advanced applications. After a brief general introduction on optical tweezers, we focus on describing and comparing the various available calibration techniques. Then, we discuss some cutting-edge applications of optical tweezers in a liquid medium, namely, to study single-molecule and single-cell mechanics, microrheology, colloidal interactions, statistical physics, and transport phenomena. Finally, we consider optical tweezers in vacuum, where the absence of a viscous medium offers vastly different dynamics and presents new challenges. We conclude with some perspectives for the field and the future applications of optical tweezers. This tutorial provides both a step-by-step guide ideal for non-specialists entering the field and a comprehensive manual of advanced techniques useful for expert practitioners. All of the examples are complemented by the sample data and software necessary to reproduce them. (C) 2021 Optical Society of America.
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| 8. |
- Gillibert, R., et al.
(författare)
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Raman Tweezers for Small Microplastics and Nanoplastics Identification in Seawater
- 2019
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Ingår i: Environmental Science & Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 53:15, s. 9003-9013
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Tidskriftsartikel (refereegranskat)abstract
- Our understanding of the fate and distribution of micro- and nano- plastics in the marine environment is limited by the intrinsic difficulties of the techniques currently used for the detection, quantification, and chemical identification of small particles in liquid (light scattering, vibrational spectroscopies, and optical and electron microscopies). Here we introduce Raman Tweezers (RTs), namely optical tweezers combined with Raman spectroscopy, as an analytical tool for the study of micro- and nanoplastics in seawater. We show optical trapping and chemical identification of sub-20 mu m plastics, down to the 50 nm range. Analysis at the single particle level allows us to unambiguously discriminate plastics from organic matter and mineral sediments, overcoming the capacities of standard Raman spectroscopy in liquid, intrinsically limited to ensemble measurements. Being a microscopy technique, RTs also permits one to assess the size and shapes of particles (beads, fragments, and fibers), with spatial resolution only limited by diffraction. Applications are shown on both model particles and naturally aged environmental samples, made of common plastic pollutants, including polyethylene, polypropylene, nylon, and polystyrene, also in the presence of a thin ecocorona. Coupled to suitable extraction and concentration protocols, RTs have the potential to strongly impact future research on micro and nanoplastics environmental pollution, and enable the understanding of the fragmentation processes on a multiscale level of aged polymers.
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| 9. |
- Magazzu, Alessandro, et al.
(författare)
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Controlling the dynamics of colloidal particles by critical Casimir forces
- 2019
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 15:10, s. 2152-2162
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Tidskriftsartikel (refereegranskat)abstract
- © 2019 The Royal Society of Chemistry. Critical Casimir forces can play an important role for applications in nano-science and nano-technology, owing to their piconewton strength, nanometric action range, fine tunability as a function of temperature, and exquisite dependence on the surface properties of the involved objects. Here, we investigate the effects of critical Casimir forces on the free dynamics of a pair of colloidal particles dispersed in the bulk of a near-critical binary liquid solvent, using blinking optical tweezers. In particular, we measure the time evolution of the distance between the two colloids to determine their relative diffusion and drift velocity. Furthermore, we show how critical Casimir forces change the dynamic properties of this two-colloid system by studying the temperature dependence of the distribution of the so-called first-passage time, i.e., of the time necessary for the particles to reach for the first time a certain separation, starting from an initially assigned one. These data are in good agreement with theoretical results obtained from Monte Carlo simulations and Langevin dynamics.
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| 10. |
- Neves, Antonio Alvaro Ranha, et al.
(författare)
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Beam displacement due to thermal blooming in optical tweezers
- 2019
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Ingår i: Optical Manipulation and Its Applications - Proceedings Biophotonics Congress: Optics in the Life Sciences Congress 2019 (BODA, BRAIN, NTM, OMA, OMP).
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Konferensbidrag (refereegranskat)abstract
- Water near an optically trapped particle absorbs part of the laser energy resulting in changes for the refractive index and density. Particle position and optical potential description are affected by this photothermal effect.
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