185 research outputs found

    Levitated optomechanics: A tutorial and perspective

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    Optomechanics, the study of the mechanical interaction of light with matter, has proven to be a fruitful area of research that has yielded many notable achievements, including the direct detection of gravitational waves in kilometer-scale optical interferometers. Light has been used to cool and demonstrate quantum control over the mechanical degrees of freedom of individual ions and atoms, and more recently has facilitated the observation of quantum ``mechanics'' in objects of larger mass, even at the kg-scale. Levitated optomechanics, where an object can be suspended by radiation pressure and largely decoupled from its environment, has recently established itself as a rich field of study, with many notable results relevant for precision measurement, quantum information science, and foundational tests of quantum mechanics and fundamental physics. This article provides a survey of several current activities in field along with a tutorial describing associated key concepts and methods, both from an experimental and theoretical approach. It is intended as a resource for junior researchers who are new to this growing field as well as beginning graduate students. The tutorial is concluded with a perspective on both promising emerging experimental platforms and anticipated future theoretical developments.Comment: 50 pages, 19 figures, submitted to Advances in Optics and Photonic

    Exploring communication and collective behaviour between spatially organised inorganic protocell communities

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    A living system profoundly relies on mass, information and energy interactions through cell-cell and cell-environment networks. As a step towards understanding such interactions, it is beneficial to design and create bottom-up artificial living systems from non-living components, with a specific focus on synergistic interactivity between artificial cells (protocells) and their local environment. Although there are several routes for fabricating protocellular systems, we recognise key challenges associated with a) developing protocellular models with high levels of organisational tunability, b) achieving cell-environment bilateral communication, and c) realising autonomous self-assembly and regulation of protocell systems. The aim of this thesis is thus to review some matrix-based and matrix-free methods of inorganic protocell (colloidosome) 3D-spatial organisation, as judicious system designs capable of cell-cell and cell-environment communication, collective behaviours, and dynamic self-assembly, in close relation with local environments.The first experimental chapter details assembly of colloidosomes within hydrogel or coacervate-based matrices. A droplet microfluidic technique is employed as a novel method for encapsulating segregated colloidosome colonies within alginate hydrogel microspheres. The technique exploits high tunability for customisable size, ratio, microscale geometry, and 3D-patterning parameters. Benefiting from the versatility associated with such matrix-based systems, the second experimental chapter develops 3D-organised colloidosomes for collective signalling and emergent behaviours. Notably, spatially segregated colonies show proximity-mediated chemical communication with increased kinetics compared to analogous homogenous arrangements. This proximity-enhanced colloidosome signalling is exploited, alongside segregated ionic/covalent crosslinking transitions in the environment, to obtain simultaneous structural degradation and resilience of hydrogel hemispheres as a programmable mechanism for protocell ejection. Colloidosomes are also employed as simple signalling hotspots within coacervate-matrix systems. The final experimental chapter aims to re-imagine colloidosome organisation into a matrix-free system, capable of dynamic self-assembly and self-sorting via electrostatically-active membrane appendages. Alginate-coated and chitosan-coated colloidosomes are either co-assembled or self-sorted, in response to varied pH environments. Again, these systems are highly coordinated with their environment and as such, can be spatially pattered according to temporal pH changes through endogenous enzyme catalysis. Furthermore, a spatiotemporal effect on the rate of colloidosome communication in the presence of a hostile guest molecule is demonstrated. <br/

    Single-molecule Characterisation of DNA Hybridization via Fluorescence Microscopy and Optoplasmonic Sensing Approaches

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    The single-molecule study provides an unprecedented deep view into the biological process, unveiling the hidden heterogeneity that is hard to observe in ensemble methods. Recently, various techniques have shown the detection of biomolecules with single-molecule level sensitivity. However, each technique has its unique advantages and drawbacks. Single-molecule techniques can influence the molecular systems that they intend to detect in different ways. For example, fluorescence labels may affect the kinetics and dynamics of biomolecular interactions, while plasmonic-based approaches use local field enhancements that are not uniform across the involved plasmonic nanostructures, both of which can play a significant role in the observed statistics. Before one can combine the information obtained from fluorescence and optoplasmonic techniques, single-molecule experiments must be compared and cross-validated. Here we first compare the detection of DNA hybridization on fluorescence-based imaging technique and optoplasmionic sensors. We investigate the impact of (i) the presence of labels, and (ii) the potential influence of the plasmonic nanoparticle surface. Our measurements reveal that the dissociation rates of hybridized DNA strands are approximately the same for both techniques. Our study establishes the equivalence of both techniques for this DNA molecular test system and can serve as the basis for combining these techniques in other single-molecule studies. With optoplasmonic sensing, our results indicate that one may benefit from the larger binding efficiency of fluorescence imaging while the impact of the label is checked with the optoplasmonic sensing platform. To further combine the two single-molecule characterisation systems, we developed the first optical setup that integrates optoplasmonic and fluorescence-based detection. These sub-platforms provide complementary insights into single-molecule processes. We record the fluorescence and optoplasmonic sensor signals for individual, transient DNA hybridisation events. The hybridisation events are observed in the same sample cell and over a prolonged time (i.e. towards high binding site occupancies). A decrease in the association rate over the measurement duration is reported. Our dual optoplasmonic sensing and imaging platform offers insight into the observed phenomenon, revealing that irreversible hybridisation events accumulate over detected step signals in optoplasmonic sensing. Our results point to novel physicochemical mechanisms that result in the stabilisation of DNA hybridisation on optically-excited plasmonic nanoparticles.Operating Budge

    Measurements and simulations of thermoplasmonically induced Marangoni flows

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    Particle transport in microfluidic environments is often dominated by slow diffusion near interfaces. However, by inducing localized fluid flow, it is possible to actively transport suspended nano-objects in confined spaces. One promising method for achieving precise and dynamic control over fluid flow on the microscale is to use photothermal effects based on the illumination of plasmonic metal nanoparticles, which exhibit very high optical absorption for light wavelengths near resonance. The particles can thus be used as nanoscale heat sources that locally increase the temperature of the surrounding fluid, resulting in processes such as thermophoresis, convection, and vapor bubble generation. This thesis focuses on the latter effect and the associated bubble nucleation and thermal Marangoni convection processes.Marangoni flows result from the surface tension gradient that establishes on a thermoplasmonically induced vapor bubble at equilibrium. However, in addition to this, strong flow transients appear as a bubble is created and expands. Both phenomena lead to similar flow profiles. Here it is shown that the direction of these flows can be controlled by manipulating the temperature gradient on the surface of the bubble. Specifically, it is demonstrated that the direction of the strong transient flows around a nanobubble can be reverted by breaking the photothermal symmetry using two unequal nearby arrays of plasmonic nanoparticles. Furthermore, we investigate the possibility of remotely controlling the flow direction by turning the incident light polarization. The results are based on vectorial flow measurements using optical force microscopy supported by extensive flow profile simulations

    Roadmap for optical tweezers

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    Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiere, y los autores pertenecientes a la UAMOptical tweezers are tools made of light that enable contactless pushing, trapping, and manipulation of objects, ranging from atoms to space light sails. Since the pioneering work by Arthur Ashkin in the 1970s, optical tweezers have evolved into sophisticated instruments and have been employed in a broad range of applications in the life sciences, physics, and engineering. These include accurate force and torque measurement at the femtonewton level, microrheology of complex fluids, single micro- and nano-particle spectroscopy, single-cell analysis, and statistical-physics experiments. This roadmap provides insights into current investigations involving optical forces and optical tweezers from their theoretical foundations to designs and setups. It also offers perspectives for applications to a wide range of research fields, from biophysics to space explorationEuropean Commission (Horizon 2020, Project No. 812780

    Driven colloidal particles in optical potential energy landscapes

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    The structure and dynamics of colloidal particles in optical potential energy landscapes is studied. Experiments use paramagnetic or optically anisotropic colloidal particles interacting with lines or pairs of time-dependent optical traps. First, the pairwise interactions of the paramagnetic particles are measured using pairs of optical traps. We test a novel data analysis method under various conditions and calculate the magnetic susceptibility of the particles. Next, we measure the structure and dynamics of chains of paramagnetic colloids in a sinusoidal optical potential of varying depth. At well defined chain lengths, we observe a transition from an asymmetric, strongly pinned state to a free-sliding, symmetric state as the optical potential decreases. We then analyse the frictional dynamics of the same system under a constant driving force and observe a transition from low to high friction as the optical potential increases. We model the dynamics of the chains in the low and high friction regimes. The simple hard sphere model developed for the high friction regime is used to derive an equation which predicts the transition point from low to high friction. Next, we drive the chains through a time-dependent optical potential with an oscillating depth. We analyse the synchronisation of the chain’s motion to the oscillations of the potential and characterise the dynamics, observing a novel mode of motion involving the simultaneous nucleation of kinks and anti-kinks. Finally, we study the dynamics of a single optically anisotropic dumbbell particle interacting with a repulsive optical trap controlled by a time-delayed feedback protocol. We observe a transition from diffusive to driven dynamics which is modelled using delay-differential equations. We find that this transition coincides with the maximum work done on the particle and a local minimum in the mutual information between the particle and the trap

    Physics and applications of dusty plasmas: The Perspectives 2023

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    Dusty plasmas are electrically quasi-neutral media that, along with electrons, ions, neutral gas, radiation, and electric and/or magnetic fields, also contain solid or liquid particles with sizes ranging from a few nanometers to a few micrometers. These media can be found in many natural environments as well as in various laboratory setups and industrial applications. As a separate branch of plasma physics, the field of dusty plasma physics was born in the beginning of 1990s at the intersection of the interests of the communities investigating astrophysical and technological plasmas. An additional boost to the development of the field was given by the discovery of plasma crystals leading to a series of microgravity experiments of which the purpose was to investigate generic phenomena in condensed matter physics using strongly coupled complex (dusty) plasmas as model systems. Finally, the field has gained an increasing amount of attention due to its inevitable connection to the development of novel applications ranging from the synthesis of functional nanoparticles to nuclear fusion and from particle sensing and diagnostics to nano-contamination control. The purpose of the present perspectives paper is to identify promising new developments and research directions for the field. As such, dusty plasmas are considered in their entire variety: from classical low-pressure noble-gas dusty discharges to atmospheric pressure plasmas with aerosols and from rarefied astrophysical plasmas to dense plasmas in nuclear fusion devices. Both fundamental and application aspects are covered

    Roadmap for optical tweezers

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    Optical tweezers are tools made of light that enable contactless pushing, trapping, and manipulation of objects, ranging from atoms to space light sails. Since the pioneering work by Arthur Ashkin in the 1970s, optical tweezers have evolved into sophisticated instruments and have been employed in a broad range of applications in the life sciences, physics, and engineering. These include accurate force and torque measurement at the femtonewton level, microrheology of complex fluids, single micro- and nano-particle spectroscopy, single-cell analysis, and statistical-physics experiments. This roadmap provides insights into current investigations involving optical forces and optical tweezers from their theoretical foundations to designs and setups. It also offers perspectives for applications to a wide range of research fields, from biophysics to space exploration.journal articl
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