Optical manipulation for studies of collisional dynamics of micron-sized droplets under gravity

Ivanov, Maksym; Chang, Kelken; Galinskiy, Ivan; Mehlig, B.; Hanstorp, Dag

doi:10.1364/oe.25.001391

Cited by 9 publications

(4 citation statements)

References 25 publications

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“…The experimental system presented here for educational purposes is also used in various research projects. For instance, the set-up has been used to study the collision of micrometersized droplets using high-speed cameras [18]. Further, the same experimental platform has been employed to construct a sensitive way to track the position of particles using a Sagnac interferometer [19].…”

Section: Discussionmentioning

confidence: 99%

A remote laboratory for optical levitation of charged droplets

et al. 2018

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We present a remotely controlled experiment in which liquid droplets are levitated by a vertically aligned focused laser beam. The droplets levitate at the point where the photon pressure of the focused laser beam balances the gravitational force. The size of a trapped droplet can be measured by detecting the diffraction pattern created by the trapping laser light. The charge on the trapped droplet can thereafter be determined by observing its motion when a vertically directed electrical field is applied. This experiment allows a student to study many fundamental physics processes, such as photon pressure, diffraction of light, or the motion of charged particles in electrical fields. The complexity of the experiments and the concept studied make this suitable for advanced studies in physics. The laser power required in the experiment is about 1 W, which is a thousand times greater than the value of 1 mW at which lasers begin to be capable of causing harm to eyes; high voltages are also used. Further, the cost of the equipment is relatively high, which limits its availability to most undergraduate teaching laboratories. It thus constitutes an ideal experiment for remote control.

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Section: Discussionmentioning

confidence: 99%

A remote laboratory for optical levitation of charged droplets

et al. 2018

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“…We analyzed data described in [29] and [30], and studied interactions between 186 pairs of water droplets settling past each other in still air as illustrated in Fig. 1.…”

Section: Methodsmentioning

confidence: 99%

Relative accelerations characterize the hydrodynamic interaction of cloud droplets

Kearney¹,

Bewley²

2022

Preprint

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Water droplets coalesce into larger ones in atmospheric clouds to form rain. But droplets on collision courses do not always coalesce due to the cushioning effects of the air between them. The extent to which these so-called hydrodynamic interactions reduce coalescence rates is embodied in the collision efficiency, which is often small and is not generally known. In order to characterize the mechanisms that determine the collision efficiency, we exploited new time-resolved three-dimensional droplet tracking techniques to measure the positions of cloud droplet pairs settling through quiescent air. We did so with an unprecedented precision that enabled us to calculate the relative positions, velocities, and accelerations of the droplets at droplet surface-to-surface separations as small as about one-tenth of a droplet diameter. We show that relative accelerations clearly distinguish coalescing from non-coalescing droplet trajectories, the former being associated with relative accelerations that exceeded a threshold value. We outline how relative accelerations relate to hydrodynamic interactions, and present scaling arguments that predict the threshold relative acceleration. We speculate that the relative acceleration distribution of droplets in turbulent clouds can parameterize the collision efficiency, and that this distribution together with the well-known relative position and velocity distributions can generate a physical description of both the collision and coalescence rates of cloud droplets. I. INTRODUCTIONIn warm atmospheric clouds, liquid water droplets are set onto collision courses by mechanisms that include differential sedimentation and turbulence [1][2][3]. The rate at which this happens can be explained by the way turbulence generates droplet relative position and velocity distributions [4,5]. In order for droplets on collision courses to coalescence into one larger droplet, however, they need to squeeze out the air between them, a process that couples the motions of droplets relative to one another through hydrodynamic interaction (HI) [e.g. 6, 7]. These interactions cause droplets to decelerate, which modifies the probability distributions of droplet relative positions and velocities in a way as yet unknown [e.g. 8-10]. The effect is most pronounced precisely where these distributions need to be evaluated, which is at the moment of contact between two droplets.Theoretical and empirical descriptions of the relative velocity distributions [e.g. 11-13] and radial distribution functions [e.g. 14-16] exist for droplets that are separated widely enough that they do not

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“…A double-beam trap is usually formed by two independent beams obtained using beam splitting optics, which requires precise positioning of the beams in the (xY y)-plane, but, in turn, complicates the optical scheme and alignment procedure [168]. This requirement is particularly relevant for traps that allow transporting particles over distances significantly exceeding the particle size, up to a few ten centimeters [165].…”

Section: Double-beam Trapsmentioning

confidence: 99%

“…Moreover, the range of axial particle displacement was limited by the depth of controlled overlap of the beams and was from 20 to 100 mm, which also provided a possibility of trapping an ensemble of a few particles. Later on, A Kalume [170,171] demonstrated the control of the axial position of liquid microscopic droplets with a diameter of 20±25 mm in air using a similar scheme and hollow beams [168].…”

Section: Double-beam Trapsmentioning

confidence: 99%

Optical tweezers and manipulators. Modern concepts and future prospect

2022

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The review aims to generalize fundamental concepts that are necessary for understanding the mechanisms and principles of optical trapping in both liquid media and air. One of the objectives of the article is to familiarize a wide audience with the global experience and the prospects for developing the fundamental principles of the functioning of optical tweezers for various purposes. The paper describes in detail the design options of optical manipulators in terms of versatility and energy efficiency of their use in a wide range of modern practical purposes and tasks.

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Optical manipulation for studies of collisional dynamics of micron-sized droplets under gravity

Cited by 9 publications

References 25 publications

A remote laboratory for optical levitation of charged droplets

A remote laboratory for optical levitation of charged droplets

Relative accelerations characterize the hydrodynamic interaction of cloud droplets

Optical tweezers and manipulators. Modern concepts and future prospect

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