| 1. |
- Bae, A. J., et al.
(författare)
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Juggling with Light
- 2019
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Ingår i: Physical Review Letters. - 0031-9007. ; 122:4
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Tidskriftsartikel (refereegranskat)abstract
- We discovered that when a pair of small particles is optically levitated, the particles execute a "dance" whose motion resembles the orbits of balls being juggled. This motion lies in a plane perpendicular to the polarization of the incident light. We ascribe the dance to a mechanism by which the dominant force on each particle cyclically alternates between radiation pressure and gravity as each particle takes turns eclipsing the other. We explain the plane of motion by considering the anisotropic scattering of polarized light at a curved interface.
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| 2. |
- Hanstorp, Dag, 1960, et al.
(författare)
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A versatile system for optical manipulation experiments
- 2017
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Ingår i: Proceedings of SPIE - The International Society for Optical Engineering. SPIE Nanoscience + Engineering, 2017, San Diego, California, United States. - : SPIE. - 0277-786X .- 1996-756X. - 9781510611528
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Konferensbidrag (refereegranskat)abstract
- Downloading of the abstract is permitted for personal use only. In this paper a versatile experimental system for optical levitation is presented. Microscopic liquid droplets are produced on demand from piezo-electrically driven dispensers. The charge of the droplets is controlled by applying an electric field on the piezo-dispenser head. The dispenser releases droplets into a vertically focused laser beam. The size and position in 3 dimensions of trapped droplets are measured using two orthogonally placed high speed cameras. Alternatively, the vertical position is determined by imaging scattered light onto a position sensitive detector. The charge of a trapped droplets is determined by recording its motion when an electric field is applied, and the charge can be altered by exposing the droplet to a radioactive source or UV light. Further, spectroscopic information of the trapped droplet is obtained by imaging the droplet on the entrance slit of a spectrometer. Finally, the trapping cell can be evacuated, allowing investigations of droplet dynamics in vacuum. The system is utilized to study a variety of physical phenomena, and three pilot experiments are given in this paper. First, a system used to control and measure the charge of the droplet is presented. Second, it is demonstrated how particles can be made to rotate and spin by trapping them using optical vortices. Finally, the Raman spectra of trapped glycerol droplets are obtained and analyzed. The long term goal of this work is to create a system where interactions of droplets with the surrounding medium or with other droplets can be studied with full control of all physical variables.
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| 3. |
- Ivanov, Maksym, et al.
(författare)
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Optical manipulation for studies of collisional dynamics of micron-sized droplets under gravity
- 2017
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Ingår i: Optics Express. - 1094-4087. ; 25:2, s. 1391-1404
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Tidskriftsartikel (refereegranskat)abstract
- © 2017 Optical Society of America.A new experimental technique for creating and imaging collisions of micron-sized droplets settling under gravity is presented. A pair of glycerol droplets is suspended in air by means of two optical traps. The droplet relative velocities are determined by the droplet sizes. The impact parameter is precisely controlled by positioning the droplets using the two optical traps. The droplets are released by turning off the trapping light using electro-optical modulators. The motion of the sedimenting droplets is then captured by two synchronized high-speed cameras, at a frame rate of up to 63 kHz. The method allows the direct imaging of the collision of droplets without the influence of the optical confinement imposed by the trapping force. The method will facilitate efficient studies of the microphysics of neutral, as well as charged, liquid droplets and their interactions with light, electric field and thermodynamic environment, such as temperature or vapor concentration.
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| 4. |
- Ivanov, M., et al.
(författare)
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Spectroscopy and optical imaging of coalescing droplets
- 2016
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Ingår i: SPIE Proceedings, Volume 9922, Optical Manipulation of Matter in Vaccum or Through Gaseous Media.. - : SPIE. - 9781510602359
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Konferensbidrag (refereegranskat)abstract
- We report on experimental investigations of the dynamics of colliding liquid droplets by combining optical trapping, spectroscopy and high-speed color imaging. Two droplets with diameters between 5 and 50 microns are suspended in quiescent air by optical traps. The traps allows us to control the initial positions, and hence the impact parameter and the relative velocity of the colliding droplets. Movies of the droplet dynamics are recorded using high-speed digital movie cameras at a frame rate of up to 63000 frames per second. A fluorescent dye is added to one of the colliding droplets. We investigate the temporal evolution of the scattered and fluorescence light from the colliding droplets with concurrent spectroscopy and color imaging. This technique can be used to detect the exchange of molecules between a pair of neutral or charged droplets.
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| 5. |
- Johansson, Christoffer, et al.
(författare)
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The Behavior of Badminton Shuttlecocks from an Engineering Point of View
- 2018
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Ingår i: Proceedings (MDPI). - Basel Switzerland : MDPI. - 2504-3900. ; 2:6
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Konferensbidrag (refereegranskat)abstract
- This was a study of the properties of a badminton shuttle. The analysed feather was made of the brand Yonex. The properties related to the trajectory were analysed by two experiments. The first experiment provided data for the trajectory by using a camera system to capture the properties of the trajectory. Position and velocity were used to draw conclusions about the deviation to the right, as seen from the hitter. The experiment generated discrete points which made it possible to plot the data, the accuracy was estimated to ±1 cm and ±0.5 m/s. The second experiment examined the rotation of the shuttle by using a high-speed camera to capture the rotation of the shuttle. By measuring the rotation at discrete distances from the hitter, the development of the rotational speed was captured, with an accuracy of ±30 rotations per minute. The experiments described and explained a connection between sideways deviation and rotation.
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| 6. |
- Niedermeier, D., et al.
(författare)
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Observation of a link between energy dissipation rate and oscillation frequency of the large-scale circulation in dry and moist Rayleigh-Benard turbulence
- 2018
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Ingår i: Physical Review Fluids. - 2469-990X. ; 3:8
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Tidskriftsartikel (refereegranskat)abstract
- In this study both the small- and large-scale flow properties of turbulent Rayleigh-Benard convection are investigated. Experiments are carried out using the Pi chamber (aspect ratio Gamma = 2) for Rayleigh number range Ra similar to 10(8)-10(9) and Prandtl number Pr approximate to 0.7. Furthermore, experiments are run for dry and wet conditions, i.e., top and bottom surfaces of the chamber are dry and wet, respectively. For wet conditions we further distinguish between conditions with and without the presence of sodium chloride aerosol particles which, if supersaturated conditions are achieved, lead to cloud droplet formation. We therefore refer to these conditions as moist and cloudy, respectively. We see that the addition of water vapor influences the turbulent flow. In all cases, the turbulent kinetic energy dissipation rates increase with increasing temperature difference, but the slopes are different for wet and dry convection. We do not observe a clear difference between moist and cloudy convection due to low liquid water content. A similar lack of collapse with Ra is observed for the characteristic oscillations of the large-scale circulation. We observe that the first normalized characteristic oscillation frequency increased with increasing temperature difference, i.e., increasing Ra, for all conditions considered, but the slopes are different for wet and dry convection with again no clear difference between moist and cloudy convection. It turns out that the sloshing or torsional mode of the large-scale circulation and the turbulent flow or energy dissipation rate seem to be influenced by the same mechanism additional to the effect of buoyancy alone. These observational results provide supporting evidence that the large-scale circulation is insensitive to phase composition or interfacial physics and rather depends only on the strength of the turbulence.
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