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Cooling of thermal motion of optically levitated nanoobjects
Zemánková, Tereza ; Flajšmanová, Jana (oponent) ; Jonáš, Alexandr (vedoucí práce)
The master's thesis deals with optical levitation of dielectric nanoparticles and cooling of their thermal motion. By focusing two counter-propagating laser beams, the particle can be stably trapped between the foci of the two beams. By subsequently applying an external electric field to the optically trapped charged particle and properly adjusting the feedback loop, it is possible to remove energy from the particle, reduce its position variance, and thus cool the particle thermal motion. The thesis is divided into three main chapters. The first discusses the theoretical introduction to optical trapping, describes the dynamics of the trapped particle, and connects it to the experimental section. A schematic of the experimental setup, preparation of particles for experiments, detection of the particle position, instructions on how to properly tune the optical setup, and calibration of the data to SI units are described. In the second part, various methods of cooling the thermal motion of an optically levitating particle are presented. Experiments performed with a single captured particle are compared with the theoretical model. In a laser beam with circular profile, the particle was cooled in one axis and the elliptical profile of the beam allowed cooling the thermal motion of the particle in two axes. In the third part, the trapping and interaction of two levitating particles, the formation of normal modes and their subsequent cooling are discussed. The experimentally obtained data are compared with theoretical models.
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Opticky zachycené laditelné kapénkové mikrolasery
Ježek, Jan ; Pilát, Zdeněk ; Brzobohatý, Oto ; Jonáš, Alexandr ; Aas, M. ; Kiraz, A. ; Zemánek, Pavel
Emulzní mikrokapénky, které se nemísí s okolní nosnou kapalinou, přestavují dokonalé kulové mikroobjekty s ideálně hladkým optickým povrchem. Lze v nich vybudit speciální mody (tzv. Whispering Gallery Modes - WGM) s extrémně vysokým činitelem jakosti a následně velmi úzkou spektrální odezvou. Jsou-li tyto kapénky vhodně fluorescenčně obarveny a opticky čerpány, jednotlivé WGM fungují jako kruhové rezonátory, ve kterých se generuje koherentní záření. Takový kapénkový mikrolaser představuje miniaturní zdroj koherentního záření, který lze bezkontaktně přemísťovat a jehož emisní spektrum je extrémně citlivé na změny velikosti, tvaru a rovněž indexu lomu v okolí povrchu kapénky.
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Study of mechanical properties and dynamics of biomembranes and single molecules with the use of laser beam - an overview
Jonáš, Alexandr ; Zemánek, Pavel
A micron-sized dielectric particle confined in a laser trap can be employed as a probe for the measurement of forces in the range from piconewtons to hundreds of piconewtons. Thus, if a biological system of interest (e.g. DNA molecule, single myosin or kinesin molecule, cell membrane) is attached to such a probe, its mechanical and dynamical properties (elasticity, viscosty, forces associated with movement) can be studied during its interaction with the environment with unprecedented resolution. This article introduces the basic principles of the laser trapping and force measurement and illustrates on several examples the great potential of the light-based force transducer for exploiting non-invasively the dynamics of basic biological systems.
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Study of the Behaviour of Microparticle in the Standing Wave Trap
Ježek, Jan ; Jonáš, Alexandr ; Zemánek, Pavel ; Liška, M.
The basic behavior of microparticles placed in the Gaussian standing wave is studied theoretically and experimentally in this article. It is shown that the optical force depends periodically on the particle size and, as the consequence, the equilibrium object position is alternating between the standing wave antinodes and nodes. For certain particle sizes, the particle confinement is disabled. Experimental confirmation of the theoretical results is briefly discussed.
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Measurement of the Optical Trap Stiffness
Jákl, Petr ; Jonáš, Alexandr ; Zemánek, Pavel ; Liška, M.
An optical trap for dielectric microparticles is usually approximated by a parabolic potential well, whose profile is characterized by a single constant - trap stiffness. This stiffness can be estimated using several methods, including Fourier spectral analysis of the thermal noise of the trapped particle position, or method based on equipartition theorem. The principles of the trap calibration and experimental results are presented.
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