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Nanopositioning with detection of a standing wave
Holá, M. ; Hrabina, J. ; Číp, O. ; Fejfar, Antonín ; Stuchlík, Jiří ; Kočka, Jan ; Oulehla, J. ; Lazar, J.
A measuring technique is intended for displacement and position sensing over a limited range with detection of standing-wave pattern inside of a passive Fabry-Perot cavity. In this concept we consider locking of the laser optical frequency and the length of the Fabry-Perot cavity in resonance. Fixing the length of the cavity to e.g. a highly stable mechanical reference allows stabilizing wavelength of the laser in air and thus to eliminate especially the faster fluctuations of refractive index of air due to air flow and inhomogeneity. Detection of the interference maxima and minima within the Fabry-Perot cavity along the beam axis has been tested and proven with a low loss transparent photodetector with very low reflectivity. The transparent photodetector is based on a thin polycrystalline silicon layer. Reduction of losses was achieved thanks to a design as an optimized set of interference layers acting as an antireflection coating. The principle is demonstrated on an experimental setup.
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Detection standing wave within Fabry-Perot Cavity
Holá, Miroslava
This contribution follows up with project Interferometry with compensation of the refractive index of air. This inteferometric technique was based on differential interferometry setup for measurement in the subnanometer scale in atmospheric conditions. One of the important limiting factor in any optical measurement are fluctuations of the refractive index of air representing a source of uncertainty on the 10-6 level when evaluated indirectly from the physical parameters of the atmosphere. Our proposal is based on the concept of overdetermined interferometric setup where the reference length is derived from a mechanical frame made from a material with very low thermal coefficient on the 1*E-8 level (Zerodur - Schott). The optical setup consists of three interferometers sharing the same beam path where two measurement differentially the displacement while the third evaluates the changes in the measuring range acting as a tracking refractometer. The concept of stabilization of wavelength against the mechanical reference is realized within passive Fabry-Perot cavity. The link between the wavelength and mechanical reference here is in principle simple, the laser optical frequency has to be locked to the resonance of the passive cavity either through tracking the transmission maximum or reflection minimum. The key component for position sensing inside of a passive Fabry-Perot cavity is low-loss transparent photodetector. The transparent photodetector made in cooperation with Institute of Physics of the ASCR - Department of Thin Films and Nanostructures (work group A. Fejfar). Transparent photodetector is made of fused silica substrate, active photo resistive silicon layer with side titanium electrode and a set of antireflection coatings optimized for minimum reflectivity. Optimized AR coating for 532 nm.
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Nanopositioning with detection of a standing wave
Holá, Miroslava ; Hrabina, Jan ; Číp, Ondřej ; Fejfar, A. ; Stuchlík, J. ; Kočka, J. ; Oulehla, Jindřich ; Lazar, Josef
A measuring technique is intended for displacement and position sensing over a limited range with detection of standing-wave pattern inside of a passive Fabry-Perot cavity. In this concept we consider locking of the laser optical frequency and the length of the Fabry-Perot cavity in resonance. Fixing the length of the cavity to e.g. a highly stable mechanical reference allows stabilizing wavelength of the laser in air and thus to eliminate especially the faster fluctuations of refractive index of air due to air flow and inhomogeneity. Detection of the interference maxima and minima within the Fabry-Perot cavity along the beam axis has been tested and proven with a low loss transparent photodetector with very low reflectivity. The transparent photodetector is based on a thin polycrystalline silicon layer. Reduction of losses was achieved thanks to a design as an optimized set of interference layers acting as an antireflection coating. The principle is demonstrated on an experimental setup.
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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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