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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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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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Evaluation of lenght of the Fabry-Perot cavity with ultra-low expansion spacer with optical frequency comb
Šmíd, Radek ; Čížek, Martin ; Číp, Ondřej
The ultra-low expansion materials play a crucial role in laser stabilization and they are essential for laser stalibization. Blocks made from ultra-low expansion material are used as a base for precise interferometric measurements and in AFM microscopes. In our experiment we have monitored the free spectral range (FSR) changes and absolute length of a Fabry-Perot cavity (FPC) with a spacer made from an ultra-low expansion ceramics (Zerodur) with the expansion coefficient (CTE) of 2.8 • 10-8K-1. Experiment was carried out in the vacuum chamber at the pressure as low as 1 O'5 Pa. A fiber based femtosecond mode-locked laser with 100 MHz repetition frequency and central wavelength of 1550 nm was locked to a GPS disciplined crystal oscillator with a short term stability better than 10"12 and long term stability controlled by GPS clocks. An auxiliary tunable DFB laser diode was locked to a certain optical mode of the FPC. A beat-note signal from optical mixing between the laser and a stabilized femtosecond frequency comb is detected and processed. The absolute optical frequency of this mode is defined by saturation to acetylene cell. The FPC spacer of Zerodur material of 175 mm length was analyzed during the temperature cycling process from 22 - 35°C. Measured CTE of the spacer material was (0.069 ± 0.005) • 10-6K-1. Material exhibited hysteresis in the spacer length up to 8 nm during cycling process.
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