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Ultra-Narrow Laser for Optical Frequency Reference

100%
Lisak D., Cygan A., Bielska K., Piwiński M., Ozimek F., Ido T., Trawiński R., Ciuryło R.
Acta Physica Polonica A
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2012
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vol. 121
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issue 3
614-621
EN
We present ultra-narrow line width, tunable diode laser system which will be used as a local oscillator in an optical atomic clock and for precision spectroscopy of Sr near 689 nm. Design of the high finesse optical cavity used as short-term frequency reference is optimized with respect to insensitivity to vibrations. We achieved laser line width of about 8 Hz, measured by comparison of two identical systems. The relative phase lock of two lasers is better than 150 mHz. Laser tunability and usefulness for precison spectroscopy were demonstrated through line shape measurement of a 20 kHz wide resonance of the optical cavity.
2
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Sensing Sound Pressure in an Anechoic Chamber Using Backscattered Laser Light

80%
Piper B., Koukoulas T.
Acta Physica Polonica A
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2015
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vol. 127
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issue 1
128-131
EN
Current standards for the measurement of the SI derived unit of sound-in-air pressure, the pascal, are based upon microphone reciprocity calibration and are achieved indirectly through microphone sensitivity. These methods require microphones of specific geometry and performance characteristics, effectively artefacts, and are traceable through standards for electrical and dimensional units. Measurement of acousto-optic interactions can provide a direct approach to measuring sound pressure. One acousto-optic interaction is the periodic scattering of photons caused by particles moving in a sinusoidal manner due to propagating sound across interference fringes formed at the intersection of two coherent laser beams. The sequence of these scattered photons, which is collected using telescopic optics and generated by a single photon counting device, can be autocorrelated to yield the periodicity of the photon events. Through mathematical analysis of the autocorrelation function it has been shown that acoustic particle velocity is inversely proportional to the time of the first minimum. This has effectively been shown for measurements in acoustic standing wave tubes and has been developed into a method which can be applied in an anechoic chamber. This paper describes the design and implementation of such a system which allows for a comparison of sound pressure measurements using optical and microphone based techniques.
3
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Phototermal Spectra of Inhomogeneous Coatings

80%
Popovic M., Galovic S., Stojanovic Z.
Acta Physica Polonica A
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2009
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vol. 116
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issue 4
535-537
EN
In this paper we demonstrate a theoretical study for photothermal measurements on inhomogeneous coatings. First, a general photothermal mathematical model for thermal gradient materials is presented. Then, we discuss the effects of inhomogeneous thermal properties in photothermal amplitude and phase spectra of coatings. Finally, a method for quantitative depth profiling that makes use of prior knowledge about the type of profile existing in a sample to reduce the instabilities associated with the mathematically ill conditioned task is demonstrated.
4
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Planar Optical Waveguide Sensor Structures with Grating Couplers

80%
Karasiński P.
Acta Physica Polonica A
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2009
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vol. 116
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issue S
S-30-S-32
EN
The paper presents optical planar waveguide sensor structures with grating couplers of groove density χ = 2400 g/mm. The waveguide films were obtained using sol-gel method, in which the grating couplers were fabricated by the embossing method. The results of theoretical analysis as well as the results of experimental research have been presented.
5
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Laser Sheet Scattering and the Cameras' Positions in Particle Image Velocimetry

80%
Ilić J., Čantrak D., Srećković M.
Acta Physica Polonica A
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2007
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vol. 112
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issue 5
1113-1118
EN
Simulations of laser sheet scattering by microparticles, based on the generalized Lorenz-Mie theory for the case of numerous random spatial distributions of scattering particles, were done, using the novel computational time saving strategy. This type of scattering by particles immersed in a fluid flow and its recording on cameras, presents the essence of particle image velocimetry systems. The continuous and large change of the intensity of a scattered light falling on the camera causes the sequences of images of varying quality, which makes many of them useless. This paper shows how the problem could be alleviated by determining the angles of low relative standard deviation of scattered light intensity and using them for recording, as well as by avoiding the angles of high relative standard deviation of scattered light intensity.
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