Application of speckling for measuring the deflection of laser light by phase objects

Kopf, U.

doi:10.1016/0030-4018(72)90030-2

Cited by 72 publications

(19 citation statements)

References 4 publications

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“…18,19 A special case is the estimation of a plasma density profile for fusion plasma devices and measuring the laser deflection by phase objects. 20,21 Previously mentioned methods treat light refraction effects and schlieren measurements mostly qualitatively, although they do report about using Abel's transformation for the diagnostics. However, in these cases, the problem to separate the effects of gas temperature and density of charge particles in the plasma remains unsolved.…”

Section: Introductionmentioning

confidence: 99%

Laser schlieren deflectometry for temperature analysis of filamentary non-thermal atmospheric pressure plasma

Schäfer

Foest

Reuter

et al. 2012

Review of Scientific Instruments

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The heat convection generated by micro filaments of a self-organized non-thermal atmospheric pressure plasma jet in Ar is characterized by employing laser schlieren deflectometry (LSD). It is demonstrated as a proof of principle, that the spatial and temporal changes of the refractive index n in the optical beam path related to the neutral gas temperature of the plasma jet can be monitored and evaluated simultaneously. The refraction of a laser beam in a high gradient field of n(r) with cylindrical symmetry is given for a general real refraction index profile. However, the usually applied Abel approach represents an ill-posed problem and in particular for this plasma configuration. A simple analytical model is proposed in order to minimize the statistical error. Based on that, the temperature profile, specifically the absolute temperature in the filament core, the FWHM, and the frequencies of the collective filament dynamics are obtained for non-stationary conditions. For a gas temperature of 700 K inside the filament, the presented model predicts maximum deflection angles of the laser beam of 0.3 mrad which is in accordance to the experimental results obtained with LSD. Furthermore, the experimentally obtained FWHM of the temperature profile produced by the filament at the end of capillary is (1.5 ± 0.2) mm, which is about 10 times wider than the visual radius of the filament. The obtained maximum temperature in the effluent is (450 ± 30) K and is in consistence with results of other techniques. The study demonstrates that LSD represents a useful low-cost method for monitoring the spatiotemporal behaviour of microdischarges and allows to uncover their dynamic characteristics, e.g., the temperature profile even for challenging diagnostic conditions such as moving thin discharge filaments. The method is not restricted to the miniaturized and self-organized plasma studied here. Instead, it can be readily applied to other configurations that produce measurable gradients of refractive index by local gas heating and opens new diagnostics prospects particularly for microplasmas.

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Section: Introductionmentioning

confidence: 99%

Laser schlieren deflectometry for temperature analysis of filamentary non-thermal atmospheric pressure plasma

Schäfer

Foest

Reuter

et al. 2012

Review of Scientific Instruments

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“…The BOS technique can best be compared with laser speckle density photography as described by Debrus et al (1972) and Köpf (1972) and the improved versions by Wernekinck and Merzkirch (1987) and Viktin and Merzkirch (1998). Like most interferometric techniques, laser speckle density photography preferably utilizes an expanded parallel laser beam, which traverses a compressible flow field or (in more general terms) passes through an object of varying refractive index (i.e., a phase object).…”

Section: Bos Theorymentioning

confidence: 99%

Background-oriented schlieren (BOS) techniques

2015

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“…The technique is based on the distortion of one image, due to density changes, compared to an undistorted reference image. This approach can best be compared with laser speckle density photography, as described by Køpf (1972) and Wernekink and Merzkirch (1987). The processing of the images is shown in Fig.…”

Section: Background-oriented Schlieren Measurementsmentioning

confidence: 99%

Optical density and velocity measurements in cryogenic gas flows

2005

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This paper presents the application of optical measurement techniques in dense-gas flows in a heavygas channel to determine planar two-component (2C) velocity profiles and two-dimensional (2D) temperature profiles. The experimental approach is rather new in this area, and represents progress compared with the traditional techniques based on thermocouple measurements. The dense-gas flows are generated by the evaporation of liquid nitrogen. The optical measurement of both the velocity and density profiles is accomplished by the implementation of particle image velocimetry (PIV) and background-oriented schlieren (BOS) systems. Supplemental thermocouple measurements are used as independent calibrations to derive temperatures from the density data measured with the BOS system. The results obtained with both systems are used to quantify the dilution behavior of the propagating cloud through a global entrainment parameter b. Its value agrees well with the results obtained by earlier studies.

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Application of speckling for measuring the deflection of laser light by phase objects

Cited by 72 publications

References 4 publications

Laser schlieren deflectometry for temperature analysis of filamentary non-thermal atmospheric pressure plasma

Laser schlieren deflectometry for temperature analysis of filamentary non-thermal atmospheric pressure plasma

Background-oriented schlieren (BOS) techniques

Optical density and velocity measurements in cryogenic gas flows

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