Atmospheric Turbulence Characterization and Wavefront Sensing by Means of the Moiré Deflectometry

Rasouli, Saifollah

doi:10.5772/31129

Cited by 5 publications

(5 citation statements)

References 31 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Also, because of the large area of the telescope's aperture, this instrument is more suitable for studying the spatial and temporal properties of wavefronts. A potential application of the instrument in this regard is measuring anisotropy in atmospheric turbulence, which was done recently by the use of one-channel moiré deflectometry on a telescope [31]. The technique is very flexible and can be applied in a wide range of turbulence strengths by choosing gratings of adequate pitch, size, and separation.…”

Section: Discussionmentioning

confidence: 99%

“…A moiré pattern appears when two similar gratings are superimposed at a small angle or when they have slightly different periods. In many applications of the moiré pattern, one of the superimposed gratings is the image of a physical grating or is one of the self-images of the first grating [20]. By illuminating a grating with a spatially coherent light beam, exact images and many other images of the grating can be created at finite distances from the grating.…”

Section: Moiré Deflectometrymentioning

confidence: 99%

See 1 more Smart Citation

Measurement and statistical analysis of the wavefront distortions induced by atmospheric turbulence using two-channel moiré deflectometry

Dashti

Rasouli

2012

J. Opt.

Self Cite

View full text Add to dashboard Cite

Recently, an adjustable, high-sensitivity, wide dynamic range, two-channel wavefront sensor based on moiré deflectometry was proposed by Rasouli et al (2010 Opt. Express 18 23906). In this work we have used this sensor on a telescope for measuring turbulence-induced wavefront distortions. A slightly divergent laser beam passes through turbulent ground level atmosphere and enters the telescope's aperture. The laser beam is collimated behind the telescope's focal point by means of a collimator and the beam enters the wavefront sensor. First, from deviations in the moiré fringes we calculate the two orthogonal components of the angle of arrival at each location across the wavefront. The deviations have been deduced in successive frames which allows evolution of the wavefront shape and Fried's seeing parameter r 0 to be determined. Mainly, statistical analysis of the reconstructed wavefront distortions are presented. The achieved accuracy in the measurements and comparison between the measurements and the theoretical models are presented. Owing to the use of the sensor on a telescope, and using sub-pixel accuracy for the measurement of the moiré fringe displacements, the sensitivity of the measurements is improved by more than one order of magnitude. In this work we have achieved a minimum measurable angle of arrival fluctuations equal to 3.7 × 10 −7 rad or 0.07 arc s. Besides, because of the large area of the telescope's aperture, a high spatial resolution is achieved in detecting the spatial perturbations of the atmospheric turbulence.

show abstract

Section: Discussionmentioning

confidence: 99%

Section: Moiré Deflectometrymentioning

confidence: 99%

Measurement and statistical analysis of the wavefront distortions induced by atmospheric turbulence using two-channel moiré deflectometry

Dashti

Rasouli

2012

J. Opt.

Self Cite

View full text Add to dashboard Cite

show abstract

“…In many applications of the moiré pattern, one of the superimposed gratings is the image of a physical grating or is one of the self-images of the first grating (Rasouli 2012). To see animation, click on panel (Movie).…”

Section: Moiré Techniquementioning

confidence: 99%

Applications of 2-D Moiré Deflectometry to Atmospheric Turbulence

2014

JAFM

View full text Add to dashboard Cite

We report on applications of a moiré deflectometry to observations of anisotropy in the statistical properties of atmospheric turbulence. Specifically, combining the use of a telescope with moiré deflectometry allows enhanced sensitivity to fluctuations in the wave-front phase, which reflect fluctuations in the fluid density. Such phase fluctuations in the aperture of the telescope are imaged on the first grating of the moiré deflectometer, giving high spatial resolution. In particular, we have measured the covariance of the angle of arrival (AA) between pairs of points displaced spatially on the telescope aperture which allows a quantitative measure of anisotropy in the atmospheric surface layer. Importantly, the telescope-based moiré deflectometry measures directly in the spatial domain and, besides being a non-intrusive method for studying turbulent flows, has the advantage of being relatively simple and inexpensive.

show abstract

“…Moreover, contactless optical methods do not disturb the flow field. Due to the presence of density gradients, compressible fluid flow is very suitable for an investigation using optical methods that are sensitive either to the refractive index of the medium through which the light wave propagates (interferometry), or to a refractive index gradient in the medium (schlieren [7][8][9][10][11], shadowgraph [12][13][14][15][16], Moiré deflectometry [17][18][19][20][21]). Interferometric methods such as classical interferometry [22,23], holographic interferometry [24] and digital holographic interferometry [25][26][27][28][29] stand as the most accurate optical techniques [26,30,31] that are applied in many sectors of industry and scientific research, notably in the study of liquid cooling [32], diffusion [33], convection [34,35], temperature measurements and visualization [1,25,36], temperature fields measurement in pulsatile jets [25], studies of living cell imaging [37,38], precision measurement [15,39,40], vibrometry [41,42] etc.…”

Section: Introductionmentioning

confidence: 99%

Characterization of Supersonic Compressible Fluid Flow Using High-Speed Interferometry

Psota

Çubreli

Hála

et al. 2021

Sensors

View full text Add to dashboard Cite

This paper presents a very effective interference technique for the sensing and researching of compressible fluid flow in a wind tunnel facility. The developed technique is very sensitive and accurate, yet easy to use under conditions typical for aerodynamic labs, and will be used for the nonintrusive investigation of flutter in blade cascades. The interferometer employs a high-speed camera, fiber optics, and available “of-the-shelf” optics and optomechanics. The construction of the interferometer together with the fiber optics ensures the high compactness and portability of the system. Moreover, single-shot quantitative data processing based on introducing a spatial carrier frequency and Fourier analysis allows for almost real-time quantitative processing. As a validation case, the interferometric system was successfully applied in the research of supersonic compressible fluid discharge from a narrow channel in a wind tunnel. Density distributions were quantitatively analyzed with the spatial resolution of about 50 μm. The results of the measurement revealed important features of the flow pattern. Moreover, the measurement results were compared with Computational Fluid Dynamics (CFD) simulations with a good agreement.

show abstract

Atmospheric Turbulence Characterization and Wavefront Sensing by Means of the Moiré Deflectometry

Cited by 5 publications

References 31 publications

Measurement and statistical analysis of the wavefront distortions induced by atmospheric turbulence using two-channel moiré deflectometry

Measurement and statistical analysis of the wavefront distortions induced by atmospheric turbulence using two-channel moiré deflectometry

Applications of 2-D Moiré Deflectometry to Atmospheric Turbulence

Characterization of Supersonic Compressible Fluid Flow Using High-Speed Interferometry

Contact Info

Product

Resources

About