Electromagnetic beam propagation in turbulent media

Fante, Ronald L.

doi:10.1109/proc.1975.10035

Cited by 483 publications

(265 citation statements)

References 171 publications

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“…So, the universal behavior of the wandering effect corresponds to the general concept that the atmosphere controls beam parameters for long-distance propagation or for the strong turbulence regime. At the same time, we see here the general tendency of the wander to decay with the increasing turbulence strength supports the reasonings of Fante [10]. He considered that when the turbulence is strong, the beam no longer wanders significantly, but rather breaks up into multiple beams.…”

Section: Theoretical Description and Calculations Of The Wander Effectsupporting

confidence: 88%

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Beam wandering in the atmosphere: The effect of partial coherence

2007

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The effect of a random phase screen on laser beam wander in a turbulent atmosphere is studied theoretically. The method of photon distribution function is used to describe the photon kinetics of both weak and strong turbulence. By bringing together analytical and numerical calculations, we have obtained the variance of beam centroid deflections caused by scattering on turbulent eddies. It is shown that an artificial distortion of the initial coherence of the radiation can be used to decrease the wandering effect. The physical mechanism responsible for this reduction and applicability of our approach are discussed.

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Section: Theoretical Description and Calculations Of The Wander Effectsupporting

confidence: 88%

“…These are averaging over the turbulence configurations, nn , and averaging over the fluctuations of the source, including fluctuations introduced by the random phase screen, f f . The first of these is determined by the known [10] expression…”

Section: Theoretical Description and Calculations Of The Wander Effectmentioning

confidence: 99%

Beam wandering in the atmosphere: The effect of partial coherence

2007

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“…The variance of the angle of arrival α on each telescope σ 2 α is directly linked to r 0 and L 0 (Fante 1975;Ziad 1993): As shown in Fig. C.1, the theoretical temporal power spectrum of the angle of arrival tends also to a f −2/3 law at low frequency while the high frequency component is characterized by a f −11/3 power law.…”

Section: Appendix B: Others Factors Reducing the Fringe Visibilitymentioning

confidence: 95%

“…Scintillation also contributes to the noise because such intensity fluctuations cannot be distinguished from the signal resulting from the fringe temporal modulation. The correlation length of the intensity fluctuations √ λh is of the order of 10 cm for a turbulence altitude h 10 km (Fante 1975). The aperture averaging effect is therefore much lower for the I2T than for large telescopes (Roddier 1981).…”

Section: Noise Propagation For Demodulation Algorithmsmentioning

confidence: 98%

Real-time optical path difference compensation at the Plateau de Calern I2T interferometer

Sorrente

Cassaing

Rousset

et al. 2001

A&A

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Abstract. The fringe tracker system of the ASSI (Active Stabilization in Stellar Interferometry) beam combining table at the I2T interferometer is described and its performance evaluated. A new real-time algorithm for the optical path difference (OPD) measurement is derived and validated. It is based on a sinusoidal phase modulation whose amplitude is optimized. It also allows automatic fringe detection at the beginning of an observation when scanning the OPD. The fringe tracker servo-loop bandwidth is adjusted by a numerical gain and ranges between 20 and 50 Hz in the reported experiments. On stars, fringe-locked sequences are limited to 20 s due to fringe jumps. However, the fringe tracker is able to recover the coherence area after a few seconds. Such a fringe tracker operation can last more than one hour. A fringe tracking accuracy of 85 nm is achieved for visibility ranging between 7 and 24%, a turbulence coherence time of approximately 9 ms at 0.85 µm, a Fried parameter of around 14 cm at 0.5 µm and an average light level of 100 000 photoevents/s, (typically visual magnitude 2 in the conditions of the experiment). Visibility losses are evaluated and are found to be mainly due to turbulent wavefront fluctuations on the two telescopes and to the static aberrations of the optical train. The measurements of OPD and angle of arrival are reduced to derive turbulence parameters: the coherence time, the average wind speed, the Fried parameter and the outer scale. Our estimations for the outer scale range between 20 and 120 m, with an average value of the order of 40 m. Both OPD and angle of arrival data, obtained on 15 m baseline and a 26 cm telescope diameter respectively, are fully compatible with the same modified Kolmogorov spectrum of the turbulence, taking into account a finite outer scale.

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“…This has been done by Fante (1975) and, subsequently, by Dios et al (2004), where they calculate the long-term (LT) beam radius as a sum of two factors, the normal diffraction one (short term; ST) and the one given by the turbulence-induced spreading of the beam:…”

Section: Fante and Yura Modelmentioning

confidence: 99%

Ground Layer Laser Seeing Meter

Cavazzani¹,

Rodeghiero²,

Capraro³

et al. 2014

Publications of the Astronomical Society of the Pacific

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ABSTRACT. The seeing calculation and its evolution during the night is a key point for the operation of telescopes and adaptive optics systems. Currently, there are various instruments able to measure the seeing, for example, the DIMM (differential image motion monitor) and the MASS (multi aperture scintillation sensor). This paper describes a new tool for the local ground layer seeing measurement. In particular, we want to derive the Fried parameter r 0 through a laser beam horizontal propagation. This is a new method for the experimental study of low-altitude atmospheric turbulence. Finally, we sketch an experimental setup for the Asiago Ekar Observatory and its possible applications.

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Electromagnetic beam propagation in turbulent media

Cited by 483 publications

References 171 publications

Beam wandering in the atmosphere: The effect of partial coherence

Beam wandering in the atmosphere: The effect of partial coherence

Real-time optical path difference compensation at the Plateau de Calern I2T interferometer

Ground Layer Laser Seeing Meter

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