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1.
Scintillations of Laguerre–Gaussian (LG) beams for weak atmospheric turbulence conditions are derived for on-axis receiver positions by using Huygens–Fresnel (HF) method in semi-analytic fashion. Numerical evaluations indicate that at the fully coherent limit, higher values of radial mode numbers will give rise to more scintillations, at medium and low partial coherence levels, particularly at longer propagation distances, scintillations will fall against rises in radial mode numbers. At small source sizes, the scintillations of LG beams having full coherence will initially rise, reaching saturation at large source sizes. For LG beams with low partial coherence levels, a steady fall toward the larger source sizes is observed. Partially coherent beams of medium levels generally exhibit a rising trend toward the large source sizes, also changing the respective positions of the related curves. Beams of low coherence levels will be less affected by the variations in the refractive index structure constant. 相似文献
2.
In strong atmospheric turbulence, the asymptotic on-axis scintillation behaviors of Laguerre Gaussian (LG) beams are examined.
To arrive at the strong-turbulence solution, we utilize the existing filtering approach for weak-turbulence solutions and
our recently reported weak-turbulence scintillation index formula for LG beams. In the limiting case, our solution correctly
predicts the asymptotic strong-turbulence behavior of Gaussian beam wave scintillation. Investigation of the scintillations
versus the propagation distance, source size, wavelength and refractive index structure parameter lead to the conclusion that
the LG beams with higher order radial modes can provide less scintillation. The results are applicable to long-haul atmospheric
optical communication links. 相似文献
3.
Halil T. Eyyubo?lu 《Applied physics. B, Lasers and optics》2011,103(3):763-769
For the strong atmospheric turbulence regime, the asymptotic on-axis scintillation behavior of annular, cosh and cos Gaussian
beams is theoretically derived and illustrated with numerical examples. It is observed from the plots that annular Gaussian
beams exhibit more scintillations than a Gaussian beam, regardless of the amplitude coefficient and source size settings.
For small source sizes, cosh Gaussian beams seem to have an advantage over Gaussian beams in terms of reduced scintillation,
but for large source sizes a switchover occurs where cos Gaussian beams assume the advantage. Analysis of the effect of inner
scale value shows that scintillations increases for all beams as the inner scale increases. 相似文献
4.
H.T. Eyyubolu Y. Baykal E. Sermutlu Y. Cai 《Applied physics. B, Lasers and optics》2008,92(2):229-235
For a weak turbulence propagation environment, the scintillation index of the lowest order Bessel–Gaussian beams is formulated.
Its triple and single integral versions are presented. Numerical evaluations show that at large source sizes and large width
parameters, when compared at the same source size, Bessel–Gaussian beams tend to exhibit lower scintillations than the Gaussian
beam scintillations. This advantage is lost however for excessively large width parameters and beyond certain propagation
lengths. Large width parameters also cause rises and falls in the scintillation index of off-axis positions toward the edges
of the received beam. Comparisons against the fundamental Gaussian beam are made on equal source size and equal power basis.
PACS 42.25.Dd; 42.25.Bs; 42.68.Bz; 42.68.-w 相似文献
5.
We present scintillation calculations in weak atmospheric turbulence for partially coherent general beams based on the extended
Huygens–Fresnel integral and a Matlab function designed to handle expressions both of the average intensity and the average
squared intensity. This way, the integrations are performed in a semi-analytic manner by the associated Matlab function, and
this avoids lengthy, time-consuming and error prone hand derivations. The results are obtained for the partially coherent
fundamental and higher-order sinusoidal and annular Gaussian beams. By plotting the scintillation index against the propagation
distance and source size, we illustrate the on-axis scintillation behaviors of these beams. Accordingly, it is found that
within specific source and parameter ranges, partially coherent fundamental, higher-order sinusoidal and annular Gaussian
beams are capable of offering less scintillations, in comparison to the fundamental Gaussian beam. 相似文献
6.
H. T. Eyyubo?lu 《Applied physics. B, Lasers and optics》2010,98(1):203-210
As an extension of our previous study, the area scintillation aspects of Bessel Gaussian and modified Bessel Gaussian beams
of zeroth order are investigated. The analysis is carried out on the basis of equal source sizes and equal source powers.
It is found that, when compared on equal source size basis, modified Bessel Gaussian beams always have less area scintillations
than a Gaussian beam, while Bessel Gaussian beams exhibit more area scintillations. Comparison on equal source power basis,
however, removes the advantage of modified Bessel Gaussian beams, that is, their area scintillations become nearly the same
as those of the Gaussian beam. On the other hand, for the case of equal source powers, Bessel Gaussian beams with larger width
parameters continue to have higher area scintillations than the Gaussian beam. We provide graphical illustrations for profiles
of equal source size beams, equal source power beams and the curves to aid the selection of equal source power beams. 相似文献
7.
H. T. Eyyubo?lu 《Applied physics. B, Lasers and optics》2011,103(3):755-762
We study the scintillation aspects of partially coherent Lorentz Gaussian (LG) beams via numerically integrating the average
and average squared intensity expressions. Within the examined range of input and propagation medium parameters, the LG beams
are generally found to offer less and less scintillations against the pure Gaussian beam, particularly when the Lorentzian
feature of the beam is emphasized more. This lower scintillation property is exhibited for collimated coherent beams with
different Lorentz widths and at on-axis and off-axis positions of the receiver plane. When focusing is introduced, at shorter
propagation distances the ordering of the beams remains as described above, but at longer propagations distances a complete
reversing of the beam order is observed. Raising the turbulence levels by increasing the structure constant inevitably causes
rises in scintillations, while preserving the advantage of LG beams over the pure Gaussian beam. Partial coherence reduces
scintillations as expected, at the same time nearly eliminating the scintillation differences between the beam types. 相似文献
8.
The scintillation index of a laser array beam is analytically derived and numerically evaluated for weak turbulence conditions.
On-axis as well as off-axis positions of the receiver plane are considered. Our graphical illustrations prove that at longer
propagation ranges and at some midrange radial displacement parameters, laser array beams exhibit less scintillations, when
compared to a fundamental Gaussian beam. However, when compared among themselves, laser array beams tend to have reduced scintillations
with rising numbers of beamlets, longer propagation wavelengths, at midrange radial displacement parameters, at intermediate
Gaussian source sizes, at bigger inner scales and smaller outer scales of turbulence. However, in this improvement, the number
of beamlets does not seem to have a major role.
PACS 42.25.Dd; 42.25.Ja; 42.25.Kb 相似文献
9.
Halil T. Eyyubo?lu 《Applied physics. B, Lasers and optics》2012,106(1):161-169
We provide the scintillation formulation for a multiwavelength source. Within this context, the scintillation aspects of Gaussian,
cos, cosh and annular Gaussian beams are investigated. For all situations examined, it is found that for a source comprising
many wavelengths, there will be less scintillations as compared to a single wavelength source of the lowest wavelength and
but the reverse will be true if the comparison is with respect to the single wavelength source of the highest wavelength.
The same is observed at all propagation distances, source sizes, on-axis and off-axis positions considered. Additionally,
it is seen that the scintillation characteristics of multiwavelength sources will follow similar trends of single wavelength
sources. The analysis is based on the Rytov approximation, therefore our results are valid for conditions of weak atmospheric
turbulence. 相似文献
10.
?. Arpali S. A. Arpali Y. Baykal H. T. Eyyubo?lu 《Applied physics. B, Lasers and optics》2011,103(1):237-244
The intensity fluctuation of a partially coherent laser beam array is examined. For this purpose, the on-axis scintillation
index at the receiver plane is analytically formulated via the extended Huygens–Fresnel diffraction integral in conditions
of weak atmospheric turbulence. The effects of the propagation length, number of beamlets, radial distance, source size, wavelength
of operation and coherence level on the scintillation index are investigated for a horizontal propagation path. It is found
that, regardless of the number of beamlets, the scintillation index always rises with an increasing propagation length. If
laser beam arrays become less coherent, the scintillation index begins to fall with growing source sizes. Given the same level
of partial coherence, slightly less scintillations will occur when the radial distance of the beamlets from the origin is
increased. At partial coherence levels, lower scintillations are observed for larger numbers of beamlets. Both for fully and
partially coherent laser beam arrays, scintillations will drop on increasing wavelengths. 相似文献
11.
Scintillation index of partially coherent annular and partially coherent flat-topped Gaussian beams propagating in horizontal links is found at the receiver origin when these beams propagate in extremely strong atmospheric turbulence. Scintillation index of coherent versions of such beams attain unity saturation value whereas the decrease in the degree of source coherence results in the decrease of the scintillations. At a fixed degree of partial coherence, thin ring sized annular beams possess smaller scintillations than thick ones. For partially coherent flat-topped Gaussian beams, higher flatness yields smaller intensity fluctuations. In extremely strong turbulence, partially coherent annular and partially coherent flat-topped Gaussian beams have smaller scintillations when compared to partially coherent single Gaussian beam scintillations. 相似文献
12.
The effect of spherical aberration on scintillations of Gaussian beams in weak, moderate and strong turbulence is studied using numerical simulation method. It is found that the effect of the negative spherical aberration on the on-axis scintillation index is quite different from that of the positive spherical aberration. In weak turbulence, the positive spherical aberration results in a decrease of the on-axis scintillation index on propagation, but the negative spherical aberration results in an increase of the on-axis scintillation index when the propagation distance is not large. In particular, in weak turbulence the negative spherical aberration may cause peaks of the on-axis scintillation index, and the peaks disappear in moderate and strong turbulence, which is explained in physics. The strong turbulence leads to less discrepancy among scintillations of Gaussian beams with and without spherical aberration. 相似文献
13.
H. T. Eyyubo?lu 《Applied physics. B, Lasers and optics》2009,96(2-3):301-308
Stemming from the results of our earlier investigations, the concept of area scintillation is introduced, which takes into account the intensity distribution over the receiver plane. In this context, the area scintillation of fundamental Gaussian and annular beams is formulated, numerically evaluated and graphically illustrated. From the comparison, it is seen that, under the same source power conditions, annular Gaussian beams provide much less scintillations than the fundamental Gaussian beams at small source size. At large source sizes and at shorter propagation distances, annular beams are still favorable, but, as the propagation range is extended, the reverse becomes true. A review of previous findings leading up to the newly introduced concept is also presented. 相似文献
14.
Benefiting from the earlier derivations for the Gaussian beam, we formulate beam wander for dark hollow (DH) and flat-topped (FT) beams, also covering the annular Gaussian (AG) beam as a special case. Via graphical illustrations, beam wander variations of these beams are analyzed and compared among themselves and to the fundamental Gaussian beam against changes in propagation length, amplitude factor, source size, wavelength of operation, inner and outer scales of turbulence. These comparisons show that in relation to the fundamental Gaussian beam, DH and FT beams will exhibit less beam wander, particularly at small primary beam source sizes, lower amplitude factors of the secondary beam and higher beam orders. Furthermore, DH and FT beams will continue to preserve this advantageous position all throughout the considered range of wavelengths, inner and outer scales of turbulence. FT beams, in particular, are observed to have the smallest beam wander values among all, up to certain source sizes. 相似文献
15.
X.P. Zhang W. Wang Y.J. Xie P.X. Wang Q. Kong Y.K. Ho 《Optics Communications》2008,281(15-16):4103-4108
The electric field intensity distribution and the phase velocity distribution of high-order Laguerre–Gaussian (LGρ?) mode laser beams are analyzed. Using three-dimensional test particle simulation, the numerical results of electrons accelerated by LG00, LG40 and LG41 mode laser beams are presented. Compared with the LG00 mode (the fundamental mode) laser beam, low-energy injection electrons can be more favorably accelerated in a high-order LG mode laser beam. Contrary to anticipation, a high-order LG mode laser beam with intense axial electric field distribution is inferior to the LG00 mode in capture acceleration for electrons with high injection energy. 相似文献
16.
17.
Mikhail I. Charnotskii 《Waves in Random and Complex Media》1994,4(3):243-273
Asymptotic analysis of on-axis intensity fluctuation variance of a finite-sized light beam is performed starting from the functional integral representation for the field in a random medium. Collimated, diverging and converging beams with different diffraction properties are considered. A complete set of asymptotes is obtained using the main and additional coherence channels approach to the fourth moment of field analyses. We study the conditions of weak and strong fluctuation regimes for all these types of beams and obtain relatively simple formulae for on-axis intensity variance, which are valid for the case of stratified turbulence. It is shown that scintillations in the vicinity of the beam focus are governed by double-scattering processes for weak scintillations and double scattering from coherence channels for strong fluctuations. 相似文献
18.
Using laser beams with less than perfect spatial coherence is an effective way of reducing scintillations in free-space optical communication links. We report a proof-of-principle experiment that quantifies this concept for a particular type of a partially coherent beam. In our scaled model of a free-space optical communication link, the beam is composed of several partially overlapping fundamental Gaussian beams that are mutually incoherent. The turbulent atmosphere is simulated by a random phase screen imprinted with Kolmogorov turbulence. Our experiments show that for both weak-to-intermediate and strong turbulence an optimum separation between the constituent beams exists such that the scintillation index of the optical signal at the detector is minimized. At the minimum, the scintillation reduction factor compared with the case of a single Gaussian beam is substantial, and it is found to grow with the number of constituent beams. For weak-to-intermediate turbulence, our experimental results are in reasonable agreement with calculations based on the Rytov approximation. 相似文献
19.
In a weakly turbulent atmosphere governed by the non-Kolmogorov spectrum, the on-axis scintillation index is formulated and
evaluated when the incidence is an annular Gaussian type. When the power law of the non-Kolmogorov spectrum is varied, the
scintillation index first increases, and reaches a peak value, then starts to decrease, and eventually approaches zero. The
general trend is that when turbulence has a non-Kolmogorov spectrum with power law larger than the Kolmogorov power law, the
scintillation index values become smaller. For all power laws, collimated annular Gaussian beams exhibit smaller scintillations
when compared to pure Gaussian beams of the same size. Intensity fluctuations at a fixed propagation distance diminish for
the non-Kolmogorov spectrum with a very large power law, irrespective of the focal length and the thickness of optical annular
Gaussian sources. 相似文献
20.
H. T. Eyyubo?lu 《Applied physics. B, Lasers and optics》2012,108(2):335-343
For a non-Kolmogorov spectrum, scintillation aspects of cos, cosh and annular Gaussian beams are investigated. The appropriate mathematical formulation is developed, the derived scintillation index is evaluated and its variation is plotted in graphs. We find that, when the values of the power coefficient of the spectrum are just above 3, low scintillation is encountered, then as the power coefficient is increased, rises will occur with a peak being reached around 3.21. From there onwards, scintillation will drop, as the power coefficient approaches a value of 5. For extreme off-axis positions, there will be slight increases in scintillation at high power coefficient values. At points near on-axis and when the beams have small width sizes, cosh Gaussian beam having a bigger displacement parameter will offer the lowest scintillation. At large width sizes, this advantage will switch to the side of the cos Gaussian beam. In this study, the variation of scintillation with other sources and propagation parameters is examined as well. 相似文献