共查询到20条相似文献,搜索用时 54 毫秒
1.
Scintillation evaluations for Laguerre-Gaussian (LG) beams for slant paths are made using Rytov approximation. On- and off-axis scintillation is formulated and calculated up to several tens of kilometers of slant distances for different zenith angles. Scintillation index variations against radial receiver point and different source sizes are also investigated. In all cases evaluated, it is found that LG beams with higher radial mode numbers result in less scintillation than Gaussian beam. Kolmogorov spectrum function is utilized in the scintillation calculations. 相似文献
2.
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
3.
By means of numerical simulations, we analyze the scintillation characterization for multiple incoherent uplink Gaussian beams under weak fluctuations cases. Because truly independent beams are difficult to create, we present a more general but approximate model for the multiple of beams traveling through partially correlated paths. This model compares with wave-optics simulations and highlights the reduced correlation coefficient as the beam separation is increased. The scintillation index of three and six incoherent uplink Gaussian beams is also induced. The result shows that the scintillation index decreases with the increase of beams amount and beam separation. When the beams amount and strength of atmospheric turbulence are fixed, the reduction of scintillation index is affected by the ratio of beams separation and the Fried length. The corresponding physical mechanisms for the results are discussed. 相似文献
4.
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
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.
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
7.
The scintillation properties of astigmatic annular beams in a weak turbulent atmosphere are investigated. Expression for the on-axis scintillation index of an astigmatic annular beam is derived. It is found that the scintillation index of an astigmatic annular beam can be smaller than that of a Gaussian beam, an elliptical Gaussian beam and a stigmatic annular beam in a weak turbulent atmosphere under certain conditions. The scintillation properties of astigmatic annular beams are closely controlled by its beam parameters. 相似文献
8.
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
9.
10.
11.
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
12.
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
13.
We investigate the optical trapping effect of high-order Laguerre-Gaussian (LG) beams acting on a dielectric sphere in Rayleigh regime. For LG beams with the azimuthal mode index l=0, it is found that under the same input power, the transverse trapping effect can be enhanced several times with increasing the radial mode index p, compared with that of the Gaussian beam; while its axial trapping effect is exactly the same as that of Gaussian beam, although the central trapping region reduces as p increases. For LG beams with l≥1, we find that the maximal transverse gradient forces increase with the increasing of p and the axial radiation forces reduces slightly, therefore an optimal choose on p and l is necessary for obtaining an optimal optical guiding. Our result is useful for analyzing the trapping efficiency of LG beams applied in micromanipulation technologies. 相似文献
14.
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
15.
The scintillation index of vortex beam in simulated atmospheric turbulence is experimentally investigated. The fluctuation of the intensity can be effectively reduced by vortex beams. In particular, the reduction of scintillation is more pronounced for vortex beams with larger topological charge. 相似文献
16.
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
17.
Based on the relations between Laguerre–Gaussian (LG) and Hermite–Gaussian (HG) modes and by introduced the complex Gaussian
expansion method for two dimensional rectangular aperture, the approximate analytical propagation expressions of the rotational
symmetrical LG beams along with their even and odd modes through a paraxial ABCD optical system with rectangular hard-edged aperture are derived. As special cases of the results, the corresponding closed-forms
of the circular aperture diffracted LG beams and non-truncated LG beams are also given. Numerical examples are given to prove
the validity of this approximate analytical method and illustrate the propagation properties of the rectangular hard-edged
aperture diffracted LG beams. 相似文献
18.
理论研究了激光光束经过湍流大气后闪烁系数的变化规律,以ARM7的嵌入式系统构建数据采集模块,在采集激光光强因为大气湍流影响而变化的数据的基础上对存储的数据使用闪烁系数数学模型进行运算,运算结果通过网络传输,由PC端的界面显示变化曲线,从而了构造一个可以感测大气湍流的远程探测系统。用转动的相位板模拟湍流大气,利用所开发的测试系统测量激光光束通过湍流大气后的闪烁系数。实验结果显示高斯光束在湍流大气中的闪烁系数随传输距离的增加而增大,与理论模拟结果基本相符。由此可见该系统工作可靠稳定,可实时测量激光光束经过湍流大气的闪烁系数。 相似文献
19.
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
20.
本文采用分步相位屏方法来仿真椭圆涡旋光束在海洋中的实际传输情况,并对椭圆涡旋光束在海洋湍流中的传输光强和闪烁因子进行了仿真。研究发现,椭圆涡旋光束在海洋传输过程中,光斑会发生明显的旋转,同时光斑会产生暗核且暗核个数与光束的拓扑荷数相等。一个拓扑荷数为m的相位奇点会分裂成m个拓扑荷数为1的相位奇点,并且海洋湍流越强,光斑受到的干扰越严重。研究还发现,在较弱的海洋湍流中,随着传输距离的增加,椭圆涡旋光束的闪烁因子会低于高斯光束和涡旋光束的闪烁因子,而且在远距离处拓扑荷数越大闪烁因子降低越明显,同时也发现,传播一段距离后涡旋光束的闪烁因子会低于高斯光束的闪烁因子。在较强湍流中,椭圆涡旋光束的闪烁因子会交叠在一起。对于不同强度的海洋湍流,随着均方温度耗散率的增大,椭圆涡旋光束的轴上点闪烁因子也增大。在同一传输距离处,束腰宽度越小的椭圆涡旋光束闪烁因子越小。 相似文献