共查询到20条相似文献,搜索用时 31 毫秒
1.
C. Z. ?il H. T. Eyyubo?lu Y. Baykal Y. Cai 《Applied physics. B, Lasers and optics》2009,95(4):763-771
Within the context of a general beam formulation, beam wander characteristics of cos and cosh-Gaussian beams are derived and
numerically evaluated. In our graphs, the fundamental Gaussian beam is used as a benchmark for comparisons. The associated
plots reveal that at small source sizes, a cos-Gaussian beam has the lowest beam wander, while this property is enhanced with
increasing values of the displacement parameter. At large source sizes however, this advantage is taken over by cosh-Gaussian
beam. Joint examination against the changing source sizes and propagation lengths shows that the range of source sizes, where
the beam wander of cos-Gaussian beam remains lower, is enlarged as we go toward higher propagation lengths. Asymmetric beams
tend to exhibit higher beam wanders both at small and large source sizes, but for the intermediate source size ranges, the
beam wanders of asymmetric beams will fall below those of the symmetric beams. Explanations concerning these behaviors are
offered. A historical account of beam wander formulation is also included. 相似文献
2.
By expanding the hard-aperture function into a finite sum of complex Gaussian functions, analytical formulae for the electric field of a general-type beam propagating through apertured aligned and misaligned ABCD optical systems are derived using the generalized Collins formulae, which provide a convenient way of studying the propagation of a variety of laser beams, such as Gaussian, cos-Gaussian, cosh-Gaussian, sine-Gaussian, sinh-Gaussian, flat-topped, Hermite-cosh-Gaussian, Hermite-sine-Gaussian, higher-order annular Gaussian, Hermite-sinh-Gaussian and Hermite-cos-Gaussian beams, through such optical systems. As numerical examples, the propagation properties of a cos-Gaussian beam through an apertured aligned or misaligned thin lens are studied. 相似文献
3.
Based on the generalized Huygens–Fresnel integral, analytical propagation formulas for a general-type beam propagating through aligned or misaligned ABCD optical systems in turbulent atmosphere are derived. The derived formulas provide a convenient way for studying the focusing properties of a variety of laser beams, such as Gaussian, cos-Gaussian, cosh-Gaussian, sine-Gaussian, sinh-Gaussian, flat-topped, Hermite-cosh-Gaussian, Hermite-sine-Gaussian, higher-order annular Gaussian, Hermite-sinh-Gaussian and Hermite-cos-Gaussian beams in turbulent atmosphere. As an application example, the focused intensities of cos-Gaussian, Hermite-sine-Gaussian and flat-topped beams in turbulent atmosphere are studied numerically. Focal shift of a flat-topped beam in turbulent atmosphere is investigated. Effect of the misalignment of the thin lens on the focusing properties of a cos-Gaussian beam is also explored. Our results will be useful for the applications of the general-type beam in LIDAR systems and remote sensing operating in turbulent atmosphere, where optical elements such as aligned or misaligned thin lens are commonly encountered. 相似文献
4.
The degree of polarization is found for optical excitations of cosh-Gaussian, cos-Gaussian and annular-Gaussian beams in a
turbulent atmosphere. The related formulation is based on the beam coherence polarization matrix. The self and mutual coherence
functions appearing in the beam coherence polarization matrix are evaluated, when the above mentioned excitations exhibit
partial source coherence for self and cross fields. Plots showing the variation of the degree of polarization are provided
versus the propagation length when the source size, displacement parameter, structure constant and the degree of source coherence
for self and cross fields change.
PACS 42.25.Dd; 42.25.Ja; 42.25.Kb 相似文献
5.
Partially Coherent cosh-Gaussian Beams in Atmospheric Turbulence with the Same Directionality as a Laser
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Directionality of a class of partially coherent cosh-Gaussian beams propagating in atmospheric turbulence is studied. It is shown that two partially coherent cosh-Gaussian beams may generate the same angular spread, and there exist equivalent partially coherent cosh-Gaussian beams which may have the same directionality as a fully coherent Gaussian laser beam in free space and also in atmospheric turbulence. The theoretical results are interpreted physically and illustrated numerically. 相似文献
6.
For sinusoidal beams, minimization of scintillation index is carried out against the displacements parameters. It is found that x-y asymmetric cosh-Gaussian beam fulfills the requirements of such optimum beam. Our minimization procedure reveals that the optimum beam is achieved by continually focusing it at the chosen propagation length and by further adjusting displacements parameters to be propagation distance dependent. Scintillation index of thus constructed optimum beam is formulated and numerically evaluated. Our graphical comparisons entailing collimated and focused versions of cos-, cosh-Gaussian, annular-Gaussian and Gaussian beams show that the optimum beam yields the lowest scintillations provided that propagation range is less than or equal to the focusing distance. 相似文献
7.
Guoquan Zhou 《Optics & Laser Technology》2010,42(3):489-1064
Based on the method of truncated second-order moments, the analytical expressions of the generalized beam propagation factor for truncated partially coherent cosine-Gaussian and cosh-Gaussian beams are derived. The beam propagation factors of the truncated partially coherent cosine-Gaussian and cosh-Gaussian beams depend on the acentric parameter, the truncation parameter, and the coherent parameter. According to the derived expressions, the beam propagation factors are illustrated and analyzed with numerical examples, and the influences of the different parameters on the beam propagation factors are also discussed in detail. 相似文献
8.
部分相干双曲余弦-高斯光束的传输特性和空间整形 总被引:1,自引:0,他引:1
通过加入高斯项的空间相干度,引入部分相干双曲余弦-高斯(ChG)光束,推导出部分相干ChG光束通过近轴ABCD光学系统传输的解析表达式,并用以研究其传输特性和空间整形。结果表明,部分相干ChG光束的光强分布不能保持传输不变性,其光强分布不仅与传输距离和离心参数有关,而且还与空间相干参数有关。在传输距离固定时,适当改变部分相干ChG 光束的离心参数和空间相干参数,可实现光束的空间整形。光束质量因子随空间相干性的增大和离心参数的减小而减小。高斯-谢尔模型光束和完全相干ChG光束可作为部分相干ChG光束的特例处理。 相似文献
9.
Changwei Li 《Optik》2009,120(8):374-378
Based on the propagation law of partially coherent beams, the closed-form propagation expression for partially coherent cosh-Gaussian (ChG) beams through an astigmatic lens is derived. The transformation and spatial shaping of partially coherent ChG beams through the astigmatic lens are studied and illustrated by numerical examples. It is shown that a suitable choice of the spatial coherence parameter and/or astigmatic coefficient, different beam profiles, such as Gaussian-like, flat-topped and bottle beam profiles, and beam profile with a central dip, at the geometric focal plane and at a certain plane are realizable. 相似文献
10.
The dynamic properties of cos-Gaussian beams in the presence of Kerr nonlinearity are investigated analytically and numerically using the nonlinear Schrödinger equation (NLS). Based on the moments method, evolution of a cos-Gaussian beam width in the root-mean-square (RMS) sense is obtained analytically. The beam propagation factors and the critical powers of the cos-Gaussian beams with a uniform wavefront are calculated. Using numerical simulation, it is found that although the RMS beam width broadens, the central parts of the beam give rise to an initial radial compression and a significant redistribution during propagation. The partial collapse of central parts of the beam is observed below the threshold for a global collapse. The cos-Gaussian beams eventually convert into cosh-Gaussian type beams in Kerr media with low initial power. 相似文献
11.
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
12.
For propagation in turbulent atmosphere, the radius of curvature variations for annular, dark hollow and flat topped beams
are examined under a single formulation. Our results show that for collimated beams, when examined against propagation length,
the dark hollow, flat topped and annular Gaussian beams behave nearly the same as the Gaussian beam, but have larger radius
of curvature values. Increased partial coherence and turbulence levels tend to lower the radius of curvature. Bigger source
sizes on the other hand give rise to larger radius of curvature. Dark hollow and flat topped beams have reduced radius of
curvature at longer wavelengths, whereas the annular Gaussian beam seems to be unaffected by wavelength changes; the radius
of curvature of the Gaussian beam meanwhile rises with increasing wavelength. 相似文献
13.
14.
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
15.
采用部分相干光交叉谱密度理论,给出了适用于任意大气湍流条件的斜程湍流大气传输J0相关部分相干光束在接收面内的长期平均光强分布、光束长期扩展和质量因子的解析表达式,分析了天顶角、传输距离、光源相干性以及湍流外尺度对接收面光强分布特性和光束扩展的影响.研究结果表明:在天顶角和传输距离一定的条件下,通过选择合适的光源相干性可控制焦面光强为平顶分布或中心光强为最大;在传输距离给定的条件下,随着天顶角或大气湍流外尺度的增加,焦斑光强分布均由中央凹陷分布逐渐变为高斯分布.焦面附近光强的中央凹陷比焦面的中央凹陷浅.J0相关部分相干光束实际焦斑位置随天顶角、湍流外尺度的增加以及相干性减弱而移向发射端.
关键词:
部分相干束
大气湍流
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斜程传输 相似文献
16.
Propagation and coherence properties of higher order partially coherent dark hollow beams in turbulence 总被引:3,自引:1,他引:2
Halil Tanyer Eyyubolu 《Optics & Laser Technology》2008,40(1):156-166
We formulate and evaluate in terms of graphical outputs, source and receiver plane expressions, the complex degree of coherence, beam size variation and power in bucket performance for higher order partially coherent dark hollow beams propagating in turbulent atmosphere. Our formulation is able to cover square, rectangular, circular, elliptical geometries for dark hollow and flat-topped beams in one single expression. From the graphical outputs of the receiver plane, it is observed that higher order partially coherent dark hollow beams will initially develop an outer ring around a central lobe, but will eventually evolve towards a Gaussian shape as the propagation distance is extended. It is further observed that stronger turbulence levels and greater partial coherence have similar effects on beam profile. During propagation, modulus of complex degree of coherence of partially coherent dark hollow beams appears to rise above that of the source plane values, reaching as high as near unity. Beam size analysis shows that, among the types examined, (nearly) flat-topped beam experiences the least beam expansion. Power in bucket analysis indicates that lowest order square fully coherent dark beam offers the best power capturing. 相似文献
17.
X. Chu 《Applied physics. B, Lasers and optics》2011,103(4):1013-1019
An analytical expression for arbitrary moments of the cosh-Gaussian–Shell beam in turbulent atmosphere is derived. As a special
case, kurtosis parameters of collimated and focused cosh-Gaussian beam with and without turbulent atmosphere are studied in
detail. It can be seen from the study that the kurtosis parameters of Gaussian beam do not remain constant in turbulent atmosphere.
Similar to the kurtosis parameters of a cosh-Gaussian beam at source plane, the kurtosis parameters at focal plane without
turbulent atmosphere are independent of the propagation distance and vary with the parameters of the beam. But the variation
of the kurtosis parameters at focal plane is different from that at source plane. However, the kurtosis parameters of collimated
and focused cosh-Gaussian beam both vary with the propagation distance and gradually converge to 3 along the z-axis in turbulent atmosphere. Compared with a collimated beam, the kurtosis parameters of a focused beam converge more quickly. 相似文献
18.
Suye Lü 《Optics Communications》2007,279(1):150-158
Based on the theory of optical coherence, the spatial coherence properties and directionality of partially coherent cosh-Gaussian (ChG) beams are studied. It is shown that unlike Gaussian Schell-model (GSM) beams, in the strict sense there do not exist partially coherent ChG beams which may produce the same far-field radiant intensity distribution as a fully coherent laser beam. However, under certain conditions it is possible to find partially coherent ChG beams with the same far-field radiant intensity distribution as a fully coherent laser beam. 相似文献
19.
The analytical expression of partially coherent Hermite–cosh-Gaussian (HChG) beams propagating through atmospheric turbulence is derived and used to study their propagation properties through atmospheric turbulence. It is shown that partially coherent HChG beams propagating through atmospheric turbulence undergo several stages of evolution and a decrease of the spatial correlation length speeds up the evolution process. The smaller the spatial correlation length and the larger the beam orders are, the less the beam-width spreading of partially coherent HChG beams is affected by turbulence. At a sufficiently long propagation distance the beam-width spreading of partially coherent HChG beams with smaller Ch-part parameter and smaller waist width is less affected by turbulence. The results are illustrated by numerical examples, and the validity of the results is interpreted physically. 相似文献
20.
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