發(fā)布時間：2017-12-31 14:16

  本文關鍵詞：激光大氣傳輸中的相位奇點和光學渦旋及其演化特性研究　出處：《山東師范大學》2016年博士論文　論文類型：學位論文

  更多相關文章： 大氣光學 奇點光學 大氣傳輸 大氣湍流 相位奇點 光學渦旋

【摘要】：激光在湍流大氣中傳輸時,光波的振幅和相位會發(fā)生隨機起伏,導致接收平面處光場的光強起伏及相位畸變等。在強湍流效應條件下,畸變光場中會出現(xiàn)一些光強為零且相位不確定的點,這些點被稱為相位奇點。相位奇點的存在給傳統(tǒng)自適應光學系統(tǒng)的波前測量和校正帶來很大困難,從而給天文觀測、激光通訊、激光武器等眾多的工程應用帶來挑戰(zhàn)。為了提高自適應光學系統(tǒng)的校正能力,有必要對激光大氣傳輸中的相位奇點演化特性展開研究。中心光強為零且攜帶有相位奇點的渦旋光束因其特有的性質受到人們的廣泛關注。當渦旋光束在湍流大氣中傳輸時,傳輸介質會引起光強起伏、光束擴展以及光學渦旋的漂移等。另外,渦旋光束的拓撲荷可以作為信息的載體用于自由空間光通信中。因此,有必要研究渦旋光束在湍流大氣中的光強分布、光束擴展以及光學渦旋的演化特性等。本論文首先研究了激光在大氣中水平、斜程、上行和下行傳輸時,受湍流擾動的畸變光場中產(chǎn)生的相位奇點的演化特征;然后以拉蓋爾-高斯渦旋光束為例,系統(tǒng)研究了渦旋光束在湍流大氣中傳輸時的光強分布、光束擴展、渦旋光束拓撲荷的確定和光學渦旋的漂移等傳輸特性;最后簡單探討了無衍射貝塞爾光束在湍流大氣中的束寬擴展和相位奇點數(shù)密度的變化特性。主要研究內容和結論如下:1.數(shù)值模擬了激光在大氣中傳輸時,受湍流擾動的畸變光場中產(chǎn)生的相位奇點的演化特征。模擬結果顯示,相位奇點會成對產(chǎn)生;極性相反的相位奇點對會隨著波前向前傳播;相位奇點對的相對位置和間距在傳播過程中會發(fā)生變化;相位奇點也會成對地湮滅。2.數(shù)值模擬了激光在湍流大氣中水平傳輸時產(chǎn)生的相位奇點數(shù)密度與湍流效應特征參數(shù)的關系,這些參數(shù)包括傳輸距離,湍流強度,激光波長、湍流內尺度和外尺度等。計算結果表明,當其他傳輸條件一定時,相位奇點數(shù)密度分別隨傳輸距離的增加和湍流強度的增強而增加,隨湍流內尺度和激光波長的增加而降低;而相位奇點數(shù)密度基本不受湍流外尺度的影響。3.數(shù)值模擬了激光在湍流大氣中水平傳輸時兩種傳輸條件下的相位奇點數(shù)密度的變化過程。一種是湍流較弱但傳輸距離很長;另一種是傳輸距離較短但湍流很強,這兩種情況下均能產(chǎn)生強湍流效應。結果表明,湍流強度對相位奇點數(shù)密度的影響要大于傳輸距離對相位奇點數(shù)密度的影響;不同傳輸條件下產(chǎn)生的相位奇點數(shù)密度隨Rytov指數(shù)的變化過程有所不同,但它們之間的關系比較符合Logistic統(tǒng)計公式。4.模擬了激光在湍流大氣中自地面向空中垂直上行傳輸時畸變光場中出現(xiàn)的相位奇點數(shù)密度隨傳輸高度的變化過程。在傳輸高度一定的情況下,主要模擬了兩種激光傳輸過程:一種是固定發(fā)射激光的波長,變化傳輸路徑中的湍流強度;另一種是固定傳輸路徑中的湍流強度,變化發(fā)射激光的波長。結果表明,相位奇點數(shù)密度隨傳輸高度的增加其變化過程可以分成四個不同的區(qū)域;當發(fā)射激光的波長一定時,近地面處的湍流強度不同對應的相位奇點數(shù)密度達到峰值時的傳輸高度也是不同的,湍流越強,相位奇點數(shù)密度的峰值越高,其對應的傳輸高度卻越低;當湍流強度的分布一定時,畸變光場中的相位奇點數(shù)密度達到峰值時對應的傳輸高度基本不受激光波長的影響。另外,通過對模擬結果的曲線擬合發(fā)現(xiàn),不同條件下的相位奇點數(shù)密度隨傳輸高度的變化關系非常類似于黑體輻射公式。5.模擬了激光在湍流大氣中自地面向空中斜程傳輸時,相位奇點數(shù)密度的變化特征。結果表明,斜程傳輸時的相位奇點數(shù)密度隨傳輸距離的變化過程非常類似于上行傳輸時相位奇點數(shù)密度隨傳輸高度的變化過程;固定近地面處的湍流強度,當傳輸距離一定時,光束的發(fā)射天頂角越大,畸變光場中出現(xiàn)的相位奇點數(shù)密度越大且相位奇點數(shù)密度達到極大值時對應的傳輸距離越長;當發(fā)射天頂角和傳輸距離一定時,近地面處的湍流強度越強,畸變光場中產(chǎn)生的相位奇點數(shù)密度越大。6.模擬了激光在湍流大氣中自空中某一高度垂直下行傳輸至地面時,畸變光場中產(chǎn)生的相位奇點數(shù)密度的變化特征。結果表明,光源位置距離地面越高,在較高位置處的畸變光場中就會有相位奇點產(chǎn)生,且到達地平面處時的畸變光場中產(chǎn)生的相位奇點數(shù)密度越大;相位奇點數(shù)密度隨高度的降低而單調增加且在接近地平面處達到最大值。7.以拉蓋爾—高斯(LG)光束為例,模擬了渦旋光束在湍流大氣中傳輸時在垂直于傳輸方向的平面內的光強分布。結果表明:當渦旋光束在湍流大氣中傳輸時,光強由最初的中空光束演變?yōu)槠巾敼馐?并最終在遠場演變?yōu)楦咚构馐�。光強廓線的演變過程以及相位奇異性的消失與傳輸距離、湍流強弱、湍流外尺度、渦旋光束拓撲荷數(shù)、光束的束腰寬度以及光束的波長有關,而與湍流的內尺度無關。對于同一渦旋光束,傳輸距離越遠、湍流越強以及湍流外尺度越大,光強分布受到的影響越大。對于不同的渦旋光束,拓撲荷數(shù)越高、束腰越窄以及波長越長,光強分布受到的影響越小,在湍流大氣中越易于保持其原有的光強和相位分布特性。8.數(shù)值模擬了大氣湍流對渦旋光束束寬擴展的影響。結果表明:傳輸距離越長或湍流越強,渦旋光束在湍流大氣中傳輸時的束寬擴展受湍流的影響越大;渦旋光束的拓撲荷數(shù)越高、光束的束腰越小或光波的波長越長,束寬擴展受大氣湍流的影響反而越小;隨著湍流內尺度的減小或湍流外尺度的增加,大氣湍流對光束擴展的影響會有所增加,但影響幅度相對較小。另外,還比較了渦旋光束和普通高斯光束因湍流引起的光束擴展的差異。結果表明大氣湍流對普通高斯光束束寬擴展的影響要大于對渦旋光束束寬擴展的影響。9.通過數(shù)值分析接收面內相位奇點拓撲荷的代數(shù)和(簡稱為AS-PS),得出AS-PS近似等于入射渦旋光束拓撲荷的結論。提出了一種在湍流大氣中確定渦旋光束拓撲荷的方法——相位奇點代數(shù)和法。該方法可以有效的消除湍流的影響并減小確定拓撲荷的誤差。研究了傳輸參量、光束參量以及探測系統(tǒng)的口徑等對確定AS-PS的影響。結果表明:渦旋光束在湍流大氣中的傳輸距離越短、湍流強度越弱、入射渦旋光束的拓撲荷越低,利用該方法確定渦旋光束拓撲荷的標準偏差越小;合理選擇渦旋光束的束腰也會增加該方法的準確性;探測口徑近似等于渦旋光束傳輸至探測面上的主光斑尺寸時,相位奇點代數(shù)和與入射渦旋光束拓撲荷的相對誤差最小,該結論可以給探測器口徑的定量設計提供一定的參考依據(jù)。10.通過模擬光學渦旋在接收面的不同位置出現(xiàn)的頻次研究了湍流大氣中光學渦旋的漂移特性。由模擬結果可知,光學渦旋在接收面的不同位置出現(xiàn)的頻次或概率滿足高斯分布。隨著傳輸距離的增加、湍流的增強或入射渦旋光束拓撲荷的增加,光學渦旋位置的統(tǒng)計特性不再滿足高斯分布。另外,適當選擇入射渦旋光束的束腰會減小光學渦旋的漂移。以上這些結論可以為渦旋光束在自由空間光通訊中的應用提供一定的參考依據(jù)。11.初步探討了貝塞爾光束在湍流大氣中傳輸時引起的束寬擴展和相位奇點數(shù)密度的變化特性。結果表明,與零階貝塞爾光束和零階貝塞爾—高斯光束相比,貝塞爾—高斯渦旋光束由大氣湍流引起的束寬擴展程度最小且在一定條件自身所攜帶的光學渦旋基本不受湍流的影響,即貝塞爾渦旋光束更適用于自由空間光通信中信息的載體。
[Abstract]:Laser propagation in turbulent atmosphere, the amplitude and phase of light will lead to random fluctuations, receiving plane light field intensity fluctuation and phase distortion. In effect under the condition of strong turbulence, there will be some distortion intensity is zero and phase uncertain point light field, these points are called phase singularities. There is a phase singularity which brings great difficulties to the traditional adaptive optics wavefront measurement and correction to the astronomical observations, laser communication, laser weapon engineering and many other challenges. In order to improve the correction capability of adaptive optical system, it is necessary on the evolution properties of phase singularities of laser transmission in the atmosphere is studied. The intensity of the vortex center beam zero and carrying phase singularities have attracted extensive attention due to its unique properties. When the vortex beam propagation in turbulent atmosphere, the transmission medium will cause the intensity fluctuation Well, the beam spreading optical vortex drift. In addition, the topological charge of vortex beam can be used as the carrier of information for free space optical communication. Therefore, it is necessary to intensity distribution in the turbulent atmosphere of vortex beam, beam propagation and optical vortex evolution characteristics. This paper studied the laser level in the atmosphere in the slant, the uplink and downlink transmission, the evolution characteristics of light field distortion in phase singularities by turbulence perturbation; then the Laguerre Gauss vortex beam as an example, the light intensity distribution of vortex beams in atmospheric turbulence is studied systematically on the beam spreading, transmission characteristics and determine the topology of optical vortex vortex beam bearing the drift; finally discusses the characteristics of non diffraction Bessel beam in turbulent atmosphere beam width extension and phase number of singular points density. The main research contents and conclusions are as follows 1.: the numerical simulation of laser propagation in atmosphere, the evolution characteristics of light field distortion in phase singularities by turbulence disturbance. The simulation results show that the phase singularities will be produced in pairs; the opposite polarity of phase singularities with wavefront propagates; phase singularities of the relative position and distance change in communication in the process of relationship; phase singularities will pair annihilation.2. numerical simulation of the laser generated in a turbulent atmosphere, the odd number phase density and turbulence parameters, these parameters include the transmission distance, turbulence intensity, laser wavelength, turbulence inner scale and outer scale. The calculation results show that when the other transmission conditions when a certain number of singular points respectively with increasing phase density and turbulence intensity of the transmission distance increased, and decreased with increasing turbulence inner scale and laser wavelength; and the number of dense phase singularities The degree is not affected by the outer scale of turbulence numerical simulation of the effect of.3. laser in horizontal turbulent atmosphere, changes of two kinds of transmission under the condition of the phase number of singular points density. One is the weak turbulence but the transmission distance is very long; the other is a short transmission distance but the turbulence is very strong, these two kinds of situations can produce strong turbulence effect. The results show that the influence of turbulence intensity on the phase density is greater than the number of singular points affect the transmission distance of the phase change process of the odd number density; different transmission conditions of phase number of singular points density with Rytov index is different, but the relationship between them is consistent with the Logistic statistical formula.4. to simulate the change with the height of the process of laser transmission in atmospheric turbulence from the ground to the air vertical upward distortion in the light field transmission phase. When the number of singular points density transmission height, main mode The two laser transmission process: one is the fixed laser wavelength, the turbulence intensity change of the transmission path; the other is a fixed transmission path in turbulence intensity, changes in emission wavelength of the laser. The results show that the phase number of singular points density with the increase of the height of the transmission process can be divided into four different when the wavelength of the laser emission region; when the transmission of near ground surface turbulence intensity corresponding to the different phase of odd points density peak height is different, the stronger the turbulence is, the peak phase number of singular points density is higher, the corresponding transmission height is lower; when the turbulence intensity distribution at the corresponding transmission in distorted optical field phase singular points density peak height was not affected by the wavelength of the laser. In addition, the curve fitting of the simulation results showed that under different conditions of phase singular points density With the change of the height of the transmission relationship is very similar to the blackbody radiation formula.5. simulation of laser beam propagation in turbulent atmosphere from the ground to the air oblique propagation, phase change characteristics of odd points density. The results show that the oblique propagation of phase singular points density change with the transmission distance of the process is very similar to the uplink transmission phase odd the number density changes with the height of the transmission process; the turbulence intensity is fixed near the ground, when the transmission distance, the beam emission zenith angle increases, appear distorted optical field phase in the odd points greater density and phase singularity density reached the maximum when the corresponding transmission distance is longer; when the zenith angle of emission and the transmission distance, turbulence intensity near the ground surface is stronger, the distortion of light field phase in the number of singular points higher density.6. simulation of laser beam propagation in turbulent air from a vertical downward transmission To the ground when the number of singular points density variation of phase distortion in the light field. The results show that the position of the light source from the ground is higher in the high position of the distorted optical field will produce phase singularities, the distortion of phase singularities in the light field density and arrived at the plane of the larger phase; the odd points density with height decrease monotonously increased and near the ground plane reaches a maximum at.7. (LG) with Laguerre Gauss beam as an example, the simulation of the vortex beams in atmospheric turbulence intensity in the plane perpendicular to the direction of transmission in distribution. The results show that when the vortex beam propagating in turbulent atmosphere when the light intensity changes from the original hollow beam of flat topped beam, and eventually evolved into the Gauss beam in the far field. The evolution of intensity profile and the phase singularity and the disappearance of the transmission distance, turbulence intensity, turbulent outer scale vortex. Optical beam topological number, the beam waist width and beam wavelength, and has nothing to do with the inner scale of turbulence. For the same vortex beam, the transmission distance is far more turbulent intensity and turbulent outer scale is larger, the greater the effect of light intensity distribution. For different vortex beam, the topological charge of the high waist is narrow and the longer wavelength, the intensity distribution of the effect is small, easy to maintain its original intensity and phase distribution of.8. numerical influence of atmospheric turbulence on the vortex beam width spreading in a turbulent atmosphere were simulated. The results show that the transmission distance is longer or more strong turbulence, vortex beams propagating in in the turbulent atmosphere when the beam width is more affected by turbulence; topological charge of vortex beam with higher beam waists smaller or longer wavelength, the beam width extension affected by atmospheric turbulence decreases with the turbulence inner scale; Increase or the decrease of the outer scale of turbulence, the influence of atmospheric turbulence on the beam spreading will increase, but the influence is relatively small. In addition, also compared the difference of beam vortex beams and ordinary Gauss beam due to turbulence induced expansion. The results show that the influence of atmospheric turbulence on the ordinary Gauss beam width spreading is greater than the expansion of the vortex the beam width effect of.9. through numerical analysis of in-plane phase singularities receiving algebraic and topological charge (referred to as AS-PS), the AS-PS is approximately equal to the topological charge of the vortex beam incident. The conclusion presents a method of determining the topology in the atmospheric turbulence vortex beam bearing - phase singularities and algebraic method. This method can be effective to eliminate the effects of turbulence and reduce the error of determining the topological charge. The transmission parameters are investigated, and the effects of the beam parameters detection system to determine the diameter of AS-PS. The results show that the vortex The propagation distance in the turbulent atmosphere is shorter, the turbulence intensity is weaker, the topological charge of vortex beam incidence is low, determine the standard deviation of the topology of vortex beam bearing using this method; reasonable choice of vortex beam waist will also increase the accuracy of the method; detection aperture is approximately equal to the spot size of vortex beam transmitted to the main on the surface of the probe, and the relative error of phase singularities of algebraic and topological charge of the vortex beam incident is minimum, the conclusion can give the quantitative design of detector aperture and provided a reference for the.10. simulation of optical vortex research in receiving the different position of the frequency drift characteristics of the optical vortex in a turbulent atmosphere. From the simulation results the frequency, or probability of optical vortex in different position of the receiving surface satisfies Gauss distribution. With the increase of the transmission distance, enhanced or incident optical vortex turbulence Increase the beam topological charge, the statistical properties of the optical vortex position no longer satisfies Gauss distribution. In addition, will reduce the incidence of optical vortex vortex beam waist appropriate selection drift. These conclusions can be used as vortex beams in free space optical communication to provide a reference for.11. discussed the characteristic changes caused by Bessel beam transmission in the turbulent atmosphere when the beam width extension and phase number of singular points density. The results show that, compared with the zero order Bessel beam and zero order Bessel Gauss beams, Bessel - Gauss vortex beams by atmospheric turbulence caused by the beam width of the optical vortex and its extended degree minimum carried under certain conditions is not affected by turbulence the carrier, namely Bessel vortex beam is more suitable for the information of free space optical communication.

【學位授予單位】：山東師范大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：TN24

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