OPTIMAL BEAM FORMING FOR LASER BEAM PROPAGATION ...

More documents

Recommendations

Info

Historically, most of the original work on optical propagation deals withuniform plane or spherical waves. Recently, however, the propagation of otherbeams, such as truncated Gaussian beams, through random media have beenwidely studied [47]. But the problem of what type of optical beam profile willperform better through random media is seldom studied. By saying “performbetter”, we mean that the optical beam is less sensitive to turbulence effectssuch as beam spreading and scintillation. To be more precise, specific criteriaare needed to evaluate the beam performance.In this research, we will study the statistical properties of the opticalbeams after propagation through turbulent media. The effects of both sourcecoherence and random media are investigated. The goal of this research is tocompensate the random media effects in beam propagation by changing thetransmitted optical fields or choosing the optical source coherence for certainperformance metrics. Compensated beams are expected to concentrate morepower in the target region or reduce the beam scintillation effectively.In the study of the optimal beam to maximize the weighted integrated intensity,we derive a similarity relationship between pupil-plane phase screenand extended Huygens-Fresnel model, and demonstrate the limited utilityof maximizing the average integrated intensity. In the study of the optimalbeam to minimize the scintillation index, we derive the first- and second-ordermoments for the integrated intensity of multiple coherent modes. Hermite-Gaussian and Laguerre-Gaussian modes are used as the coherent modes tosynthesize an optimal partially coherent beam. The optimal beams demon-6
strate evident reduction of scintillation index, and prove to be insensitive tothe aperture averaging effect.1.3 Dissertation OrganizationThe rest of this dissertation is organized as follows.In Chapter 2, I willdescribe the background of laser beam propagation through random media.Mathematic models of beam propagation, statistical random media, and optimizationcriterions are introduced in Chapter 3.The optimal beams tomaximize the concentrated power and to minimize the scintillation index areinvestigated in Chapter 4 and Chapter 5 respectively. A summary and theconclusions of this research are given in Chapter 6.7
Page 5 and 6: AcknowledgementFirst and foremost,
Page 7 and 8: 3.2.1 Paraxial waves and Gaussian b
Page 9 and 10: 6 Summary 996.1 Conclusions . . . .
Page 11 and 12: 4.2 Airy pattern: (a)Normalized Air
Page 13 and 14: 5.9 Monte-Carlo simulation by trans
Page 15 and 16: List of Tables4.1 Physical paramete
Page 17 and 18: Chapter 1Introduction1.1 Motivation
Page 19 and 20: eam due to turbulent media can, how
Page 21: the effects of refraction and diffr
Page 25 and 26: are the most important causes of al
Page 27 and 28: mal blooming can be ignored and the
Page 29 and 30: centroid is caused by large eddies
Page 31 and 32: optics systems for laser beam contr
Page 33 and 34: YYouXθvXAZZ = 0Z = dFigure 3.1: Th
Page 35 and 36: When the propagation distance d is
Page 37 and 38: wherew(z) = w 0[1 +( zz 0) 2] 1/2,
Page 39 and 40: Figure 3.2: Hermite Gaussian beams
Page 41 and 42: 3.3 Optical CoherenceThe optical co
Page 43 and 44: where F (⃗r, ν) is the Fourier t
Page 45 and 46: from finite surfaces with small dif
Page 47 and 48: 3.4.1 Kolmogorov turbulence modelKo
Page 49 and 50: structure function of refractive in
Page 51 and 52: The wave number k(⃗r) can be expr
Page 53 and 54: An iterative method can then be tak
Page 55 and 56: We then get( ) aψ s (⃗r) = χ +
Page 57 and 58: It can be seen that the ensemble av
Page 59 and 60: 3.6.1 Maximization of the integrate
Page 61 and 62: Chapter 4Optimal Beam to Maximize t
Page 63 and 64: A with aperture function⎧⎪⎨ 1
Page 65 and 66: 4.1 Optimal Beam in Free SpaceThe m
Page 67 and 68: −0.132.5−0.052u’ (meter)01.51
Page 69 and 70: plane as∫ z+∆zφ(⃗u) = k n(
Page 71 and 72: −0.132.5−0.052u’ (meter)00.05
Page 73 and 74:
formh(⃗v, ⃗u) = 1 (jλd exp j 2
Page 75 and 76:
The transverse coherence length has
Page 77 and 78:
models - extended Heygens-Fresnel p
Page 79 and 80:
21.8free spaceturbulence10.91.60.81
Page 81 and 82:
2.5free spaceturbulence10.920.80.71
Page 83 and 84:
Chapter 5Optimal Beam to Minimize t
Page 85 and 86:
and the corresponding received inte
Page 87 and 88:
following two sections, we will dis
Page 89 and 90:
where Γ(⃗u 1 , ⃗u 2 ) = 〈φ(
Page 91 and 92:
intensity can be expressed as∫∫
Page 93 and 94:
5.4 Selection of coherent modesThe
Page 95 and 96:
m = 0m = 1m = 2222000−2−2−2
Page 97 and 98:
Scintillation Index0.140.130.120.11
Page 99 and 100:
p = 0p = 1p = 2420−2420−2420−
Page 101 and 102:
N 1 2 3 4 5 6 7 8α 0 1.0000 0.1177
Page 103 and 104:
120100TheoreticalSimulation1.21Theo
Page 105 and 106:
Scintillation Index0.40.350.30.250.
Page 107 and 108:
Scintillation index of single mode0
Page 109 and 110:
0.90.80.7r 0= 0.05 mr 0= 0.1 mr 0=
Page 111 and 112:
0.6C n2 = 2x10−16C n2 = 5x10−16
Page 113 and 114:
known fact that planets scintillate
Page 115 and 116:
Chapter 6Summary6.1 ConclusionsIn t
Page 117 and 118:
showed that increasing the receiver
Page 119 and 120:
L m p (x) Laguerre polynomialn Inde
Page 121 and 122:
Bibliography[1] L. C. Andrews and R
Page 123 and 124:
[18] D. deWolf. Strong irradiance f
Page 125 and 126:
[36] A. Ishimaru. Flucturations of
Page 127 and 128:
[54] C. Primmerman and D. Fouche. T
Page 129 and 130:
[73] V. I. Tatarski. Waves Propagat
show all

OPTIMAL BEAM FORMING FOR LASER BEAM PROPAGATION ...

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?