The growth and saturation characteristics of stimulated Brillouin scattering (SBS) in the interaction of an intense (Ｉ≤ 10¹³ W/cm²) CO₂ laser beam with an underdense plasma are investigated experimentally. The plasma is produced by focussing a short (2 ns FWHM), CO₂ laser pulse onto a stabilized nitrogen gas jet which flows from a Laval nozzle into low pressure helium. The resulting SBS interaction is studied through observations of the intensity and spectral behavior of the backscattered light as well as through temporally resolved ruby laser Thomson scattering measurements of the spatial and spectral behavior of the SBS generated ion acoustic waves. SBS occurs primarily in the long scale length, low density plasma located in the background gas in front of the jet. Initially, the instability grows absolutely at a rate within a factor of two of the predicted temporal growth rate. The SBS reflectivity is observed to saturate at less than 10%. This low reflectivity is a result of two processes. First, the SBS interaction region and the associated ion acoustic waves are broken up into several smaller regions, hence limiting the coherence length of the waves, and second, the ion acoustic fluctuation amplitude saturates at less than 20%. The latter saturation is attributed to trapping of ions within the potential troughs of the ion acoustic waves. The observed occurrence of the first harmonic in the ion acoustic wave spectrum as well as temporal modulations in the wave amplitude and sidebands in the spectrum of the backscattered light can be explained as consequences of the ion trapping. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The goal of this dissertation has been to develop techniques in order to use Brillouin spectroscopy as a tool for studying the elastic properties of thin films on a scale of ≃100 Å. In order to develop that capability we have built a tandem multi-pass Fabry-Perot interferometer, and that interferometer was used to study the elastic properties of Langmuir-Blodgett films. These films were chosen because they can be deposited one molecular layer at a time. As a result of these investigations we have measured the density and elastic constants of the Langmuir-Blodgett film cadmium arachidate. Samples of cadmium arachidate were prepared on molybdenum and BK-7 glass substrates. Data were accumulated for a range of thicknesses and for different scattering geometries. These data will be used to argue that guided acoustic waves were observed in a highly anisotropic film. The observed guided acoustic waves will be identified as a Rayleigh wave and a tight band of Sezawa modes. No Love modes were detected in these experiments; however, evidence for reorientational modes typical of anisotropic liquids was detected. The dispersion of the Rayleigh wave as a function of thickness together with thick film scattering data were used to estimate the elastic constants in cadmium arachidate. In particular the shear elastic constant c₄₄ was found to be a small value: c₄₄ < 4.0x10⁸ N/m². The remaining elastic constants were estimated, assuming hexagonal film symmetry, to be c₆₆ < 4.5x10⁹ N/m², C₁₁ ≃ 1.1x10¹⁰ N/m², c₃₃ ≃ 2.1x10¹⁰ N/m², c₁₃ ≃ 1.0x10¹⁰ N/m², and c₁₂ > 3.x10¹⁰ N/m². It is interesting to note that the acoustical behavior of cadmium arachidate is quite similar to the smectic phase liquid crystals (c₄₄ = 0).

Thesis (Ph. D.)--Lehigh University, 2000. / Includes bibliographical references and vita.

No description available.

Copies of author's previously published articles inserted. / Includes bibliographical references. / viii, 162, [9] leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / A study of stimulated Brillouin scattering and its use for correcting phase aberrations in laser oscillators. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 1998

Copies of author's previously published works inserted. / Bibliography: p. 119-127. / 12, 127, [8], 35 p., [3] leaves : ill. (chiefly col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This thesis demonstrates the combined use of stimulated Brillouin scattering (SBS) for aberration correction, auto alignment and pulse compression as an ideal technology for studies of nonlinear optical processes, in particular nonlinear optical scattering (NLS). / Thesis (Ph.D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 1998

Thesis (Ph.D.) -- University of Adelaide, Dept. of Physics and Mathematical Physics, 1998. / Copies of author's previously published works inserted. Bibliography: p. 119-127.

Copies of author's previously published works inserted. Bibliography: p. 119-127. This thesis demonstrates the combined use of stimulated Brillouin scattering (SBS) for aberration correction, auto alignment and pulse compression as an ideal technology for studies of nonlinear optical processes, in particular nonlinear optical scattering (NLS).

Acoustic modes guided by thin-film metal superlattices have been investigated using Brillouin spectroscopy. Samples were grown on both single-crystal sapphire and fused silica substrates by alternately sputtering two different metals to yield a total thickness in the range 0.3 - 0.5 μm. Structural and chemical characterization of the polycrystalline films was performed using x-ray diffraction. Rutherford backscattering and optical interferometry. Thermally excited acoustic waves in the metal film create a surface ripple which weakly interacts with light incident from a single mode argon laser. A tandem Fabry-Perot consisting of two synchronized 3-pass cavities is used to measure the frequency shift of light which is inelastically scattered from acoustic waves. The contrast ratio of this interferometer exceeds 10¹⁰ and provides sufficient stray light rejection to detect the surface Rayleigh wave and as many as 13 higher order acoustic modes. The elastic stiffness constants of the anisotropic superlattices were estimated by fitting the measured acoustic mode velocities to a parameterized acoustic model. A comparison is made between these elastic constants and those predicted from the properties of the separate bulk constituents. The dependence of bilayer wavelength on the elastic properties of both Cu/Nb and Mo/Ta superlattices over the range of roughly 10 to 200 Å was determined. The unexpected softening of Cu/Nb superlattices within a range of bilayer wavelengths near 20 Å which was reported previously is qualitatively similar to the measurements reported here. It is shown that the elastic stiffness coefficient with the largest variation is c₄₄. The stiffness variations determined for the Mo/Ta samples are much smaller than for Cu/Nb. It is suggested that this is due to either structural differences (Cu/Nb is fcc-bcc and Mo/Ta is bcc-bcc) or the smaller interfacial lattice mismatch for Mo/Ta. Interfacial strain is found to be strongly correlated with the stiffness variations of the Mo/Ta samples. However, the underlying cause of these variations in stiffness remains anomalous. This dissertation also reports the first observations of Love waves and Stoneley waves by Brillouin scattering. The purely transverse Love waves guided by Cu/Nb films were detected by elasto-optic scattering from the evanescent acoustic strain in the sapphire substrate. The stiffness coefficient c₁₂ of the hexagonally symmetric metal film cannot be determined by the other guided acoustic waves which ripple the surface. Molybdenum in contact with fused silica is predicted to support a Stoneley wave which is guided by the interface. The lowest order Sezawa made guided by a molybdenum film was found to evolve to the Stoneley wave as the film becomes thicker. These measurements together with measurements of the surface Rayleigh wave show that the stiffness of the sputtered metal films is quite homogeneous and independent of film thickness.

基於光纖非線性效應的光學信號處理在光纖通信和傳感中起著重要作用。在各種非線性效應中，光纖中的布里淵散射不僅被廣泛應用於高速通信信號的處理，而且被用於建立光纖傳感器。本文研究基於布里淵散射的光學信號處理新技術在光通信和傳感中的應用。 / 近年來由於慢光技術在實現時間延遲和光學信號處理中的廣泛應用，它吸引了廣泛的注意力。 在各種實現慢光的技術中，基於布里淵散射的慢光技術展示了很大的潛力，因為它具有在常溫工作以及與現有光纖系統兼容的優勢。但是由於布里淵泵浦和信號之間嚴格的頻率要求，大多數的研究工作是建立於一個泵浦延遲一個信號的基礎上，所以只能獲得一個被延遲的信道。本文提出了一種在一個布里淵泵浦的慢光系統中實現同時產生多個延遲信號的技術。這種技術應用了基於四波混頻的廣播效應。輸入信號被布里淵泵浦延遲的同時，延遲通過三個四波混頻泵浦的廣播效應傳遞給其他六個新產生的信道。這種慢光廣播技術可以被應用於並行光學信號處理，比如實現多信道同步以及時分複用。 / 光纖傳感技術為結構的健康提供了一種優秀的監測方法，尤其是溫度和應力的監測。在過去的二十年間，基於布里淵散射的傳感技術吸引了大批人的興趣，因為布里淵光纖傳感器擁有高分辨率，長距離監測以及監測範圍廣的優點。本文提出了一種新的基於布里淵慢光的溫度和應力傳感技術。布里淵頻移的溫度和應力相關性使得輸入光脉衝的延遲也與溫度和應力相關，因此我們通過測量這個延遲來監測溫度和應力。我們分別實現了對100米和2米單模光纖的溫度測量。隨後我們也實現了分佈式溫度和應力監測。通過設置泵浦和探測光脉衝之間的延遲時間，我們可以監測特定位置的光纖。因此，通過控制整個延遲時間，我們實現了對整個光纖的溫度和應力分佈的監測。相比于普通的布里淵光纖傳感器，我們這種技術擁有以下優點：更加直接簡單的實現監測，快速的反應時間以及實時監測的潛力。 / 波長轉換在路由和交換中起了很重要的作用。在各種波長轉換的技術中，基於四波混頻的波長轉換非常優越因為它具有對調製格式，比特率以及通信協議透明的優點。但是，四波混頻只有在各個光波的相速度匹配的情況下才能有效的產生。這種匹配條件很難在一個很寬的頻段內保持，因此四波混頻的轉換帶寬是很有限的。本文提出了一種基於零增益受激布里淵散射的方法來動態地控制四波混頻的相位匹配。 通過布里淵泵浦和斯托克斯光引入自我補償的受激布里淵增益和損耗，四波混頻的相位匹配條件可以被受激布里淵散射激發的折射率改變來靈活的控制，並且不會影響四波混頻初始的參數。我們把這種零增益受激布里淵散射應用于增大簡並四波混頻的帶寬，增強通信信息波長轉換的效果，全光調控非簡並四波混頻的帶寬，實現偏振不敏感寬帶波長轉換以及延長基於四波混頻波長轉換和色散的延遲線的最大延遲時間。 / 低噪聲寬帶放大可以通過光學參量過程來實現。雖然光參量放大器可以提供高至70分貝的增益，但是這種參量放大器經常受限於各個光波的相位不匹配。在本文中，我們把零增益受激布里淵散射用於光參量放大器來動態的控制它的增益譜。基於這種技術，我們動態地改變了傳統的“M“型增益譜，並且由此得到了非常平滑的增益譜，增益的變換量僅僅在0.1分貝以內。 / Optical signal processing based on fiber nonlinearities plays an important role in both fiber-optic communications and sensing. Among various nonlinear effects, stimulated Brillouin scattering (SBS) in optical fibers has been widely employed not only in processing of high-speed communication signals, but also in constructing fiber-optic sensors. This thesis investigates new techniques of optical signal processing based on SBS for fiber-optic communications and sensing. / In the recent years, slow light has attracted considerable interest because of its numerous applications, in realizing variable true time delay and in optical information processing. Among various slow light mechanisms, the SBS based slow light shows great potential in all-optical signal processing due to the advantages of room-temperature operation and device compatibility with existing fiber systems. However, owing to the tight requirement of spectral alignment between the SBS pump and the signal, most of the published works are for the case where one SBS pump is used to delay a single channel. Hence, only one delayed channel is obtained. In this thesis, we demonstrate a technique to simultaneously generate multiple delayed signals through four-wave mixing (FWM) wavelength multicasting in a single-pump stimulated Brillouin scattering (SBS) based slow light system. The signal delay is achieved with a SBS pump while at the same time the delay is transferred to six other channels by three FWM pumps employed for wavelength multicasting. This slow light multicasting technique may find applications in parallel optical information processing such as simultaneous multichannel synchronization and time division multiplexing. / Fiber-optic sensor techniques provide a promising approach for structure health monitoring, especially the temperature and strain monitoring. The technique based on Brillouin scattering has attracted much interest in the past two decades because Brillouin fiber sensors offer advantages of high resolution, long distance sensing, and large sensing range. In the thesis, we propose and experimentally demonstrate a new method for temperature/strain sensing using stimulated Brillouin scattering based slow light. The approach relies on temperature/strain dependence of the Brillouin frequency shift in a fiber, hence the time delay of an input probe pulse. By measuring the delay, temperature/strain sensing can be realized. We achieve temperature measurement for both a 100 m single mode fiber (SMF) and a 2 m SMF. Distributed temperature/strain sensing has been demonstrated later. The temperature/strain of a particular fiber section can be monitored by setting an appropriate relative delay between the pump and probe pulses. By controlling the relative delay, we have achieved distributed profiling of the temperature/strain along the whole sensing fiber. Compared to conventional Brillouin fiber sensors, our scheme has the merits of more straightforward implementation, fast response and potential of real-time monitoring. / Wavelength conversion plays an important role in wavelength routing and switching. Among various schemes for wavelength conversion, the one based on FWM is superior as it offers advantages in being transparent to modulation formats, bit-rates, and communication protocols. However, significant FWM can occur only if the phase velocities of the interplaying waves are matched. The matching condition can hardly be satisfied over a wide spectral range and hence the conversion bandwidth is often limited. In this thesis, we propose and experimentally demonstrate an approach to dynamically control the FWM phase matching condition by using gain-transparent SBS. By introducing self-compensation of optical gain/loss with SBS pump and Stokes waves, the FWM phase matching condition can be flexibly controlled through SBS induced refractive index change without affecting the initial parameters of the FWM. The gain-transparent scheme is employed to enlarge the degenerate FWM conversion bandwidth, enhance the performance in wavelength conversion of communication signals, all-optically manipulate non-degenerate FWM conversion bandwidth, achieve both polarization-insensitive and wideband operation in a dual orthogonal pump wavelength converter, and extend the maximum optical delay of a delay line based on FWM wavelength conversion and dispersion. / Low noise and broadband amplification are possible by using optical parametric processes. Although fiber-optic parametric amplifier (FOPA) can provide gain as high as 70 dB, its operation is often confined by phase mismatch of the interplaying fields. In this thesis, we apply gain-transparent SBS to a FOPA and dynamically control its gain profile. The conventional “M“ shape gain profile can be dynamically changed. Flattening of the gain profile to within 0.1 dB variation has been achieved. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Wang, Liang. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references. / Abstract also in Chinese. / ABSTRACT --- p.i / ACKNOWLEDGEMENT --- p.vi / TABLE OF CONTENT --- p.viii / Chapter 1 --- INTRODUCTION --- p.1 / Chapter 1.1 --- Overview of Optical Signal Processing --- p.3 / Chapter 1.2 --- Outline of the Thesis --- p.6 / References --- p.10 / Chapter 2 --- STIMULATED BRILLOUIN SCATTERING IN OPTICAL FIBERS --- p.15 / Chapter 2.1 --- Physical Process of Brillouin Scattering --- p.16 / Chapter 2.2 --- Stimulated Brillouin Scattering Under Steady-State Conditions --- p.19 / Chapter 2.3 --- The Brillouin Gain --- p.22 / Chapter 2.3.1 --- Complex Brillouin Gain --- p.22 / Chapter 2.3.2 --- Brillouin Gain Spectrum --- p.24 / Chapter 2.4 --- Threshold of Brillouin Scattering --- p.30 / References --- p.32 / Chapter 3 --- SLOW LIGHT BASED ON SBS IN OPTICAL FIBERS --- p.34 / Chapter 3.1 --- Introduction to Slow Light --- p.35 / Chapter 3.2 --- Slow Light based on SBS in Optical Fibers --- p.39 / Chapter 3.2.1 --- Mathematical Description --- p.39 / Chapter 3.2.2 --- Delay of Optical Signals by SBS based Slow Light --- p.42 / Chapter 3.3 --- Generation of Multichannel Delayed Pulses by FWM Assisted SBS Slow Light System --- p.46 / Chapter 3.3.1 --- Principle and Experimental Setup --- p.47 / Chapter 3.3.2 --- Results and Discussion --- p.51 / References --- p.58 / Chapter 4 --- SBS SLOW-LIGHT-BASED FIBER-OPTIC SENSOR --- p.64 / Chapter 4.1 --- Introduction to Fiber-Optic Sensors --- p.66 / Chapter 4.2 --- Principle of Fiber-Optic Sensor based on SBS Slow Light --- p.69 / Chapter 4.3 --- Temperature Sensing by SBS Slow Light for a Whole Segment of Fiber --- p.73 / Chapter 4.3.1 --- Temperature Sensing for a 100 m Single-Mode Fiber --- p.73 / Chapter 4.3.2 --- Temperature Sensing for a 2 m Single-Mode Fiber --- p.76 / Chapter References --- p.80 / Chapter 5 --- DISTRIBUTED TEMPERATURE & STRAIN SENSING USING SBS-BASED SLOW LIGHT --- p.82 / Chapter 5.1 --- Introduction to Distributed Brillouin Fiber Sensor --- p.84 / Chapter 5.2 --- Distributed Fiber-Optic Temperature Sensor Using SBS-based Slow Light --- p.91 / Chapter 5.2.1 --- Principle and Experimental Setup --- p.92 / Chapter 5.2.2 --- Results and Discussion --- p.94 / Chapter 5.3 --- Distributed Fiber-Optic Strain Sensor Using SBS-based Slow Light --- p.101 / Chapter 5.3.1 --- Principle and Experimental Setup --- p.101 / Chapter 5.3.2 --- Results and Discussion --- p.104 / References --- p.109 / Chapter 6 --- DYNAMIC CONTROL OF PHASE MATCHING IN FWM WAVELENGTH CONVERSION BY GAIN-TRANSPARENT SBS --- p.114 / Chapter 6.1 --- Phase-matching Condition in FWM --- p.116 / Chapter 6.2 --- Conversion Bandwidth Enlargement in Degenerate FWM Using Phase-Matching Control by Gain-Transparent SBS --- p.119 / Chapter 6.2.1 --- Principle and Experimental Setup --- p.120 / Chapter 6.2.2 --- Results and discussion --- p.125 / Chapter 6.3 --- Wavelength Conversion of Communication Signals Using Degenerate FWM with Gain-Transparent SBS for Phase-Matching Control --- p.131 / Chapter 6.3.1 --- Principle --- p.131 / Chapter 6.3.2 --- Wavelength Conversion for Amplitude-Modulated Signals --- p.133 / Chapter 6.3.3 --- Wavelength Conversion for Phase-Modulated Signals --- p.139 / Chapter 6.3.4 --- Discussion --- p.145 / Chapter 6.4 --- All-Optical Manipulation of Non-Degenerate FWM Conversion Bandwidth by Gain-Transparent SBS --- p.150 / Chapter 6.4.1 --- Principle and Experiment Setup --- p.151 / Chapter 6.4.2 --- Results and Discussion --- p.153 / Chapter 6.5 --- Enhanced Performance of Polarization-insensitive Wavelength Conversion through Dynamic Control of Optical Phase --- p.157 / Chapter 6.5.1 --- Principle and Experiment Setup --- p.157 / Chapter 6.5.2 --- Results and Discussion --- p.160 / Chapter 6.6 --- Extension of the Maximum Optical Delay using Gain-Transparent-SBS-Controlled FWM Wavelength Conversion and Group Velocity Dispersion --- p.165 / Chapter 6.6.1 --- Principle and Experiment Setup --- p.166 / Chapter 6.6.2 --- Results and Discussion --- p.169 / References --- p.174 / Chapter 7 --- DYNAMIC CONTROL OF GAIN PROFILE IN FIBER OPTICAL PARAMETRIC AMPLIFIER BY GAIN-TRANSPARENT SBS --- p.182 / Chapter 7.1 --- Introduction to FOPA --- p.184 / Chapter 7.2 --- Dynamic Gain Profile in FOPA Assisted by Gain-Transparent SBS --- p.187 / Chapter 7.2.1 --- Principle and Experimental Setup --- p.187 / Chapter 7.2.2 --- Results and Discussion --- p.190 / References --- p.196 / Chapter 8 --- THESIS SUMMARY AND FUTURE WORK --- p.200 / Chapter 8.1 --- Summary --- p.201 / Chapter 8.2 --- Future Work --- p.206 / References --- p.208 / APPENDICES --- p.i / Chapter Appendix A. --- List of Publications --- p.i / Chapter Appendix B. --- List of Figures --- p.iv