Includes bibliographical references (leaves 205-227) A study of phase conjugation by stimulated Brillouin scattering is presented with emphasis on the limiting factors, such as aperture and polarization losses, spatial coherence and saturation of the incident wave on the quality of phase conjugation, as well as the application of stimulated Brillouin scattering to loop phase-cojugated mirror and intracavity-SBS-cell-phase-conjugated oscillator.

Thesis (Ph.D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 2001. / Includes bibliographical references (leaves 205-227).

Random fiber lasers, a new type of fiber laser that uses disordered medium to provide distributed feedback, have drawn considerable interest in the photonics community over the past ten years. Stimulated Brillouin scattering (SBS), with a typical narrow spectral width of ~100 MHz, provides an important gain mechanism for random fiber lasers. Brillouin random fiber laser (BRFL) has shown excellent advantages in generating highly coherent photons and in ultrasound sensing. However, the accompanied large intensity noise in BRFLs hinders its further performance improvement and practical applications. In order to design a low noise BRFL, it is important to explore the fundamental physics behind BRFL and study its output characteristics. This thesis focuses on the study of random lasing mechanism in BRFL, which lays the foundation for the demonstration of a low noise BRFL. The main research results and contributions are as follows: (1) In order to understand the dynamic noise properties of BRFLs, the properties of the acoustic wave generated by BRFL, including its intrinsic spectral width, intensity dynamics, distributed spectrum and distributed intensity statistics are characterized for the first time. The characterization method is based on the SBS enhanced polarization decoupled four wave mixing process, where the pump wave, Stokes wave, probe wave and reflected probe wave are coupled through the fiber density variation induced by the acoustic wave. It is demonstrated that the intrinsic spectral width of the acoustic wave in the Brillouin gain fiber depends on the spectral convolution of pump light and Stokes light. Stochastic behaviour is introduced to the intensity dynamics of the acoustic wave when the linewidth of the pump light (or the Stokes light) is larger than several MHz. The distributed spectra of the dynamic grating are determined by the birefringence of the Brillouin gain fiber, which have maximum change on the order of 10-7 to 10-6 when the BRFL is on operation. Different proportion of optical rogue waves are detected at high gain position and low gain position near the lasing threshold, proving the nonlinear amplification of the SBS process. (2) In order to study the mode selection mechanism of the distributed random feedback and explore new physics phenomenon in BRFLs, the conventional Rayleigh scattering fiber in BRFL is replaced by the artificially controlled random scattering medium. First, weak FBG array with random spacing offers distributed feedback with varied length, which demonstrate the longitudinal mode filter function of the distributed random feedback. Single longitudinal mode operation of BRFL is realized by using appropriate length of the FBG array. Then, scattering from random fiber grating (RFG) with varied grating period is used to provide feedback for BRFL. The enhanced backscattering strength from RFG improves the slope efficiency of BRFL to 29.3% and reduces the lasing threshold to 10.2 mW. By calculating the correlation of the intensity fluctuation spectra from trace to trace, the correlation of two traces is found to be dependent on the specific two chosen traces, demonstrating the replica symmetry breaking phenomenon in photonics. (3) RFG with relatively large refractive index modulation shows potentials in improving the performance of the BRFL. In order to investigate the working mechanism of the RFG, optical frequency domain reflectometry (OFDR) with spatial resolution of 8 μm is employed to characterize the property of RFG. The backscattering strength and spectral response of RFG is highly related to the degree of randomness of RFG. Theoretically, entropy is introduced to build a quantitative relationship between the degree of randomness and backscattering strength of the RFG based on the transfer matrix method. A linear relationship between the average reflectivity of the RFG in dB scale and sub-grating’s entropy is found. Further, based on a polarization maintaining RFG, a low noise BRFL is proposed and demonstrated. Compared to Rayleigh scattering, the polarization maintaining RFG can tolerate environmental perturbation, leading to a 20 dB intensity noise suppression of the BRFL in the low frequency domain from 10 Hz to 1 kHz. (4) The dynamic properties of the slowly varying frequency drift of a dual-wavelength BRFL in polarization maintaining fiber are characterized. Two principal lasing peaks in each polarization are enabled by the combined distributed Rayleigh scattering and the Brillouin gain provided by the polarization maintaining fiber with large birefringence. Polarization dependent and polarization independent spectral variations are studied in the dual-wavelength BRFL due to the environmental perturbation and gain competition. The probability distribution of the lasing frequency exhibits a dip near the mean frequency that is caused by the spectral hole burning. By calculating the matrix of the Pearson correlation coefficient, the internal correlations between different part of random fiber laser spectra are found, which enhances the understanding of the fundamental physics of random lasing process.

by Pang Kam Moon. / Title also in Chinese characters. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1993. / Includes bibliographical references (leaves 120-121). / LIST OF FIGURES --- p.iv / ACKNOWLEDGEMENTS --- p.x / ABSTRACT --- p.xi / Chapter CHAPTER 1 --- INTRODUCTION --- p.1 / Chapter CHAPTER 2 --- SPONTANEOUS BRILLOUIN SCATTERING IN MICRODROPLETS --- p.10 / Chapter 2.1 --- Outline of the theory of Spontaneous Brillouin Scattering / Chapter 2.2 --- Low-Q Spontaneous Brillouin Scattering / Chapter 2.3 --- High-Q Spontaneous Brillouin Scattering / Chapter CHAPTER 3 --- FORMULATION AND RESULTS OF STEADY STATE SBS --- p.16 / Chapter 3.1 --- SBS in Extended and Spherical Media / Chapter 3.2 --- Formulation / Chapter 3.3 --- Monochromatic Plane Wave with Definite Helicity / Chapter 3.4 --- Lorentzian Approximation to J(z) / Chapter 3.5 --- Edge Illumination / Chapter CHAPTER 4 --- TRANSIENT EFFECTS ON INTERNAL INTENSITY --- p.56 / Chapter 4.1 --- Enhancements for Internal Intensity / Chapter 4.2 --- Formulation for Transient Incident Pulse Gaussian Profile / Chapter 4.3 --- Absorption Effects / Chapter CHAPTER 5 --- TRANSIENT STIMULATED BRILLOUIN SCATTERING --- p.74 / Chapter 5.1 --- Slowly Varying Phase and Amplitude Approximation / Chapter 5.2 --- Long Temporal Gaussian Profile Incident Light / Chapter 5.3 --- Short Temporal Gaussian Profile Incident Light / Chapter CHAPTER 6 --- SBS IN MICRODROPLETS WITH ABSORPTION --- p.82 / Chapter 6.1 --- Steady State SBS with Absorption / Chapter 6.2 --- Long Temporal Gaussian Profile Incident Light / Chapter 6.3 --- Short Temporal Gaussian Profile Incident Light / Chapter 6.4 --- Singly Resonant SBS / Chapter CHAPTER 7 --- CONCLUSION --- p.98 / APPENDIX A --- p.100 / APPENDIX B --- p.102 / APPENDIX C --- p.106 / APPENDIX D --- p.108 / REFERENCES --- p.120

Thesis (M.Sc.)--Memorial University of Newfoundland, 2005. / Restricted until October 2006. Bibliography: leaves 88-94.

The past decade has seen an increased interest in multiwavelength optical sources. Various methods and technologies exist for developing multiwavelength lasers with varying features and characteristics. A particular category that has gained much interest, are multiwavelength fiber lasers that combine nonlinear gain from stimulated Brillouin scattering with linear gain from erbium doped fibers. / This thesis demonstrates experimentally a Brillouin semiconductor multiwavelength fiber laser that utilizes semiconductor optical amplifiers as the linear gain medium. This novel technique allows for multiwavelength Brillouin fiber lasers to operate in any wavelength band for which SOAs are available. We begin by demonstrating a ring cavity configuration with a single wavelength output in the C/L bands. This configuration is enhanced for multiwavelength generation by the addition of a feedback path. The setup is then implemented in the O-band to demonste that the Brillouin fiber laser can be made to operate at any wavelength. Finally, several linear cavity configurations are explored and shown to improve the performance of the multiwavelength output in the O- and C/L- bands.

Thesis (Ph.D.)--McMaster University (Canada), 1995. / Source: Dissertation Abstracts International, Volume: 56-12, Section: B, page: 6844. Adviser: D. Walton.

Room temperature elastic properties of thin supported TiC films, deposited on silicon and silicon carbide substrates and of single Rh-based alloy crystals, Rh3Nb and Rh3Zr, are investigated by the Surface Brillouin Scattering (SBS) technique. Velocity dispersion curves of surface acoustic waves in TiC films of various thicknesses, deposited on each substrate (Si and SiC) were obtained from SBS spectra. Simulations of SBS spectra of TiC thin hard films on germanium, silicon, diamond and silicon substrates have been carried out over a range of film thickness from 5 nm to 700 nm. The simulations are based on the elastodynamic Green's functions method that predicts the surface displacement amplitudes of acoustic phonons. These simulations provide information essential for analysis of experimental data emerging from SBS experiments. There are striking differences in both the simulated and experimental SBS spectra depending on the respective elastic properties of the film and the substrate. In fast on slow systems (e.g. TiC on silicon), the Rayleigh mode is accompanied by both broad and sharp resonances; in slow on fast systems (e.g TiC on SiC), several orders of Sezawa modes are observed together with the Rayleigh mode. The velocity dispersion of the modes has been obtained experimentally for both situations, allowing the elastic constants of the films to be determined. Effects of two deposition conditions, RF power and substrate bias, on the properties of the films are also considered. Platinum metal group alloys are promising candidates for future ultra high temperatures gas turbines materials due to their excellent high-temperature properties. In the present work, room temperature elastic properties of single crystals of Rh3Nb and Rh3Zr are investigated. SBS spectra for a range of wave vector directions from the (001) surface have been acquired in order to determine the angular variation of the surface acoustic wave velocities and the longitudinal wave threshold within the Lamb shoulder. The elastic stiffnesses of the specimens were determined using two approaches; one approach involves a least-square fit of the experimental data to calculated results and the other is an analytical approach which involves the 2 c minimization of secular equations for the Rayleigh surface acoustic wave and the longitudinal wave threshold velocities in the [100] and [110] directions on the (001) surface of a cubic crystal. Results from the two methods were in good agreement.

No description available.

The sub-surface region of chemical vapour deposition (CVD) diamond was transformed by C+ ion implantation followed by isochronal annealing up to 1200 oC. Different implantation regimes and with different energies at different implantation temperatures would give different thicknesses were studied. This enabled a study in the evolution of the stiffness of the damaged layer as a function of annealing. The technique of choice for this study was the non-destructive Brillouin light scattering (BLS) utilizing two scattering geometries; indirectly scattered phonons (Kr¨uger-type geometry) for temperature anneals up to 600 oC, and the conventional surface ripple mechanism up to 1200 oC. It has been argued that surface acoustic waves (SAW) on a transparent medium are enhanced by applying a thin metallic reflective layer on the surface, this study has showed that opacity of the substrate is key. In fact, bulk modes with SAW-like characteristics emanating from indirect photon scattering off phonons after reflection at the smooth reflective back of the sample dominated down to transmission below 5% which was observed after annealing between 500-600 oC (low annealing temperatures). The other complementing techniques employed to understand the changing structure of the ion implanted diamond were Raman spectroscopy, electromagnetic transmission in the visible range, electron energy loss spectroscopy (EELS) and high-resolution transmission electron microscopy (HRTEM) in addition to theoretical techniques: transport of ions in matter (TRIM), finite element modelling (FEM) and elastodynamic Green’s functions. Although the electronic techniques showed a structurally changing material at the low annealing temperatures, the optical ones did not show significant changes in the ion-damaged material possibly due to lack of distinct interface between the pristine diamond and the ion irradiated region at these lower annealing temperatures.