The main goal of this paper is the study of the stimulated Brillouin scattering (SBS) in multimode fibers, at 1550 nm wavelength, cw operation, in order to build high power IR fiber lasers. Two theoretical models are considered, the usual plane wave model and a modal model, developed in this paper. The theoretical results for SBS threshold and SBS reflectivity are compared with the experimentally determined values. Good agreement was obtained when using the mode structure analysis.
In this paper, we demonstrate a (3D) analytical solution of stimulated Brillouin scattering (SBS) for high reflectivity and fidelity phase conjugation mirrors (PCM). The results are checked with experimental ones, which were obtained with CS2 and optical fibers as nonlinear materials and high PCM reflectivities are found out. Furthermore, analytical SBS reflectivity for pumping with Gauss-Laguerre modes is demonstrated and shown to suppress high modes, when using SBS mirrors. These findings are used in some all solid-state laser (SSL) systems with SBS-PCM in order to obtain near Gaussian beams, depolarization compensation and high brightness.
Reflectivity and fidelity of phase conjugation by stimulated Brillouin scattering (SBS) is studied in CS2. Experimental results are presented for TEM00 and TEM01 mode pumping, at 1.06 μm. SBS reflectivity has been analytically calculated and compared with experimental data. Good healing of phase distortions was demonstrated.
Phase conjugate mirrors based on stimulated Brillouin scattering (SBS) in multimode undoped quartz fibers can be operated with high reflectivity. The reflectivity and threshold of the SBS process and the damage threshold of the fiber entrance surface were measured for fibers with core diameter of 25, 50, 100, 200 micrometers . With calibration of the measurement system such fibers can operate with more than 80% reflectivity and the damage threshold lies above 0.9 GW/cm2. The SBS threshold is between 0.3 and 26 kW for all fibers investigated.
A three-dimensional wave model for the stimulated Brillouin scattering (SBS) is built and analytically treated, in case of slowly varying envelope approximation and stationary regime. More complete analytical expressions for pump and Stokes wave intensities and for SBS reflectivity are found. A good agreement between theoretical and experimental data for reflectivities is shown for Gaussian transverse profile of the pump beam.
All-solid-state laser sources are required for numerous applications in industry and science. Scaling of average output power while preserving a diffraction limited beam quality results in high brightness operation. However, conventional laser systems suffer from thermally induced phase distortions in the active medium, which considerably reduce their beam quality. Advanced pumping geometry, diode pumping, as well as active media with high quantum efficiency can reduce the thermal load. But the remaining phase distortions result in a reduction of beam quality. Optical phase conjugate mirrors are suitable to compensate for phase distortions in master oscillator power amplifier systems (MOPA). Stimulated Brillouin scattering in conventional, commercially available silica fibers facilitates reliable and stable phase conjugation. These all-solid state devices reveal an energy reflectivity of almost 90% and require low financial efforts. Moreover, the SBS threshold is determined by the appropriate fiber core diameter. Therefore fiber phase conjugators can be applied in continuously pumped, repetitively q-switched laser systems which usually exhibit smaller peak power in comparison with pulsed pumped systems. A four-pass amplifier arrangement with birefringence compensation was developed. Nearly diffraction limited output with 32 W average power has been achieved at 10 kHz repetition rate. Power scaling up to 100 W seems to be possible.
The beam quality of solid-state lasers with high average power can be greatly improved using phase conjugators based on stimulated Brillouin scattering (SBS). The common phase conjugators used until now are liquid or gas cells.Using SBS in glass fibers as phase conjugators the field of applications can be expended. The long interaction length and small cross-sections of the fibers result in an appreciable reduction of SBS threshold and avoid optical breakdown which could happen in liquids and gases at high input energies. Other advantages of glass fiber phase conjugators are harmlessness and easy handling. We have experimentally investigate a phase conjugator base don SBS obtained in an undoped quartz fiber with core diameter of 200 micrometers . The SBS threshold reflectivity and phase conjugation capability were measured with 18 ns pulses at 1.06 micrometers wavelength with different input energies.
We report Q-switching of a Nd:YAG laser with a phase-conjugating mirror based on external stimulated Brillouin scattering in carbon disulfide using a linear resonator. Q-switching is provided by a nonlinear LiF:F2- crystal before the stimulated Brillouin scattering takes place. Employing proper mode selectors pulses with 6 mJ minimum energy and duration of 20 ns were generated, the beam divergence being 1.5 the diffraction limit. A new theoretical model of the Q-switching regime has been proposed and good agreement between experimental and theoretical data has been obtained.
We report Q-switching of a Nd:YAG laser with a phase-conjugation mirror based on external external stimulated Brillouin scattering in CS2, using a ring resonator. Pulses with 5 mJ minimum energy and duration of 15 ns, at 2 Hz repetition rate, in the TEM00 mode were generated. A numerical simulation of the Q-switching regime has been made and good agreement between theoretical and experimental data has been obtained.
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