Continuously pumped all-solid-state laser system with fiber phase conjugation

Stimulated Brillouin scattering (SBS) is a nonlinear optical process that generates backward scattered phase conjugate wave (Zel’dovich et al., 1972; Zel’dovich et al., 1985; Damzen et al., 2003; Brignon & Huignard, 2004). A device that generates the phase conjugate wave by the SBS process is called SBS phase conjugate mirror (PCM). An SBS-PCM can compensate wavefront distortion induced by a phase aberrator, such as a laser gain medium; hence, it is widely used in high-energy laser systems to obtain a high-quality beam. Efficient heat dissipation is a major issue in high-energy laser systems, particularly with regard to the high repetition rate. The combination of beams from small laser systems is a constructive approach to this issue. Of the various beam combined systems using SBS-PCMs, the crosstype beam combined system has many outstanding advantages, such as perfect isolation of leak beam, compensation of thermal birefringence, easy alignment and convenient maintenance (Kong et al., 1997, 2005a). Since the SBS wave generates from a thermal noise, it naturally has a random phase with respect to the incident beam. Therefore the phase controlling of the SBS wave is a key technology in the realization of a coherent beam combined system. For this reason, the self-phase control method was proposed and has been developed by Kong et al. (2005a, 2005b, 2005c), which can control the phase of the SBS wave with the simplest composition as well as ease of alignment, no limitations on the number of combined beams, and excellent phase conjugation. Furthermore, the active phase control with a piezoelectric translator (PZT) enables long-term phase stabilization (Kong et al., 2006, 2008). In addition to a random phase characteristic, the distortion that generally occurs in a pulse waveform of an SBS wave is another negative characteristic in terms of the beam combination. Kong et al. (2005d) has overcome this problem with the SBS waveform preservation technique, which is called the prepulse injection method. These works are expected to boost the development of laser systems in term of a high level of energy and

Phase conjugation by SBS (stimulated Brillouin scattering) is a powerful and simple tool to increase the beam quality of high power lasers up to the diffraction limit. Master oscillator and power amplifier systems with Nd:YAlO as active medium were realized with an average output power up to 210 watts at 1.08 micrometer in a near diffraction limited beam. Also Nd:YAG-oscillators with phase conjugating mirrors were realized with an average output power up to 17 watt and high beam quality. In the UV range, excimer oscillators with SBS mirrors deliver the same or better beam quality than conventional plane-plane resonators in 3 times shorter pulses. Excimer oscillator-amplifier arrangements have been realized with SBS mirrors. SBS mirrors for the visible and ultraviolet spectral range are well characterized. First experiments for an ordered passive fiber bundle with an SBS mirror show the possibilities and limitations to improve the beam quality of fiber bundle amplifies or even oscillators.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Summary form only. To investigate the ability of fiber phase conjugators to handle high average powers, and to realize all solid-state setups, pulsed laser systems were equipped with fiber phase conjugate mirrors (PCMs). The developed MOPA system is flash lamp pumped and consists of a master oscillator, an optical isolator, two amplifier heads in a serial arrangement and a 200 /spl mu/m multimode fiber as PCM.

Structured light with multiple degrees of freedom has inspired many advanced applications, and its nonlinear control plays an important role in the interactions between light and matter. Stimulated Brillouin scattering (SBS) based on light–sound coupling can be used to realize wavefront‐reversal nonlinear reflection of ordinary light; consequently, it is used to correct wavefront aberrations in high‐power laser systems. However, high‐fidelity wavefront reversal of structured light with orbital angular momentum and high‐reflectivity single‐end SBS of weak incident waves remain challenging. Here, the authors propose a cross‐pump focused SBS scheme that enables wavefront reversal with high fidelity, low threshold, and high reflectivity for arbitrary structured light . The authors demonstrate the capability of this approach to perform conformal and enhanced SBS reflections with a fidelity of >95% and reflectivity of >100%. Compared with the conventional focused SBS configuration, the SBS threshold is reduced by more than ten times, and wavefront reversal of weakly structured light is realized. This proof‐of‐principle study provides a high‐performance SBS platform with potential implications for high‐power structured lasers, high signal‐to‐noise‐ratio microscopy imaging, and the development of nonlinear optics with structured light.

Continuous wave (CW) stimulated Brillouin scattering (SBS) phase conjugation in step-index optical fibers was studied experimentally and modeled as a function of fiber length. A phase conjugate fidelity over 80% was measured from SBS in a 40 m fiber using a pinhole technique. Fidelity decreases with fiber length, and a fiber with a numerical aperture (NA) of 0.06 was found to generate good phase conjugation fidelity over longer lengths than a fiber with 0.13 NA. Modeling and experiment support previous work showing the maximum interaction length which yields a high fidelity phase conjugate beam is inversely proportional to the fiber NA(2), but find that fidelity remains high over much longer fiber lengths than previous models calculated. Conditions for SBS beam cleanup in step-index fibers are discussed.

The theoretical investigation and numerical simulation of phase conjugation (PC) at stimulated Brillouin scattering (SBS) with feedback is carried out. A case of long pulse PC is considered. At this condition both running and standing phase gratings which responsible for the positive feedback are taken to account. The threshold of PC wave generation and PC reflectivity are calculated. The numerical solution for temporal behavior of PC intensity is obtained.

Stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS) are two kinds of emblematic inelastic scattering processes resulting from the interaction of high-intensity laser with matter. Generally, competition between SBS and SRS is a common phenomenon in many substances. In liquid or high-pressure gas, if a single longitudinal mode laser is used as a pump source, both SBS and SRS can be excited, but the SBS will become very strong due to higher gain and optical phase conjugation. In comparison, the SRS gain is typically 2 orders of magnitude smaller than the SBS gain so that most of the pump laser energy is spent on the SBS and the SRS is greatly suppressed. To improve the output energy of SRS in liquid medium, a method of suppressing the SBS process by controlling temperature of medium is proposed. The SRS generation system using broadband pulse laser of 532 nm in wavelength as a pumping source is designed, the output energy of forward SRS (FSRS) and backward SBS (BSBS) in water with different temperatures are measured, and the physical mechanisms of the influences of water temperature, pumping linewidth and thermal defocusing on the output energy of SRS are analyzed. The experimental results indicate that by reducing the water temperature, the SBS process can be significantly suppressed, and the beam distortion caused by thermal defocusing effect can be reduced, thus effectively improving the output energy of SRS. Unlike the single longitudinal mode laser, when the pump source is handled in multiple longitudinal modes with a wide linewidth, the gain of FSRS is higher than that of the backward SRS (BSRS). Meanwhile, since the SBS gain coefficient is restricted by the linewidth of the pump laser, the FSRS process is dominant and both backward SBS and BSRS are significantly suppressed. It is necessary to state that none of the influence of backward SRS, self-focusing, optical breakdown and other non-linear effects on the output energy of SRS is considered in this paper, and only the effectiveness of reducing temperature to improve the energy output of forward SRS is verified from the perspective of temperature change. The results are of great significance for the multi-wavelength conversion of SRS in liquid medium.

The implementation of a stimulated Brillouin scattering (SBS) free, optical fibre phase conjugator by use of only 1 m length of fabricated bismuth oxide-based nonlinear fibre (Bi-NLF), has been experimentally demonstrated. A high OSNR phase-conjugated signal was readily achieved owing to the unique properties of the Bi-NLF such as an ultra-high χ(3) nonlinearity and a high SBS threshold although no SBS suppression scheme was employed. Using the phase conjugator, error-free transmission of the signal is readily achieved over a 150 km SMF link.

A flashlamp-pumped dye laser with a SBS phase-conjugate resonator

ABSTRACTStokes field demonstrated unusually narrow spectrum and non-Gaussian statistics for SBS in 300-rn single-mode opticalfiber with enhanced Rayleigh losses. We shown that SBS lasing takes place in the fiber. The effect is explained by dynamicdistributed feedback due to double Rayleigh scattering of the Stokes field. Results of numerical simulation of the cooperativeSBS-RS process in fiber are in good agreement with experimental results. 1. INTRODUCTION Stimulated Brillouin scattering (SBS) is the resonance interaction between pump wave backscattered optical Stokes wave,and hypersound wave induced in the medium. SBS is initiated by spontaneous scattering of the pump wave on occasionalhypersound waves caused by thermal noise. Being essentially nonlinear process, SBS in optical fibers demonstrates a complicateddynamic behavior'.The presence ofthe external feedback makes SBS dynamics even richer. Significant narrowing ofthe spectrumand decreasing ofthe SBS threshold are usually observed for SBS in fiber ring interferometers. Regularization ofthe Stokes fieldchaotic fluctuations and soliton mode generation are observed both in low fitness ring fiber resonators and in the long single-modeoptical fiber when small (—3%) parasitic reflections from the non-angled fiber ends creates low fitness Fabry-Perot interferometerin the fiber2._________________________________________________

Based on pump-probe technique (PPT), we observed stimulated Brillouin scattering (SBS) in a 100-m-long silica graded-index multimode optical fiber with the same core diameter as that of a perfluorinated graded-index polymer optical fiber (PFGI-POF) (= 50 μm). The SBS threshold was measured to be -50 mW, which was much lower than 5.08 W, the SBS threshold obtained for the same fiber without PPT. This result indicates that PPT is useful even under multimode conditions and that the difficulty in observing SBS in PFGI-POFs consists not in their physical problems but in their material problems (high propagation loss, etc.).

This work focuses on the study of stimulated Brillouin scattering (SBS) in optical fibers with a goal of studying its applicability for phase conjugation of radiation from CW lasers, and of using SBS to demonstrate high power fiber lasers by coherent combination of beams from several fiber amplifiers. Results revealed that both phase conjugation and beam cleanup behavior can take place via SBS in the 4.4 km MM fiber used, depending on the divergence of the input beam and the input power level.

Phase conjugation of excimer XeCl laser radiation by different kinds of stimulated scattering

Recently, high power narrow linewidth fiber lasers are interested in wavelength beam combining. In narrow linewidth fiber laser, Stimulated Brillouin Scattering is the main power limiting factor. A Stimulated Brillouin Scattering suppressing method by modulating frequency distribution was proposed and examined both experimentally and theoretically. The Stimulated Brillouin Scattering threshold power increased a lot by increasing the frequency number and spacing. Finally, the linewidth of 8 GHz, power of 1kW and central wavelength of 1064.14nm, are achieved respectively in fiber laser. We analyzed the above results: the increasing of frequency number, controlling of frequency spacing all reduce power spectrum density. With the cascaded phase modulation technology, the Stimulated Brillouin Scattering threshold is increased, while the output power of fiber laser is increased a lot.Recently, high power narrow linewidth fiber lasers are interested in wavelength beam combining. In narrow linewidth fiber laser, Stimulated Brillouin Scattering is the main power limiting factor. A Stimulated Brillouin Scattering suppressing method by modulating frequency distribution was proposed and examined both experimentally and theoretically. The Stimulated Brillouin Scattering threshold power increased a lot by increasing the frequency number and spacing. Finally, the linewidth of 8 GHz, power of 1kW and central wavelength of 1064.14nm, are achieved respectively in fiber laser. We analyzed the above results: the increasing of frequency number, controlling of frequency spacing all reduce power spectrum density. With the cascaded phase modulation technology, the Stimulated Brillouin Scattering threshold is increased, while the output power of fiber laser is increased a lot.

In order to measure the Brillouin linewidth of SBS medium, a method using mixture media in two-cell stimulated Brillouin scattering (SBS) system is proposed, which uses the medium to be measured as amplifier medium and the mixture media as generator medium. The profile of gain coefficient versus the difference of Brillouin frequency shift is fitted with Lorentzian curve. The width at half-maximum of this curve is the Brillouin linewidth. In the experiment, using Nd:YAG Q-switched laser system and CCl4/C6H6 mixture, we measured the Brillouin linewidth of SBS media tetrachloroethylene (C2Cl4), hexachlorobutadiene (C4Cl6), acetone (C3H6O) and n-hexane (C6H14). The results show that the measured values are close to those calculated or published by other authors.