Stimulated Brillouin Scattering Phase Conjugation Research Articles

Compensation of the thermally induced depolarization in a double-pass Nd:YAG rod amplifier with a stimulated Brillouin scattering phase conjugate mirror

Stimulated Brillouin scattering phase conjugate mirrors (SBS-PCMs) are extensively used to compensate the phase distortion of active media in a high-energy laser system with double-pass amplification. However, the depolarization loss from the thermally induced birefringence of the active medium by a photoelastic effect cannot be avoided despite the uses of phase conjugate mirrors. In this work, the depolarization loss in a double-pass Nd:YAG rod amplifier with a SBS-PCM has been studied with Jones matrix calculations. In addition, the depolarization ratios and the leak beam patterns are obtained experimentally and theoretically for four possible optical schemes. Both experiment and theoretical results show that depolarization is effectively compensated when a Faraday rotator is located after the amplifier.

Current Trends in Laser Fusion Driver and Beam Combination Laser System using Stimulated Brillouin Scattering Phase Conjugate Mirrors for a Fusion Driver

Laser facilities in the world have been developing flash-lamp-pumped ultrahigh-energy solid-state lasers for fusion research and high-repetition diode-pumped solid-state lasers to act as commercial fusion drivers. A commercial laser fusion driver requires a high-energy beam with a total energy of several megajoules per pulse in several nanoseconds with a ∼10-Hz repetition rate. However, current laser technologies have limitations in raising the beam energy when operating with a high repetition rate, which is necessary for a commercial fusion driver to function properly. The beam combination laser system, which that uses stimulated Brillouin scattering phase conjugate mirrors, is a promising candidate for a fusion driver because it can obtain both a high energy and a high repetition rate with separate amplifications. For the realization of the beam combination laser system, a self-phase control technique was proposed for the coherent beam combined output, and its principle was demonstrated experimentally.

A new circulating two-cell structure for stimulated Brillouin scattering phase conjugation mirrors with 1-J load and 10-Hz repetition rate

A new approach to realize high-energy and high-power stimulated Brillouin scattering phase conjugation mirrors (SBS-PCMs) is described. The reflectivity of SBS-PCM is investigated under a 10-Hz repetition rate and a high energy load. The relationship between reflectivity and input energy is examined experimentally with different PCM structures, focus lengths, and medium cell structures. A medium cell with a circulating structure is designed, and its advantage is demonstrated through an experimental comparison with traditional PCM structures. The 30-cm focus lens and 150-cm collimation lens are optimized when the input energy reaches 1010 mJ at 10-Hz repetition rate. Therefore, a reflectivity of 84.7% and a higher energy load using the circulating two-cell structure are achieved.

Wave-front dividing beam combined laser fusion driver using stimulated Brillouin scattering phase conjugation mirrors

The beam combination method using stimulated Brillouin scattering phase conjugation mirrors (SBS-PCMs) is a promising technique for a commercial laser fusion driver operated with a high repetition rate around 10 Hz. The phase control of the SBS wave is essential for realization of the coherent beam combined output in the beam combination. For this reason, we proposed the ‘self-phase control technique’ of the stimulated Brillouin scattering wave, and its principle has been demonstrated experimentally over the past several years. In this work, the experiments are performed for the phase stabilization of wave-front dividing two-beam and four-beam combined systems by reducing the beam pointing fluctuation of the laser source using a beam expansion.

A new measurement of stimulated Brillouin scattering phase conjugation fidelity for high pump energies

AbstractIn order to measure the phase conjugation-fidelity of stimulated Brillouin scattering with high pump energy more accurately and conveniently, a new measurement is proposed. According to the definition of the fidelity with optical field correlated integral, the method of recording the far-field by array camera is analyzed theoretically. By the method, an experiment for high energy stimulated Brillouin scattering is arranged, and the maximum energy of 3.42 J is achieved in a single-cell stimulated Brillouin scattering generator. For small pump pulse, the fidelity maintains a high value of more than 0.9. However, the reflectivity fluctuation is significant when the pump energy is larger than 1.5 J. As a result, the fidelity decreases gradually to 0.5 at the pump energy of 3.42 J. The reflectivity shows the same character of great fluctuation as the fidelity at high pump energy.

Phase stabilization of the amplitude dividing four-beam combined laser system using stimulated Brillouin scattering phase conjugate mirrors

AbstractThe beam combination method using stimulated Brillouin scattering phase conjugate mirrors (SBS-PCMs) is a promising technique for a high energy and high power laser output operating with a high repetition rate. The two-beam combined system was previously demonstrated with an amplitude dividing method. A four-beam combined laser system with amplitude dividing method is demonstrated in this work, and the phase stabilization experiment of this system is performed using the self phase control and the long-term stabilization technique. The phase differences between the SBS waves are stabilized with λ/30 and the fluctuation of the four-beam combined output energy is 6.16% during 2000 shots (200 s).

Piston error characteristics of the self-phase-controlled stimulated Brillouin scattering phase conjugate mirrors

It was reported by Kong et al. that the self-phase-controlled stimulated Brillouin scattering phase conjugate mirror (SBS-PCM) is useful for the beam combination laser amplifier system, which generally introduces a phase delay (piston error) between combined beams along separate optical paths. In this work, we have investigated the piston error characteristics of two schemes for self-phase-controlled SBS-PCMs, a collinear scheme and a triangular scheme. Experimental results show that the piston errors of the reflected beams are 2kδ and kδ for the former and the latter scheme, respectively, where k is the wave number and δ is the optical path difference (OPD) variation introduced into the pass.

Investigation of stimulated Brillouin scattering media perfluoro-compound and perfluoropolyether with a low absorption coefficient and high power-load ability

The correlations between stimulated Brillouin scattering (SBS) characteristics of perfluoro-compound (PFC) and perfluoropolyether (PFPE) and their chemical structure are analyzed in detail and a series of new PFC and PFPE are reported. In the Nd:YAG laser system, the absorption coefficient, optical breakdown threshold (OBT), SBS threshold, and Brillouin frequency shift of new media such as FC-87, FC-43, HT-55, and DET are measured. Parameters such as gain coefficient, Brillouin linewidth, and phonon lifetime are calculated. The results demonstrate their good SBS properties: the absorption coefficients are below 10(-3)cm(-1) and OBTs are above 100 GW/cm(2). These media also exhibit a series of unique physicochemical properties, i.e., high heat-resistance, high oxidation stability, good chemical inertness, and insulation properties. The discovery of new media not only diversifies SBS medium, but also improves the performance of the SBS system, thereby laying a good foundation for the application of a SBS phase conjugation mirror in a high-power laser system.

New SBS media——perfluorinated amines

The stimulated Brillouin scattering (SBS) media perfluorinated amines with good SBS characteristics have been discovered based on the dependence of SBS characteristics on the chemical structures. The SBS parameters of perfluorinated amines such as FC-131, FC-3283, FC-40, FC-43 and FC-70 have been measured or calculated. The results demonstrate that their absorption coefficients are below 10-3cm-1 and optical breakdown thresholds are above 100GW/cm2. The perfluorinated amines also exhibit a series of unique physicochemical properties, i.e., non-toxic property, low volatility, and high stability. The discovery not only diversifies the SBS media, but also improves the performance of SBS system, thereby laying a good foundation for the application of SBS phase conjugation mirror in high-power laser systems.

Laser fusion driver using stimulated Brillouin scattering phase conjugate mirrors by a self-density modulation

A new concept of laser fusion driver is proposed, which uses a beam combination technique with stimulated Brillouin scattering phase conjugate mirror (SBS-PCM). It is constructed systematically with a cross-type amplifier as a basic unit. In the first part of this paper, we introduce the cross-type laser amplifier using SBS-PCM, with several advantages by experimental results. These advantages are the ideal properties for practical laser fusion driver, such as the perfect isolation of leak beam, the compensation of thermally induced birefringence through the amplifiers, the easy maintenance and alignment insensitiveness, and the freely-scale-up energy. Next, some successful results for the phase control of SBS-PCM are presented, which is one of the main problems in the current beam combination laser using SBS-PCM. Particularly, a new technique for controlling the phase of SBS-PCM, “self-density modulation,” is introduced, which is the simplest ever among those reported. With the advantages of the cross-type amplifier using SBS-PCM and the novel method for controlling the phase of SBS-PCM, the proposed beam combination laser system is presented as the most promising one, which can contribute to the realization of high energy laser that can operate with high repetition rate over 10 Hz, even in the case of huge output energy over MJ.

Investigation on a high energy stimulated Brillouin scattering phase-conjugate mirror

A novel dual-cell Brillouin oscillator-amplifier phase conjugate mirror for high energy and high peak power operation in double-pass solid state laser amplifier is described. Correction of static aberration and dynamic aberration induced in single-pass amplifier was achieved in the second passage through the aberrating medium under the condition of using the stimulated Brillouin scattering phase conjugate mirror as reflector. Output energy of 13 J was obtained with input energy of 7.1 J. An energy reflectivity of 65% and a conjugation fidelity of 90% were achieved by the use of this dual-cell phase conjugate mirror. Finally, the performance of this kind of SBS reflector in a double-pass amplifier has been compared to that of a flat mirror. The results show that the SBS reflector is highly effective in correcting the spatial aberrations of laser radiation. Excellent near-and far-field conjugation fidelities were obtained even with high input energy.

Long term stabilization of the beam combination laser with a phase controlled stimulated Brillouin scattering phase conjugation mirrors for the laser fusion driver

Laser fusion requires very high energy/power output with high repetition rate over 10 Hz, which is very difficult with the current laser technologies. However, the recent research work on the phase controlling of the stimulated Brillouin scattering wave enables the realization of this kind of laser fusion driver. The recent progress of controlling the phase has been successfully demonstrated by the self-generated density modulation method proposed by one of the authors (Kong). Nevertheless, it showed a long-term fluctuation of the phase because of the long-term fluctuation of the density of the SBS medium due to the thermal fluctuation. This long-term thermal fluctuation is inevitable a fact in nature. The authors used a specially designed stabilizing system for the phase controlling system, which has the PZT control of the mirror for phase controlling SBS-PCM (the so-called feedback mirror). This system stabilizes the phase controlling system very well for more than 1 h. This technique will help the laser fusion driver to be realized sooner than expected. In addition, we propose a similar scheme to be applied to the ultra-fast pulse laser system, which must operate at high repetition rate for the laser fusion energy power plant.

Beam combined IFE driver using phase controlled stimulated Brillouin scattering phase conjugation mirrors

For inertial fusion energy (IFE) generation, the giant laser facilities have been constructed in the several countries. The recent laser driver technology can achieve the output energy more than 1 M-J. In addition, the recent works shows the fast ignition can reduce the required energy for the laser fusion. This seems to realize the laser fusion, but the repetition rate is not so high for obtaining the practical laser fusion energy. The beam combination laser is a promising candidate as the laser fusion driver because it can operate at the high repetition rate and it is easily scalable. In this paper, we introduce the beam combination technique using stimulated Brillouin scattering phase conjugate mirrors (SBS-PCMs), which was already proposed and shows the recent theoretical and experimental results about the phase controlling which is essentially required for the beam combination laser using SBS-PCMs.

Beam Combination using Stimulated Brillouin Scattering for the Ultimate High Power-Energy Laser System Operating at High Repetition Rate over 10 Hz for Laser Fusion Driver

After the laser was invented in 1960, a phase conjugation mirror has been respected to be the most fantastic one for the laser resonator composition because it can compensate any distortions of the laser beams occurred by the many inhomogenuities of the laser media and optical components. Among the many phase conjugation configurations, the stimulated Brillouin scattering phase conjugation mirror is the most simple one and many researchers have tried to utilize it to develop high power/energy laser systems. For realizing a high energy/power laser system the thermal problem is the most difficult to solve, and some researchers suggested a beam combination technique to reduce the thermal load of the big laser media to many small sized ones. To accomplish the beam combination using stimulated Brillouin scattering phase conjugation mirrors (SBS-PCMs), it is necessary to lock/control the phases of the SBS-PCMs. And some researchers have developed several ways for it, but they can lock the phases of a limited number of beams overlapped at the foci less than 5, or lock the phases by back-seeding technique but it loses the phase conjugation characteristics. For realization of the laser fusion driver, it is necessary to combine more than 10 or 100 beams. And the authors have developed recently a new phase controlling/locking technique which is isolated and independent totally from other beams and it can be applied to an unlimited number of beams in principle.

Great improvement of phase controlling of the entirely independent stimulated Brillouin scattering phase conjugate mirrors by balancing the pump energies

For developing a beam combination laser with the stimulated Brillouin scattering-phase conjugate mirrors (SBS-PCMs), the phase control of the backward SBS waves is essentially required. We proposed a new effective and practical technique in previous works, in which entirely independent SBS-PCMs are used, so that there is no limit of the number of the beams for the beam combination laser. In this letter, we show that in the proposed technique, the phase of the SBS wave significantly depends on the pump energy and it can be stabilized—although the independently separate SBS-PCMs are used—provided that the pump energies are balanced under the density modulation. In this experimental work, the standard deviation of the relative phase difference between the SBS waves has been reduced less than λ∕30 by the amplitude dividing method to provide the pump beams with the nearly same energies.

Beam combined laser fusion driver with high power and high repetition rate using stimulated Brillouin scattering phase conjugation mirrors and self-phase-locking

Volume 23, Number 1, Pages 55–59, 2005Below is the complete Reference citation for Neumayer et al. (2005).Neumayer, P., Bock, R., Borneis, S., Brambrink, E., Brand, H., Caird, J., Campbell, E.M., Gaul, E., Goette, S., Haefner, C., Hahn, T., Heuck, H.M., Hoffmann, D.H.H., Javorkova, D., Kluge, H.-J., Kuehl, Th., Kunzer, S., Merz, T., Onkels, E., Perry, M.D., Reemts, D., Roth, M., Samek, S., Schaumann, G., Schrader, F., Seelig, W., Tauschwitz, A., Thiel, R., Ursescu, D., Wiewior, P., Wittrock, U. & Zielbauer, B. (2005). Status of PHELIX laser and first experiments. Laser Part. Beams23, 87–93.

Beam combined laser fusion driver with high power and high repetition rate using stimulated Brillouin scattering phase conjugation mirrors and self-phase-locking

For achieving practically useful laser fusion energy generation, it is necessary to have a M-J laser system with a repetition rate over 10 Hz. We believe that a beam combination method using stimulated Brillouin scattering phase conjugate mirrors (SBS-PCM) is one of the most practical techniques for achieving the high repetition rate of the high power laser. In this paper, we present the recent results about the beam combination laser, such as SBS reflectivity depending on the mode structure, the cross type isolator, and the phase-locking technique. For the phase-locking technique, especially, the self-phase-locking is proposed and its result is discussed.

Highly repetitive high energy/power beam combination laser: IFE laser driver using independent phase control of stimulated Brillouin scattering phase conjugate mirrors and pre-pulse technique

A beam combination laser with stimulated Brillouin scattering-phase conjugate mirrors (SBS-PCMs), which is expected to produce a high output energy and power with a repetition rate over 10 Hz, is a candidate for a practically useful laser fusion driver in the future. In order to develop the beam combination laser with SBS-PCMs, it is necessary to control the phase of each SBS wave whose phases are known as inherently random. We have proposed a new phase control technique and demonstrated experimentally that the relative phase difference between two SBS waves can be controlled to a certain value and locked to it with an accuracy less than λ/4. Additionally we have proposed and demonstrated a new technique to preserve the pulse shape of the SBS wave. Based on these experimental results, we have proposed two schemes of the new schemes for the high repetition and high energy/power beam combination laser system (laser fusion driver) using the SBS-PCMs of amplitude division and wave-front division techniques, which can operate with repetition rate over 10 Hz, in this paper.

Phase control of a stimulated Brillouin scattering phase conjugate mirror by a self-generated density modulation

We report that the phase of a backward wave by stimulated Brillouin scattering (SBS) can be controlled by a self-generated density modulation without any backward Stokes seed beam, which is generated due to electrostriction induced by electromagnetic standing wave through the interferences between the main beam and the low intensity counter-propagating beam. The density modulation ignites the position of the Brillouin grating so that the phase of the backward SBS can be controlled. We obtained 96% success with the phase error less than a quarter wave under a proper scheme of the self-seeding methods. This phase control technique is so simple, scalable, and very efficient that it can be applied to many beam combination systems for a high power laser system with a high repetition rate over 10Hz.

Novel Design of Laser with SBS Phase Conjugation Mirror

The beam quality of a single-rod Nd: YAG laser with wavelength of 1.06 μm was improved almost up to the diffraction limit by using a phase-conjugating mirror (PCM) based on stimulated Brillouin scattering (SBS) with acetone as the SBS medium. The new start cavity, which is the concave-convex cavity operating near the limit of stability in the g diagram, and the phase conjugation cavity of the SBS oscillator were designed. The thermal lens of the material with focal lengths of less than 140 m at pump powers of 60 J was compensated by the PCM. The laser is Q-switched by the nonlinear reflectivity of the PCM and the system works with an average repetition rate of about 5 kHz and single Q-switch pulse showed a width of 10 ns. It is demonstrated that if the start cavity is fit for SBS and the SBS phase conjugation mirror can be optimized, the beam quality of solid laser can be surely enhanced because of this technology of nonlinear optics.