Stimulated Brillouin Scattering Phase Conjugate Mirrors Research Articles

High temporal waveform fidelity stimulated Brillouin scattering phase conjugate mirror using Novec-7500.

A high temporal waveform fidelity stimulated Brillouin scattering phase conjugate mirror (SBS-PCM) with high energy efficiency, based on a novel medium, Novec-7500, is proposed and practically achieved in this study. A theoretical analysis reveals that the temporal-domain waveform distortion is caused by the inherent pulse duration compression effect of the SBS, and this undesirable phenomenon can be significantly suppressed by decreasing the compression coefficient (CC afterwards), which is defined as the gain coefficient divided by the phonon lifetime, which coefficient and is identified as the key parameter for high waveform-fidelity in SBS-PCM. The feasibility of this approach was demonstrated experimentally, in which a reflected pulse with waveform symmetry equals to the pump and an average pulse duration of 0.974 τp (τp is the duration of pump) with an energy efficiency of over 90% was achieved using Novec-7500.

Application progress of the stimulated Brillouin scattering phase conjugate mirror in high power nanosecond lasers

Stimulated Brillouin Scattering (SBS) is a third-order nonlinear optical effect, the reflected beam of which has the property of phase conjugation. The reflected beam is time inversed on amplitude, phase and polarization with the incident beam and maintains the same wavefront as the incident light. In the Master Oscillator Power Amplifier (MOPA) nanosecond laser system, the thermal effect in the laser amplifiers and a large number of optical elements in the optical path cause serious wavefront distortion of the transmitted beam, which not only deteriorates the beam quality, but also limits the possibility of further power improvement. Stimulated Brillouin Scattering Phase Conjugate Mirror (SBS-PCM) is utilized widely in this kind of laser system for the fact that using SBS-PCM by making the beam transmit along a round trip in amplifiers which bring in serious wavefront distortion compensates the distortion in real time, therefore is capable of optimizing the beam quality and improving the output power, so as to promote the development of nanosecond laser system in the direction of both high power and high beam quality. In this paper, the basic principle and phase conjugation characteristics of SBS-PCM were briefly introduced theoretically. Then the characteristics and application scope of different SBS-PCM media were compared. The research progress by domestic and foreign institutions on SBS-PCM and the typical application and development process of SBS-PCM in high power nanosecond lasers were summarized. Finally, the development trend of SBS-PCM was prospected.

High beam quality of nanosecond Nd:YAG slab laser system with SBS-PCM

All-solid-state nanosecond laser has a wide application prospect, but it remains an outstanding challenge to achieve high-power output with excellent beam quality. An optimized slab-amplifier-based laser system was demonstrated with 600 mJ output energy, 9.3 ns pulse duration and 200 Hz repetition rate. Most importantly, the beam quality M2 reached to approximately 2, which can be attributed to the improvement of spatial profile of near/far-field by the stimulated Brillouin scattering phase conjugation mirror (SBS-PCM). The comprehensive performance shows that the slab laser adopting SBS-PCM is a promising technical solution for high power laser system.

1.5 J high-beam-quality Nd:LuAG ceramic active mirror laser amplifier

A 1.5 J Nd:LuAG ceramic active mirror laser amplifier with a high beam quality is demonstrated in which a 0.8% (atomic fraction) Nd-doped Nd:LuAG ceramic disk with a diameter of 64 mm and a thickness of 5.5 mm is used as a laser gain medium. A maximum single-pass small-signal gain of 2.59 is measured when the pump energy is 11.5 J, with an injected seed energy of 0.4 J; a maximum output energy of 1.5 J is obtained at the repetition rate of 10 Hz. A far-field beam spot 1.25 times the diffraction limit (DL) is achieved by using a stimulated Brillouin scattering phase conjugation mirror (SBS-PCM) for wavefront correction.

High-repetition-rate, high-pulse-energy, and high-beam-quality laser system using an ultraclean closed-type SBS-PCM.

We present a high-repetition-rate, high-pulse-energy, high-beam-quality, and high-average-power laser system using an ultraclean closed-type stimulated-Brillouin-scattering phase-conjugate mirror (SBS-PCM). By controlling microparticles of SBS-PCM down to 40 nm, thermal load capacity of such closed-type SBS-PCM was greatly improved, which presented the best reported cleanliness. The closed-type SBS-PCM, lacking scanning wedge plates, achieved reflectivity as high as 92% and showed no optical breakdown phenomena or obvious thermal effects at a 500 Hz pulse-repetition frequency (PRF). Operation at 550 W output power, approximately 1.1 J pulse energy, and beam quality M2 of approximately 2 represents, to our knowledge, the best reported performance. Thermal phase distortion was compensated, and the maximum-output-power pulse-width compression improved from 30 ns to approximately 10 ns.

Experimental study on SBS-PCM at 200 Hz repetition rate pumped with joule-level energy

In this paper, an experiment is designed to research the properties of the stimulated Brillouin scattering phase conjugation mirror (SBS-PCM) working under joule-level pump energy and 200 Hz repetition rate. The nonlinear medium FC-770 is chosen as the SBS medium working in high-power condition. Due to the excellent preparation process and ultra-filtration technology for SBS-PCM, there is no optical breakdown phenomenon under the reflectivity maintained at 98% under 200 Hz and pump energy from 500 mJ to 1100 mJ. Under 800 mJ pump energy, the diffraction fringes of the near-field pattern are reduced and the beam quality of the laser beam has been improved to 1.42 times diffraction limited after the double-pass amplification from the single-pass 2.01 times diffraction limited. The incident and reflected pulse width are becoming wider with pump energy increasing. When the pump energy reaches a certain extent, the reflected pulse width will become nearly approximate to the incident pulse width. When the pump energy is 800 mJ, the pump pulse width is 40.3 ns and the output pulse width is 38.8 ns.

Coherent beam combination using self-phase locked stimulated Brillouin scattering phase conjugate mirrors with a rotating wedge for high power laser generation.

The self-phase locking of a stimulated Brillouin scattering-phase conjugate mirror (SBS-PCM) allows a simple and scalable coherent beam combination of existing lasers. We propose a simple optical system composed of a rotating wedge and a concave mirror to overcome the power limit of the SBS-PCM. Its phase locking ability and the usefulness on the beam-combination laser are demonstrated experimentally. A four-beam combination is demonstrated using this SBS-PCM scheme. The relative phases between the beams were measured to be less than λ/24.7.

Spatial resolution-preserving retroreflection for gas-phase laser scattering measurements in turbulent flames using a phase-conjugate mirror.

This Letter reports on the demonstration of a stimulated Brillouin-scattering phase conjugate mirror (SBS-PCM) for multipass laser-based scattering measurements in turbulent flames. Retroreflective measurements using the SBS-PCM show substantial improvements in spatial-resolution preservation as compared to measurements using a conventional mirror as a multipass reflector. The results using the SBS-PCM indicate an insensitivity to large index-of-refraction gradients and preservation of the original spatial resolution as defined by the laser beam under reacting flow conditions. This approach offers the possibility of increasing signal-to-noise ratios within low-signal gas-phase measurements such as Rayleigh and Raman scattering.

高平均功率光纤受激布里渊散射相位共轭镜的研究与探讨

高平均功率光纤受激布里渊散射相位共轭镜的研究与探讨

Research on the compression properties of FC-3283 and FC-770 for generating pulse of hundreds picoseconds

AbstractThis paper gives out two kinds of novel well-behaved stimulated Brillouin scattering (SBS) mediums, FC-3283 and FC-770. Numerical calculation and experimental measurements show these two mediums both having lower absorption, higher optical loads and short phonon lifetime, which making them good candidate mediums for high-energy high-power SBS. Using them as the mediums in the compacted two-cell SBS phase-conjugation mirror, it is easily to generate ultrashort phased-conjugated Stokes pulses just with hundreds picoseconds. When the incident light energy is beyond 200 mJ, the pulse width of 8 ns can be compressed to 200 ps or less in both mediums. Especially, the FC-770 is very suitable to be chosen for generating the SBS picosecond pulses with the narrowest compression pulse width of 109 ps and the highest energy reflectivity of 80%.

0.4 J/10 ns/10 kHz‐4 kW coherent beam combined laser using stimulated Brillouin scattering phase conjugation mirrors for industrial applications

AbstractA laser system that can produce 0.4 J/10 ns/10 kHz‐4 kW using a coherent beam combination with stimulated Brillouin scattering phase conjugate mirrors (SBS‐PCMs) is proposed. The 4 kW coherent beam combination laser system consists of a front‐end system, a pre‐amplifier module, a coherent beam divider/combiner, and 4 main amplifier modules. The front‐end system produces 1064 nm @ 10 kHz laser pulses, and it is amplified by the pre‐amplifier. After the pre‐amplifier module, the laser beam is divided into 4 sub‐beams. Each sub‐beam is amplified by the main amplifier module in a double‐pass configuration and reflected by SBS‐PCMs. Sub‐beams are combined by a coherent beam combiner, and the output of the total system is designed to be 4 kW. With this 4 kW laser module, high‐speed 2D holographic laser processing will be utilized. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Characteristics of SBS hundreds picosecond pulse compression and influence of energy on pulse stability in FC-770

A prominent application of stimulated Brillouin scattering (SBS) is pulse sequence compression for obtaining high power and high intensity optical pulse. The characteristics and the stability of the compressed Stokes pulse were investigated using compact two-cell SBS phase-conjugation mirror. FC-770, having low absorption and high breakdown threshold at the wavelength of 1064nm, was used as the SBS medium. Both the Stokes pulse width and the reflectivity were measured as a function of incident pump energy. In our work, a 8ns laser pulse of 1064nm generated by Q-switched Nd: YAG was optimally compressed to 116ps for pump energies of 310mJ, while the energy reflectivity is above 85%. The shortest pulses width obtained exhibit 99ps duration. The stability of the temporal pulse widths after compression was investigated statistically. For non-optimal pump energies pulse widths become larger and the stability is found to decrease.

Four-Beam Coherent Combination by Stimulated Brillouin Scattering with Wavefront Division

Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea(Received 1 February 2010, in final form 10 July 2010)Using stimulated Brillouin scattering phase conjugate mirrors (SBS-PCMs), we conducted a co-herent beam combination of wavefront-divided beams. “Self-phase-controlled” SBS-PCMs wereused to lock and control the phases of the SBS wave. Using an interferometer, we monitored therelative phase differences of the four spatially divided beams in real time. With long-term phasestabilization, the phase differences between the reference beam and the other three beams were wellstabilized at standard deviations of λ/36.3, λ/35.8, and λ/43.4 for a duration of 2500 shots (250 s).

Investigation on high power phase compensation of strong aberrations via stimulated Brillouin scattering

The strong wave-front aberrations compensated by stimulated Brillouin scattering phase conjugate mirror (SBS-PCM) in a high power laser were investigated experimentally. The wave-front fluctuation of the 10 Hz 500 mJ Nd:YAG laser is 0.5λ. Transmitting through a random phase plate (RPP), it increases to 8.6λ. While using SBS-PCM in place of a high reflection mirror, the distortion induced by the RPP is compensated, and the wave-front fluctuation becomes 0.9λ. At the same time, obvious breakdown phenomena in the SBS cell were observed, and the reflectivity is unstable. A rotating wedge plate is introduced into the phase conjugating mirror to make the focus of the SBS cell rotate and optical breakdown is avoided effectively. The reflectivity becomes stable around about 70% and the instability is changed from ±4.1% to ±0.9%. Besides, the compensated wave-front fluctuation is only 0.6λ, which is near to the original wave-front distribution. The results show that the reflectivity of the SBS-PCM is very high and stable when there are no other nonlinear effects such as optical breakdown. Thus the compensating effects for strong wave-front errors are perfect.

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.

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).

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.

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.