Stimulated Brillouin Scattering Pulse Compression Research Articles

Angular bandwidth for the non-focusing stimulated Brillouin scattering pulse compression

Laser pulse duration compression by stimulated Brillouin scattering (SBS) with a non-focusing scheme is a suitable candidate for high energy sub-nanosecond pulse generation owing to its high load capability and simple structure. The angular deviation of the feedback seed from the pump light path has a serious impact on the non-focusing SBS pulse compression. In this paper, we study the influence of this effect both numerically and experimentally. Firstly the pulse compression characteristics of 20th-order super-Gaussian-shaped pulses with 5 ns duration are analyzed theoretically. Then an experiment was carried out with a single-frequency high power Nd:glass laser system at the frequency-doubled wavelength of 527 nm which delivers 5 ns super-Gaussian-shaped pulses with single pulse energy over 10 J. Heavy fluorocarbon liquid FC-40 was used as the active SBS medium. The compressed pulse duration of sub-400 ps with an energy efficiency of ∼ 50 % is obtained when the laser is normally incident on the rear cell window. ± 4° deviation between the feedback Stokes light and pump laser halves the energy efficiency and doubles the compressed pulse duration. The experimental results agree well with the numerical calculations. The results of this paper will provide a basis for the design of self-pumped SBS pulse compressor and pave a way for higher energy sub-nanosecond pulse generation in the future.

A 115 ps, 100 Hz high-beam-quality laser based on transient stimulated Brillouin scattering pulse compression

Abstract This work demonstrates the generation of short pulse duration and high-beam-quality laser pulses using transient stimulated Brillouin scattering at a high repetition rate. Thermal effects and optical breakdown are identified as the main factors that restrict energy reflectivity and beam quality under high repetition rates and transient situations. Through experimental analysis, the interaction length and focal point size are determined to be the key parameters in reducing the thermal effect by reducing the absorption of the laser pulse by the medium. The obtained results show that pulses with a duration of 175 ps and beam quality M2 of around 1.2 can be achieved with a maximum energy reflectivity of over 40% under an interaction length of 50 mm. Furthermore, at an interaction length of 90 mm, a pulse output with a minimum duration of 115 ps (0.5τQ) is achieved.

Thermal suppression of high-repetition rate SBS pulse compression in liquid media.

Thermal problems of high-repetition-rate stimulated Brillouin scattering (SBS) pulse compression in liquid media are theoretically and experimentally analyzed in detail. A wedge lens with less coma-aberration was designed using the ray tracing method and the thermally induced beam-pattern distortion was compensated by inhibiting thermal convection. The heat transfer form and fluid state were quantitatively analyzed for different SBS liquid media. For a 74-W pump power, 3-kHz pulse-compressed phase-conjugation mirror with an energy efficiency of 36.2% is achieved. A potential optimization method of continuously adjusting SBS output characteristics using a mixed medium is proposed and theoretically demonstrated, to improve energy efficiency.

Output characteristics of high-power stimulated Brillouin scattering pulse compression enhanced by thermal effects based on HT270

Abstract Thermal effects are typically considered as obstacles to high-repetition-rate stimulated Brillouin scattering (SBS) pulse compression. In this paper, a novel method is proposed for improving the SBS output characteristics by exploiting thermal effects on the liquid medium. Using HT270, the SBS output parameters with the medium purification and rotating off-centered lens methods are studied at different repetition rates. The results indicate that these two methods can alleviate thermal effects and improve the energy efficiency, but the rotating method reduces the energy stability because of the aggravated optical breakdown at the kilohertz-level repetition rate. For a 35-mJ pump energy, the energy efficiency at 2 kHz without the rotating method is 30% higher than that at 100 Hz and 70% higher than that at 500 Hz. The enhancement of the SBS output characteristics by thermal effects is demonstrated theoretically and experimentally, and 2-kHz high-power SBS pulse compression is achieved with HT270.

Developments of Picosecond Lasers Based on Stimulated Brillouin Scattering Pulse Compression

Pulse compression based on stimulated Brillouin scattering (SBS) is a nonlinear optical approach that efficiently converts high-energy nanosecond pulses into the picosecond. Since the first observation of SBS pulse compression, different compression structures for different input and output parameters were developed to optimize the characteristics of pulse compression in the past decades. Here, a comprehensive review of the development status of SBS pulse compression schemes is provided, meanwhile, methods and trends to the optimization of SBS pulse compression are proposed.

Research progress of stimulated Brillouin scattering pulse compression technique

Stimulated Brillouin scattering (SBS) as a third-order optical effect is widely used in laser beam combination, distributed fiber sensing, Brillouin lasers and other fields. In recent years, SBS pulse compression has also received special attention. Based on the energy transfer characteristics of the Brillouin amplification process, SBS pulse compression technology can compress nanosecond pulses to sub-nanosecond levels, and the peak power can be increased by 1-2 orders of magnitude. This paper systematically introduces the basic theory of SBS pulse compression, comprehensively discusses the influence of SBS compressor structure, gain medium, pump pulse and other factors on pulse compression characteristics, and looks forward to the development trends of SBS pulse compression. It provides a useful reference for the future study of SBS characteristics and a feasible scheme for the acquisition of high repetition frequency and high energy laser.

Sub-nanosecond stimulated Brillouin scattering pulse compression using HT270 for kHz repetition rate operation.

With mitigation of thermal effects in a generator cell based on a rotating off-centered lens, the effects of thermal blooming, self-defocusing, and thermal convection in the amplifier cell have experimentally proven to be the main factors limiting high-repetition-rate stimulated Brillouin scattering (SBS) pulse compression. To alleviate these effects, Galden HT270, which has a large viscosity coefficient, is used and compared experimentally. The operating repetition rate using HT270 was improved from 200 Hz to 1,000 Hz, comparable to the values in the literature. With a pump energy of 50 mJ at 1,000 Hz, the pump pulse was compressed down to 820 ps using HT270 with an energy efficiency of 52.2%. If the injection energy is further increased, the SBS energy efficiency can be increased beyond this value.

High-Efficiency Optical Parametric Oscillator Based on Stimulated Brillouin Scattering Pulse Shaping

We present an optical parametric oscillator (OPO) that uses a pump pulse shape tailored by stimulated Brillouin scattering. The theoretical analysis is carried out for comparison between Gaussian pump and the step function pulse pump. The steep leading edge of the pulse helps minimize the buildup time of the OPO when applied to step function pulse. The study then focuses on obtaining step function pulse through stimulated Brillouin scattering pulse compression. With this control of the pump pulse's temporal shape, the experimental OPO energy conversion efficiency is 34.3%. Compared with an OPO pumped by a Gaussian-shaped pulse, the oscillation threshold is reduced and the energy conversion efficiency is improved by around 10%.

Pulse-shape dependence of stimulated Brillouin scattering pulse compression to sub-phonon lifetime.

A new approach to sub-phonon lifetime pulse compression by stimulated Brillouin scattering (SBS) is presented. Triangular and step pulse pumps are both used as a pump source in a single-cell SBS compression setup. Compared with a Gaussian pump (shortest compressed pulse is the phonon lifetime with the highest energy conversion, approximately 60% under the same conditions), the compression ratio is significantly improved in the case of triangular and step pulse pumps, and there is some improvement in the energy conversion when a step pulse pump is used. A pulse as short as a quarter of a phonon lifetime is produced by a triangular pulse pump, with an energy conversion above 30%. The pump pulse shape is identified as the key parameter in achieving sub-phonon lifetime pulse compression. By using a step pulse shape, a 4.5 ns pump pulses with a 60mJ at 1064-nm are compressed down to 292 ps (below semi-phonon-lifetime) in 3M Fluorinert Electronic Liquid FC-770 with an energy conversion above 65%. This work presents a route to reliable generation of sub-semi-phonon-lifetime pulses by SBS compression.

Fluctuation initiation of Stokes signal and its effect on stimulated Brillouin scattering pulse compression.

In this paper, a theoretical model is developed to demonstrate that fluctuations in the Stokes signal and occurrence position contribute to the final compression ratio in stimulated Brillouin scattering (SBS). This theoretical analysis can be applied to the investigation of the temporal characteristics of SBS pulse compression. This model agrees well with the experimental results in a two-stage SBS compressor.

SRS characteristics and its influence on SBS pulse compression in a fluorocarbon liquid

AbstractIn this paper, the occurrence of the stimulated Raman scattering (SRS) and its effects on stimulated Brillouin scattering (SBS) pulse compression in FC-40 are investigated. As the experimental medium, the characteristics of FC-40 are suitable for pulse compression. Firstly, the frequency shifts and the threshold of SRS in FC-40 are studied with a mode-locked laser system as pump source, without taking the SBS effect into account. On the basis of the experimental results, the competition between SRS and SBS as well as its effect on pulse compression is investigated. Results show that SRS gets higher gain and grows rapidly with the increase of the laser intensity by pump effect, which will result in decreasing of SBS energy reflection.

Tail modulation suppression in the process of high-energy stimulated Brillouin scattering pulse compression

AbstractWe report that the tail modulation of Stokes pulses in the high-energy stimulated Brillouin scattering pulse compression can be suppressed by controlling effective pulse width of the pump. It is shown through numerical simulations and validated experimentally that the effective pulse width is an appropriate parameter, which determines the generation of tail modulation. The effective pulse width broaden as the increase of energy. This mechanism leads to the amplification of Stokes tail edge and it is the cause of tail modulation.

Spatio-temporal characterization of pulses obtained from a high-energy sub-nanosecond laser system.

Spatio-temporal profiles of laser pulses, obtained from each stage of a high-energy sub-nanosecond laser system, are investigated. The laser system is composed of a Q-switched Nd:YAG unstable oscillator, a chain of Nd:YAG amplifiers, a second-harmonic generator, and a high-energy pulse compressor based on stimulated Brillouin scattering (SBS). A curved energy front, i.e., the pulses emerging away from the beam center being gradually delayed from the center pulse, is shown to originate from the unstable oscillator. Our comparative study shows that injection seeding will enlarge the energy front curvature, via reduction of the effective gain. After the laser amplifiers, the energy front curvature is more than doubled due to the gain saturation effect. The latter also modifies the spatial pulse width distribution. While there is a negligible pulse duration spread across the oscillator beam, the amplified pulses are found to have gradually reduced pulse duration away from the beam center. More interestingly, after the SBS pulse compression, not only the pulse width but also the delay is compressed down. This is, to the best of our knowledge, the first study of the spatio-temporal profile of the SBS compressed pulse. To compare with the experiments, two numerical models are developed to simulate the evolution of spatio-temporal profiles within the Nd:YAG laser system and during the SBS pulse compression, respectively. The first model is demonstrated to reproduce the experimental results very well, while the second model predicts part of the features of the SBS compressed pulse. The limitation on the latter is discussed.

High Compact, High Quality Single Longitudinal Mode Hundred Picoseconds Laser Based on Stimulated Brillouin Scattering Pulse Compression

A high beam quality hundred picoseconds single-longitudinal-mode (SLM) laser is demonstrated based on stimulated Brillouin scattering (SBS) pulse compression and aberration compensation. Flash-lamp-pumped Q-switched Nd3+:Y3Al5O12 (Nd:YAG) SLM laser with Cr4+:Y3Al5O12 (Cr4+:YAG) as a saturable absorber is used as the seed source. By combining master-oscillator-power-amplifier (MOPA), a compact single-cell with FC-770 as working medium is generated as pulse compressor. The 7.8 ns SLM laser is temporally compressed to about 450 ps, and 200 mJ energy is obtained at 1064 nm without optical damage. The energy stability is better than 3% with beam quality factor M2 less than 1.8, which makes this laser system an attractive source for scientific and industrial applications.

Generation of high-energy 284 ps laser pulse without tail modulation by stimulated Brillouin scattering

We obtain the output of a 284 ps pulse duration without tail modulation based on stimulated Brillouin scattering (SBS) pulse compression pumped by an 8 ns-pulse-duration, 1064 nm-wavelength Q-switched Nd:YAG laser. To suppress the tail modulation in SBS pulse compression, proper attenuators, which can control the pump energy within a rational range, are added in a generator-amplifier setup. The experimental result shows that the effective energy conversion efficiency triples when the pump energy reaches 700 mJ to 51%, compared with the conventional generator-amplifier setup.

Characteristics of perfluorinated amine media for stimulated Brillouin scattering in hundreds of picoseconds pulse compression at 532 nm

The characteristics of stimulated Brillouin scattering (SBS) in perfluorinated amine media and the experimental structure used in hundreds of picoseconds pulse compression at 532 nm are demonstrated. A two-stage SBS pulse compression structure is adopted for this work. The compact double-cell SBS compression structure and the scattering media FC-70 are chosen to compress the incident light from 9.5 to about 1 ns in the first stage. Then, the light is used as the pumping source for the second pulse compression. In the second stage, using a single-cell SBS structure in a pulse compression system, perfluorinated amine media with different phonon lifetimes, such as FC-3283, FC-40, FC-43, and FC-70, are chosen to run the comparative experimental study. The narrowest compressed pulse times obtained are 294, 274, 277, and 194 ps; they respectively correspond to the above listed media. The average width of the compressed pulse width is 320 ps for FC-3283, with a fluctuation range of 87 ps. For FC-40, the average pulse width is 320 ps, with a fluctuation range of 72 ps. And for FC-43, the average pulse width is 335 ps, with a fluctuation range of 88 ps. However, the average pulse width is only 280 ps for FC-70, with a fluctuation range of 57 ps. The highest energy reflectivity is more than 80% for all of the media. The experimental results show that a two-stage SBS pulse compression system has lower pump energy requirements, thus making it easier to achieve a compressed pulse waveform. The results also show that the shorter the phonon lifetime of the medium, the narrower the obtained compressed pulse width.

High stability, single frequency, 300 mJ, 130 ps laser pulse generation based on stimulated Brillouin scattering pulse compression

AbstractWe obtained the output of single frequency laser pulses with an average pulse-width of 136 ps and the minimum of 123 ps based on stimulated Brillouin scattering pulse compression pumped by an 8 ns-pulse-width, 1064 nm-wavelength Q-switched Nd:YAG laser. The pulse-width stability of the output is about 4.1% while that of the pump pulses is about 1.1%, the highest energy conversion efficiency is about 85%, and the single pulse energy is above 300 mJ.

An unusual pulse compression of stimulated Brillouin scattering in water

Pulse compression is an important property of stimulated Brillouin scattering (SBS), and the SBS pulse duration becomes smaller with the increase of pump energy. An unusual pulse compression was investigated of the stimulated Brillouin scattering in water, it was found that the SBS pulse duration becomes larger as the pump energy increases. The pulse duration of SBS alters differently with the change of pump energy in strong focusing and weak focusing. Numerical simulation of pump light transmission in water cell has been made to explain the unusual pulse compression phenomena. Different real gain lengths in strong and weak focusing make different SBS pulse compression.

High-peak-power nanosecond pulse generation by stimulated Brillouin scattering pulse compression in a seeded Yb-doped fiber amplifier

We demonstrate the generation of nanosecond and multikilowatt peak-power pulses in a double-clad Yb-doped fiber amplifier seeded by a spectrally narrowed gain-switched laser diode. Injected pulses with 100 ns duration were simultaneously compressed and amplified by the combination of high amplifier gain and stimulated Brillouin scattering. A maximum peak power of 20 kW has been obtained, corresponding to a single-pass gain of +57 dB in terms of peak power. Part of this output signal was also converted into IR continuum light by splicing a length of single-mode fiber at the end of the fiber amplifier.

Development of a sub-MeV X-ray source via Compton backscattering

At the Kansai Photon Science Institute of the Japan Atomic Energy Agency, we have developed a Compton backscattered X-ray source in the energy region of a few hundred keV. The X-ray source consists of a 150-MeV electron beam, with a pulse duration of 10 ps (rms), accelerated by a Microtron accelerator and an Nd:YAG laser, with a pulse duration of 10 ns (FWHM). In the first trial experiment, the X-ray flux is estimated to be (2.2±1.0)×10 2 photons/pulse. For the actual application of an X-ray source, it is important to increase the generated X-ray flux as much as possible. Thus, for the purpose of increasing the X-ray flux, we have developed the pulse compression system for the Nd:YAG laser via stimulated Brillouin scattering (SBS). The SBS pulse compression has the great advantages of a high conversion efficiency and a simple structure. In this article, we review the present status of the Compton backscattered X-ray source and describe the SBS pulse compression system.