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The uncoated optical fiber has been extensively researched as an optomechanical sensor since it can achieve substance identification of the surrounding media by exciting and detecting transverse acoustic waves via forward stimulated Brillouin scattering (FSBS), yet within danger of being easily broken. Although polyimide-coating fibers are reported to allow transverse acoustic waves transmission to the coating for reaching the ambient while maintaining the mechanical properties of the fiber, it still suffers from the problems of humidity sensitivity and spectral instability. Here, we propose for the first time a robust distributed FSBS-based optomechanical sensor using an aluminized coating optical fiber. Benefiting from the quasi-acoustic impedance matching condition of the aluminized coating and silica core-cladding, aluminized coating optical fibers not only have stronger mechanical properties and higher transverse acoustic wave transmission efficiency but also has a higher signal-to-noise ratio, compared to the polyimide-coating fibers. The distributed measurement ability is verified by identifying air and water around the aluminized coating optical fiber with a spatial resolution of 2 m. In addition, the proposed sensor is immune to the external relative humidity changes, which is a preponderance for liquid acoustic impedance measurements.

A fast Brillouin optical time-domain reflectometry (BOTDR) for dynamic strain measurement is proposed and experimentally demonstrated based on the frequency-agile technique. Employing the band-pass filter and envelope detection, the spontaneous Brillouin gain spectrum can be online demodulated in the time domain for a truly distributed, one-end-access and dynamic strain measurement. A strain sampling rate of 62.5 Hz is achieved for the proposed sensor over 172 m single-mode fiber with 100 sweeping frequencies and 64 times of averaging. In the experiment, the vibration frequencies of 6.82 Hz and 14.77 Hz have been measured with 2 m spatial resolution and 4000 μϵ dynamic range. The measurement accuracy is calculated to be ±30 μϵ by the standard deviation of the static fiber Brillouin frequency shift. Furthermore, the performance on the strain sampling rate and measurement accuracy is investigated with different averaging times. It should be noted that the upgraded schemes for the frequency-agile based Brillouin optical time-domain analysis can be also introduced into the proposed fast BOTDR.

A wide-dynamic-range and high-resolution optical fiber sensor based on Brillouin and Rayleigh scattering is proposed, which merges frequency-scanning phase-sensitive optical time-domain reflectometry (Φ-OTDR) and Brillouin optical time domain analysis (BOTDA) via an adaptive signal corrector (ASC). The ASC suppresses the accumulated error of Φ-OTDR with the reference of BOTDA, which breaks through the measurement range limitation of Φ-OTDR so that the proposed sensor can perform a high-resolution measurement in a wide dynamic range. Its measurement range is determined by BOTDA, and can reach the limitation of optical fiber, while the resolution is limited by Φ-OTDR. In proof-of-concept experiments, a maximum strain variation of up to 302.9 µɛ is measured with a resolution of 5.5 nɛ. Furthermore, with an ordinary single-mode fiber, high-resolution dynamic pressure monitoring in the range from 20 MP to 0.29 MPa is also demonstrated with 0.14-kPa resolution. This research represents the first time, to the best of our knowledge, that a solution for merging data from a Brillouin sensor and a Rayleigh sensor which achieves the advantages of the two sensors at the same time has been realized.

The uncoated single-mode fiber has been extensively researched as an opto-mechanical sensor since it can achieve substance identification of the surrounding media by exciting and detecting transverse acoustic waves via forward stimulated Brillouin scattering (FSBS), but it has the danger of being easily broken. Although polyimide-coated fibers are reported to allow transverse acoustic waves transmission through the coating to reach the ambient while maintaining the mechanical properties of the fiber, it still suffers from the problems of hygroscopic property and spectral instability. Here, we propose a distributed FSBS-based opto-mechanical sensor using an aluminized coating optical fiber. Benefiting from the quasi-acoustic impedance matching condition of the aluminized coating and silica core cladding, aluminized coating optical fibers not only have stronger mechanical properties and higher transverse acoustic wave transmission efficiency but also have a higher signal-to-noise ratio, compared with the polyimide coating fibers. The distributed measurement ability is verified by identifying air and water around the aluminized coating optical fiber with a spatial resolution of 2 m. In addition, the proposed sensor is immune to external relative humidity changes, which is beneficial for liquid acoustic impedance measurements.

In this study, surface-enhanced Raman spectroscopy (SERS) technology was used to rapidly detect illegally added sildenafil drugs. A detailed attribution analysis by density functional theory (DFT) was used to guide specific experiments. The Raman signals were obtained from a silver colloid (Ag col) substrate, and they increased in the presence of the mineral salt, potassium iodide (KI). These methods detected sildenafil in aqueous solutions as low as 1 µg/mL with high signal uniformity (RSD=3.77%). Prior to this study, traditional Raman techniques detected substances in solid samples only. Here, Raman technology detected low contents of sildenaful drugs in liquid nutraceuticals. Therefore, SERS technology has great potential for on-site and real-time detection of illegal drugs in water and in liquid nutraceuticals.

A new stimulated Brillouin scattering (SBS) compression mechanism, quasi-steady-state SBS compression, in which the compression limit is one-tenth of the phonon lifetime with a high energy efficiency, is proposed and practically realized in this study. The feasibility of this approach is demonstrated experimentally, in which a compression of 0.36τB with an energy efficiency of 65% is achieved in a 3M Fluorinert Electronic Liquid FC-3283 and a compression output of 0.12τB (near-compression-limited) with an energy efficiency above 40% is obtained in acetone when the phonon lifetime to leading-edge to ratio is greater than 10. This ratio is identified experimentally as the key parameter in quasi-steady-state SBS compression. This work provides a practical approach to reliably generating one-tenth-phonon-lifetime pulses by quasi-steady-state SBS compression.

Stimulated rotational Raman scattering (SRRS) limits the effective transmission distances of the high-energy and high-power laser pulses in laser–fusion systems and other applications. A simple and practical method of suppressing SRRS process by controlling the polarization direction of Stokes light is proposed. For a narrowband, linearly polarized, flat-topped laser pulse of 351 nm with intensity of 2 GW/cm2 and width of 3 ns, the SRRS threshold distance in air is lengthened to 30.0 m from 16.2 m easily using the method. Simulation results demonstrate that the method is also applicable for broadband laser.

Surface-enhanced Raman spectroscopy (SERS) was used for detecting Rhodamine B (RB) which is often added illegally to chili powder. Based on density functional theory, the Raman spectrum of RB was calculated and characteristic peaks of RB were assigned to the corresponding vibrational modes. RB was detected utilizing paper-based SERS substrates which were fabricated via a liquid–liquid interface-mediated self-assembly technique. Meanwhile, with simple sample pretreatment, the detection limit could reach 10−6 g g−1 for RB in chili powder (5 × 10−7 g mL−1 in extraction agent). Within the concentration range from 10−2 g g−1 to 10−6 g g−1, Raman intensity follows a certain function in relation to the concentration of RB. The recovery of this method ranges from 96.4% to 108.9%, which gives rapid and reliable quantitative detection of RB in chili powder. Therefore, the proposed SERS method is suitable for on-site detection and analysis of RB in chili powder.

Dicyandiamide (DCD) is a contaminant found in New Zealand's milk supply, which needs to be examined for security. In this study, the feasibility of using a SERS technique to detect DCD in milk was evaluated. Assignments of the DCD vibrational spectra have been conducted by DFT calculations. The influences of different aggregating agents and pH have been investigated in terms of their efficiency for detecting DCD. Two detection modes were established for detecting DCD in an aqueous solution. Among the three ions, SO42− provides the best performance in both acidic and alkaline conditions, and the limit of detection in alkaline conditions (with an enhancement factor of 2.88 × 105) is lower than that under acidic conditions. For real milk samples, based on a particular order of agent addition, DCD can be quantitatively detected without any sample pretreatment through an internal standard method. The linear coefficient is 0.99747 at a concentration range from 1 × 10−4 to 1 × 10−3 g mL−1. By exploiting the multi-component detection ability and high sensitivity of SERS, our scheme has advantages such as simplicity, reduced time and good accuracy over other methods, which shows a great promise for the on-site screening of DCD in milk products.

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.

A portable Raman spectrometer was used for the rapid detection using surface-enhanced Raman spectroscopy (SERS) of pethidine hydrochloride injection by employing a silver colloid as the SERS active substrate. Different substrates and aggregation agents were investigated in order to explore the optimum conditions for the SERS detection of pethidine hydrochloride injection. Under the optimum experimental conditions, excellent reproducibility and stability of SERS detection was guaranteed. In addition, the limit of detection (LOD) for pethidine hydrochloride injection in water was low at 0.1 μg mL−1 with an analytical enhancement factor of 5.3 × 104, which is extremely far below typical administered dosages (50 mg mL−1). Finally, a good linear relationship between the Raman intensity and concentration was obtained for pethidine hydrochloride injection in water at a concentration range from 0.1 to 10 μg mL−1 (R2 = 0.999), which lays a favourable foundation for the semi-quantitative analysis of the concentration of pethidine hydrochloride injection. In general, the capabilities reported here demonstrate that the SERS method is convenient, rapid and efficient, and has good potential in clinical applications for point-of-care detection and real-time monitoring.

In this work, a robust and easy-to-handle strategy was developed to fabricate silver nanoparticles (Ag NPs)-decorated filter paper as surface-enhanced Raman spectroscopy substrate using dip-coating method only with the assistance of chloride ions. Filter paper was modified with chloride ions for chemisorption of Ag NPs, overcoming the electrostatic repulsion between Ag NPs and paper. The effect of laser-induced substrate deformation was studied. The enhancement factor of the substrate was higher than 6.4 × 105 with a limit of detection of 1 × 10−8 M for 4-mercaptobenzoic acid. The Ag NPs-decorated paper substrate exhibits a good uniformity and can be stored for more than 2 months with negligible degradation. This substrate has great potential for detecting food contaminations, environment polluters and biomolecules.

In order to achieve the truncated amplified spontaneous emission pulse, the method of timeshare quenching was proposed in this paper. When the original pulse of the amplified spontaneous emission is 16.72 ns, the obtained best results show that the pulse width is truncated to 2.48 ns, and the shortening ratio is approximately 6.7. By analyzing the 12 acquisition results of the continuous amplified spontaneous emission truncation, 2.59 ± 0.05 ns amplified spontaneous emission pulse was obtained. The experimental results showed that the stability of the truncated pulse width is well. This method is applicable to truncate the ASE pulse in KrF excimer laser. It is significantly to the research of the inertial confinement fusion.

Surface-enhanced Raman spectroscopy (SERS) was used for rapid detection of sodium thiocyanate in milk employing silver aggregates as active substrate. Silver nanoparticles were induced to silver aggregates by trichloroacetic acid (TCA). The limit of detection (LOD) for sodium thiocyanate was 10−2 µg ml−1 in water with an analytical enhancement factor of 5.4 × 106. The silver aggregates represent good reproducibility and stability. Good linear relationship was obtained for sodium thiocyanate in milk at concentration ranges from 0.1 to 10 µg ml−1 (R2 = 0.995). Using TCA as protein precipitator, silver colloid would aggregate spontaneously when mixing with samples during SERS measurement without the need of additional aggregating agent. The simple pretreatment procedures and analytical methods are less time consuming (

An excellent paper-based SERS substrate was easily fabricated by utilizing interfacial films formed in the mixture of Ag colloid and CH2Cl2. This interfacial film coating method significantly improves the fabrication efficiency of SERS substrates. The substrate has a high coverage of silver nanoparticles (Ag NPs) and can be tailored to arbitrary shapes. The SERS substrate exhibits high sensitivity (EF ∼ 4 × 107) and gives uniform SERS signals with a relative standard deviation (RSD) of 8.08% (spot-to-spot) and 8.65% (batch-to-batch) using 4-mercaptobenzoic acid (4-MBA) as a Raman probe. In addition, this SERS substrate with excellent stability can be stored for more than 30 days. The limit of detection was found to be 10−8 M for 4-MBA. In general, this SERS substrate is qualified for rapid and simple trace detection of various analytes.

A new droplet configuration was developed to simplify and optimize the SERS detecting condition using silver colloid as SERS substrate. Samples were measured in solution to improve the evenness of SERS response. The influences of the reflectivity of substrates and height of sample solution on Raman intensity have been studied systematically. Aluminum tape was employed as the supporting platform for SERS detection. Based on the high reflectivity and hydrophobicity of aluminum tape, this configuration is both highly efficient and convenient. The detection limit of melamine is 10−2 ppb in water and the distribution of SERS intensity is regular over the droplet profile with good reproducibility. Under this configuration, melamine in milk can be quantitatively detected without any sample pretreatment in a special order of agent addition. A good linear relationship was obtained at concentrations ranging from 0.05 to 10 ppm (R2 = 0.9963). Our scheme has advantages such as simplicity, improved reproducibility, less time and good accuracy over other methods, which offers tremendous potential for the on-site examination of trace melamine in three types of milk (pasteurized milk, skimmed milk, sweet milk).

It is necessary for high power ultraviolet lasers to propagate through a long air path during experiments of inertial confinement fusion (ICF). When the product of gain efficiency and propagation distance is beyond the stimulated rotational Raman scattering (SRRS) threshold, the high power ultraviolet laser beam is subject to loss of energy and a decrease in beam quality, further resulting in the reduction of conversion efficiency of triple-harmonic, and even causing the optical components to be destroyed. This paper studies the four-dimension numerical modeling of SRRS effects, with emphasis on the variation of beam aperture and corresponding beam distributions in near field. The research showed that the variation of the pump beam aperture made little effect on SRRS transform efficiency ratio with the same incident energy and the same propagation distance, the transverse intensity distribution of beams became more even with an increase in the beam aperture. We have made the deduction that high power laser's SRRS effects through a long air path could be depressed by increasing the beam aperture on the condition of equal incident energy and propagation distance.

This 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%.

The effect of smoothing by spectral dispersion (SSD) on stimulated rotational Raman scattering (SRRS) in air has been investigated both numerically and theoretically. The suppression effect of SSD on SRRS process is verified and it is demonstrated and proposed that the suppression effect is attributed to two aspects: the decreasing of the laser fluence modulation degree and the reducing of Stokes gain coefficient caused by the temporal and spatial variation of the phase of the incident laser pulse. The simulation results show that the SRRS threshold distance can be lengthened by choosing appropriate SSD parameters.

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 1064 nm, 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 8 ns laser pulse of 1064 nm generated by Q-switched Nd: YAG was optimally compressed to 116 ps for pump energies of 310 mJ, while the energy reflectivity is above 85%. The shortest pulses width obtained exhibit 99 ps 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.

This paper demonstrates that the stimulated rotational Raman scattering (SRRS) threshold for high peak power laser pulses propagating through a long air path can be influenced strongly by the near-field quality of the laser beams, and the relationship between the SRRS threshold and the near-field beam quality (i.e., spatial intensity modulation index and contrast ratio) can be evaluated quantitatively. By using our three-dimensional numerical model, which can describe the spatial–temporal evolution behaviors of SRRS and is verified by previously published SRRS experimental data, the criteria of the safe transmission distance for high peak power nanosecond laser pulses are obtained, and the modified SRRS threshold criterion formulas considering the near-field beam conditions are presented.

In this paper, we designed an experiment to research the properties for the stimulated Brillouin scattering (SBS) medium of perfluorocarbon-compounds (PFCs) and perfluoropolyether (PFPE), then we proposed that the selection principle of the high load capacity SBS medium can be used in the high peak power SBS system. The results showed that, for PFCs, perfluorinated hydrocarbons (FC-72) has the highest optical breakdown threshold (OBT); for PFPE, the medium with average molecular weight (AMW) less than 1000 has small medium absorption coefficient (AC) and high OBT, for AMW, greater than 1000, the medium AC becomes high and the OBT becomes low. Further research shows that, for PFPE series SBS medium, the AC increases and the OBT decreases gradually with increasing of AMW. We find some SBS mediums can work stably under high peak power pump, which lays a good foundation for the application of SBS technology in a high-power laser system.

The performances of stimulated Brillouin scattering (SBS) media with short phonon lifetimes on temporal compression are studied in this paper. In the experiment, FC-72, HT-135 and FC-40 (phonon lifetimes are 1.2 ns, 0.4 ns and 0.2 ns, respectively) are used to study the influence of phonon lifetime on pulse compression in a compact two-cell SBS system. High pulse compression ratio is obtained by a medium with a short phonon lifetime when input energy is high. These results are useful in the generation of picoseconds pulse for Shock Ignition of thermonuclear fuel for ICF.

The current trends in stimulated Brillouin scattering and optical phase conjugation are overviewed. This report is formed by the selected papers presented in the “Fifth International Workshop on stimulated Brillouin scattering and phase conjugation 2010” in Japan. The nonlinear properties of phase conjugation based on stimulated Brillouin scattering and photo-refraction can compensate phase distortions in the high power laser systems, and they will also open up potentially novel laser technologies, e.g., phase stabilization, beam combination, pulse compression, ultrafast pulse shaping, and arbitrary waveform generation.

A non-collinear laser beam combination based on Brillouin amplification is proposed. The influence of non-collinear Brillouin amplification on the combination efficiency is analyzed and discussed theoretically. It is shown that an efficiency of 80% can be achieved with the angle between the Stokes and the pump limited to a range of 10°. The theoretical prediction is tested in experiment of non-collinear amplification of one Stokes and one pump. A two-beam combination scheme is designed and a high combination efficiency of 80% is also obtained in this experiment. According to these results, a 20-beam combination scheme is designed to achieve 13.2-J output energy. A very simple construction for a multiple beams combination is designed.

The effect of medium temperature upon characteristic of stimulated Brillouin scattering (SBS) and SBS optical limiting is investigated. The physical mechanism behind is analyzed theoretically and experimentally verified in Continuum's Nd: YAG Q-switched laser system using FC-72 as the SBS medium. The temperature affects the electrostrictive coefficient, refractive index, density and acoustic velocity of the medium weakly. In contrast, the kinematic viscosity, which is inversely proportional to the temperature, is related to gain coefficient and phonon lifetime and thus greatly affects the SBS characteristics. Therefore, in the low temperature, the kinematic viscosity is usually high, which can lead to a small gain coefficient and a short phonon lifetime. Therefore, the SBS characteristic can be changed by controlling the temperature to a great extent.

In order to improve the optical limiting performance based on stimulated Brillouin scattering (SBS), a combination of SBS and carbon nanotube/HT-270 suspension for optical limiting is proposed in this paper. The dependence of output energy of optical limiting based on this hybrid approach on the pump energy is numerically simulated, and validated in Continuum's Nd: YAG seed-injected laser. The results indicate that the output energy based on this hybrid approach shows much better performance compared with that based on single SBS. In this approach, the SBS threshold can be controlled by adjusting the gain coefficient of medium and focal length of the lens, and the threshold of suspension can be controlled by altering the concentration and focal length of the lens, therefore, this hybrid approach to realize optical limiting has great potential in practical application.

A method of generating flat-top waveform in the time-domain based on stimulated Brillouin scattering (SBS) using medium with short phonon lifetime is proposed. In theory, the transmitted pulse is simulated in the case of several media with different phonon lifetime. In experiment, FC-72 and HT-270, which differ significantly in the phonon lifetime, are exploited in the experiment. Both the theoretical and experimental results indicate that, when choosing medium with short phonon lifetime, the top is almost a platform, while there is a peak in the front and a platform thereafter when choosing medium with long phonon lifetime.

An overview on current trends in stimulated Brillouin scattering and optical phase conjugation is given. This report is based on the results of the “Second International Workshop on stimulated Brillouin scattering and phase conjugation” held in Potsdam/Germany in September 2007. The properties of stimulated Brillouin scattering are presented for the compensation of phase distortions in combination with novel laser technology like ceramics materials but also for e.g., phase stabilization, beam combination, and slow light. Photorefractive nonlinear mirrors and resonant refractive index gratings are addressed as phase conjugating mirrors in addition.

A 100-J-level Nd:glass laser system in nanosecond-scale pulse width has been constructed to perform as a standard source of high-fluence-laser science experiments. The laser system, operating with typical pulse durations of 3–5 ns and beam diameter 60 mm, employs a sequence of successive rod amplifiers to achieve 100-J-level energy at 1053 nm at 3 ns. The frequency conversion can provide energy of 50-J level at 351 nm. In addition to the high stability of the energy output, the most valuable of the laser system is the high spatiotemporal beam quality of the output, which contains the uniform square pulse waveform, the uniform flat-top spatial fluence distribution and the uniform flat-top wavefront.

A transparent SERS platform was fabricated via the gel-trapping method coupled with a liquid/liquid interface self-assembly technique. We employed gold nanorods as the building blocks for interface self-assembly because of their strong localized surface plasmons upon excitation by infrared radiation. Based on a "top cover" configuration, this transparent SERS platform endows high signal reproducibility for directly detecting liquid samples by confining the sample droplet into a regular shape. The Au NR PDMS platform was able to directly detect crystal violet in aqueous solutions down to 10 ppb level with high enhancement factor (0.87 × 10(5)) and signal uniformity (RSD = 3.9%). Furthermore, SERS-based anti-fungal agent detection on a fish scale was demonstrated by simply covering the fish scale with a tailored GNRs PDMS film. The experimental results clearly show that the Au NR PDMS SERS platform has great potential for on-site real time detection of contaminants in water as well as on curved surfaces.

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.

A laser pulse temporal compression technique combining stimulated Brillouin scattering (SBS) and laser-induced breakdown (LIB) is proposed in which the leading edge of the laser pulse is compressed using SBS, and the low intensity trailing edge of the laser pulse is truncated by LIB. The feasibility of the proposed scheme is demonstrated by experiments in which a pulse duration of 8 ns is compressed to 170 ps. Higher compression ratios and higher efficiency are expected under optimal experimental conditions.

Using the method of optical breakdown clipping on Krypton Fluoride excimer laser, ASE (Amplified Spontaneous Emission) pulse compression technology was studied in this paper. And the liquid medium breakdown depth on the ASE pulse compression effect was analyzed. The initial ASE pulse width was16.8ns, the shortest 8.4ns ASE pulse was obtained in the experimental. The auxiliary beam induced luminescence breakdown was used to study on the law of optical breakdown clipping, and the short 7.3ns ASE pulse was got. These experimental results proved that the auxiliary beams are useful to accelerating the plasma generation rate and duration. The results ASE pulse compression can be controlled in some degree.

The influence of focal length on optical limiting power characteristics based on stimulated Brillouin scattering in CCl4 medium is investigated numerically and experimentally. The simulation results show that, the characteristics of limiting power and pulse shape are controlled mainly by focal length when other parameters are fixed. When focal length is short, for example 5cm, the characteristic of limiting power and pulse shape is close to ideal. In experiment, focusing 8ns, 1064nm, 16mJ pulses into CCl4 medium, the rules of limiting power and pulse shape versus focal length are investigated. The experimental results are in good agreement with the conclusions of theoretical simulations.

Focusing Q-switched laser pulses into FC-72 medium, the transverse profiles and spatial evolution of beam in stimulated Brillouin scattering (SBS) are investigated experimentally by CCD camera and digital image processing technology, and the rules of spot size versus pump energy are obtained. The results show that the transverse profiles of backward SBS spots with different pump energies are Gaussian or quasi-Gaussian profiles when pump beam is Gaussian. And the spatial profiles of SBS spots change from quasi-Gaussian to Gaussian when the incident energy increases from the threshold to several times the threshold. At the same time, the size of SBS spot decreases with the increasing pump energy on the whole.

Focusing Q-switched laser pulses into FC-72 medium, the transverse profiles and spatial evolution of backward stimulated Brillouin scattering (SBS) beam are investigated experimentally by CCD camera and digital image processing technology.

Adopting noise initiation mode of stimulated Brillion scattering (SBS), the influence of phonon lifetime and gain coefficient of medium on power limiting characteristic is numerically investigated. By using actual parameters of three media, CCl4, Acetone, and CS2, the waveforms of transmitted pulses are simulated. It shows that, different media have little effect on the front peak of waveform, while have an obvious effect on the height of power limiting platform. When using the medium which has short phonon lifetime and small gain coefficient, the height of power limiting platform is comparatively high. When using the medium which has long phonon lifetime and large gain coefficient, the height of power limiting platform is comparatively low. In experiment, focusing 1064nm, 8ns, 18mJ pulses into these three media respectively, the waveforms of transmitted pulses are obtained. And it is shown that, the experimental results are in good agreement with the conclusions of theoretical simulations.© (2007) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

It is investigated that the duration of stimulated Brillouin scattering (SBS) amplification of Stokes pulses is smaller than the acoustics lifetime and the oscillation period of hypersound with the nanosecond pulse as pump light. In the experiment, the Fluorinert (FC-72) is used as the Brillouin amplification medium, the Stokes pulse duration less than 1/4 of oscillation period of hypersound of FC-72 as seed pulse is achieved by two-stage SBS compressor to compress 8ns laser pulse. The experiment and simulation show that, in this case, their energy amplification is efficient, but the duration of amplified pulses is longer than the initial seed pulse. Simulation results of higher energy than the maximum energy in the experiment show that at sufficient high pump or initial seed pulse power intensity, the duration of amplified pulses can be no larger than the initial seed pulse duration., even less than the seed pulse duration.

Serial coherent laser beam combination is studied using one-dimensional transient model of stimulated Brillouin scattering (SBS). Beam combination is achieved by transferring the energy of several pump beams to one Stokes beam. The pulse-width of the Stokes beam, which is approximately equal to that of the pump, can be kept constant by adjusting the meeting position between Stokes beam and pump beams in the cell. Numerical simulation is made for the condition that power density of Stokes beam is larger than that of the pump beam. Simulation results show that the major factors that determine the energy extraction efficiency and the critical value of beam combination are the absorption of the medium and the length of SBS cell. The absorption loss is found to play a leading role, so that the overall energy extraction efficiency and the critical value of beam combination can be increased by using shorter SBS cells and/or medium with lower absorption rate. The simulation chooses CCl4 as target medium. The SBS cell length is 20cm; 20 beams (wavelength 1064nm, energy 1J, pulse-width 10ns, beam-area 1cm2) are combined in serial, one of which generates the Stokes seed, others are the pump beams. In order to keep the power density below 100MW/cm2 to avoid being more than threshold of SBS, the Stokes beams and pump beams must be expanded. The output beam of ~10J energy, ~10ns pulse-width, ~10cm2 beam area is obtained.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Based on the multi-axial theory of stimulated Brillouin scattering (SBS), a group of coupled wave equations without limitation to the mode separation of a laser is deduced when the random initial phases of the axial modes are introduced for SBS pumped by a free operation laser. The coupling coefficient between two axial modes is obtained, and the dependences of the threshold and reflectivity of broadband SBS on the bandwidth, the mode number, the mode separation of the laser, are simulated numerically. The SBS threshold and reflectivity are dependent not only on the laser bandwidth, but also on the mode number and the mode separation of the laser.

A 1.5m long cell, different focusing lens, a KrF laser which bandwidth is 0.5cm-1, and SF6 gas as Brillouin medium are used in the experiment. The influences of focus length and SF6 pressure on threshold of stimulated Brillouin scattering excited by broadband KrF laser were investigated, respectively. The SBS threshold increases with increasing of the focus length and decreasing of the SF6 pressure. The results show that the threshold of broadband SBS is various with the different focus length and SF6 pressure. For more precisely to explain the experimental results, a novel model considering optical breakdown and pump linewidth was presented. The model we proposed here assumes that the KrF laser spectrum is made up of a seriues of narrowband spectra, each generating one Stokes wave. In addition, it is assumed further that the neighbors of one narrowband spectrum also contribute to the generation of its corresponding Stokes wave to some degree. Optical breakdown is assumed to lead to the loss of pumping energy only. The experimental results are consistent with the numerical theory.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A 1.5m long cell, different focusing lens, a KrF laser which bandwidth is 0.5cm-1, and SF6 gas as Brillouin medium are used in the experiment. The influences of SF6 pressure on threshold, energy reflectivity and pulse compression of stimulated Brillouin scattering excited by broadband KrF laser were investigated, respectively. For more precisely to explain the experimental results, a novel model considering optical breakdown and pump linewidth was presented. Optical breakdown is assumed to lead to the loss of pumping energy only. The experimental results are consistent with the numerical theory.