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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.

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.

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.