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We report a new structure of fiber laser, which has the advantages of temporal stability and wavelength agility. An Yb-Raman cascaded fiber oscillator generating 168 mW 1137 nm stable CW signal with 18.2% slope efficiency is demonstrated. In this fiber oscillator, the gain from both Yb ion and SRS effect is utilized. By comparison, the characteristics of the 1137 nm Yb-doped fiber laser are studied. The results show that the serious self-pulsation effect in the Yb-doped fiber laser is suppressed in the Yb-Raman cascaded fiber oscillator.

Thermal blooming anisoplanatic effect of the circular-symmetric flattened beam is analysed by the method of Gaussian beam expansion. Wave-front distortion of the thermal blooming anisoplanatic effect is expanded by the Zernike polynomials, and the Zernike coefficient and fitting error are obtained. The corrected error of the thermal blooming calculated by the numerical method is consistent with the outcome of the theoretical formula. The numerical simulation results also indicate that the angular anisoplanatic error varies proportionally to the square of the anisoplanatic angle, and the focus anisoplanatic error is in inverse proportion to the 1.71th power of the beacon height, if the caliber size is invariable.

Experimental study on all-fiber polarization maintaining master oscillator power amplifier fiber laser is performed. A 5 m small core diameter double clad polarization-maintaining Yb-doped fiber is employed in the experiment by means of two-level cascade amplification. A more than 67 W polarization maintaining laser is obtained under a maximal 88 W pump power. In this case, the laser density in the fiber core is about 3.4 W/m2, and the optical-to-optical efficiency is 76%. A higher power laser output can be realized as the pump power is further enhanced.

We present an experimental study on coherent beam combining of three watt-level fiber amplifiers using a stochastic parallel gradient descent (SPGD) algorithm. Phase controlling is performed by running the SPGD algorithm on a digital-signal-processor (DSP) chip with a voltage updating rate of 16500 times per second. Energy encircled in the target pinhole is 2.62 times more than that in an open loop. The combining efficiency is as high as 87%.

The spectral competition in pulsed dye laser is modified by semiclassical dye laser theory，showing good agreement with experimental results.Under the circumstance of interrelated competition of double-wave，the tuned spectrum is expanded by 25%.The spectrum is gradually compressed with the increasc of the coupler loss under the condition of broad spectrum width.

Stimulated Brillouin scattering(SBS) is one of important nonlinear optical phenomena, which is widely used in the areas of phase conjugation, pulse compression and beam combination. In this paper, a single axial and single transverse mode Q switched laser system is used as pump source and SBS is investigated experimentally in small bulk fused silica. Damage free operation is observed with SBS reflectivity up to 60%. The self-Stokes-seeding effect, which has been reported elsewhere, is verified. To improve reflected energy and SBS efficiency, two SBS samples connected in series is configured, but the SBS reflectivity cannot exceed 60% due to surface damage.

Traditional enthalpy probe system use the Mass Flux Controller (MFC) to measure the flux rate of sample gas. However, this method much depend on the composition of plasma working gas under the condition of steady state of sample gas inside the probe, so it takes much more time to measure the enthalpy of a point. In order to overcome the disadvantage of traditional probe, the rapid enthalpy probe system we devised measure the molar weight of sample gas by using a known volume gas container instead of MFC, making it possible to measure the enthalpy of one point in several seconds. The accuracy of result acquired by our rapid enthalpy probe system is verified through our four different experiments.

Numerical simulation was performed to study the stimulated Brillouin scattering(SBS) amplifier of self-Stokes-seeding. Chracteristic parameters such as Stokes laser,energy reflectivity,evolvement and distribution of maximum stress,pulse compression and SBS fidelity in fused silica were discussed for different Stokes ratio,wavelength,energy,pulse duration and interaction time.The focused Gaussia n pump laser was used.We got conclusions that the damage in near-front side of SBS medium was the characteristic of SBS; tuning parameters of pump laser, super -sonic stress formed in SBS process would damage the SBS medium not only on the front side, but also the damage near the focus;and the damage near the focus wo uld be made earlier when both parts were damaged.

A new stimulated Brillouin scattering (SBS) configuration, SSS(Self Stokes Seeding), is presented to describe the influence of Stokes component in a pump light on SBS process. The fast Fourier transform is used to calculate the Stokes energy ratio which denotes the ratio of the energy of Stokes component to that of total pump laser. The coupled SBS equations is solved numerically and the SSS effects is evaluated. The study shows that when the pump laser is reflected normally by the back surface of the flat sample, the Stokes component plays an important role in SBS process, such as decreasing the initiation duration. The larger the Stokes energy ratio is, the shorter the initiation duration is.

Theoretical model is established to study the Stimulated Brillouin Scattering (SBS) process with both noise initiation and seeding Stokes laser assisted initiation.Multi-steps finite difference method is adopted to solve coupled wave equations numerically, and the temporal and spatial profiles of scattered light intensity and density variations of the medium are obtained. The dependence of Stokes laser on SBS reflectivity and initiation thresholds is investigated.It is found that the time needed for SBS initiation decreases sharply since the seeding Stokes laser is introduced. Finally, the damage potential of the SBS process in optical materials is evaluated and future work is outlined.

Based on the coupled wave equations of nonlinear optics, a two-dimensional p hysics model is established to describe transverse stimulated Brilluoin satteri ng (TSBS) in large-aperture optics of a high-power laser system. The temporal and spatial profile of the stress induced by TSBS is evaluated numerically, and the damage characteristics of optical components is presented, which agrees well with the experimental phenomenon observed at LLN laboratory. The energy loss induced by TSBS are calculated to be up to 20%, sho wing that TSBS may have strong influence on routine operation of high-power las er systems.