Using the model of index variation and mode coupling theory,first and second order diffraction spectra of fiber Bragg gratings after saturation are simulated. Bragg wavelength shifts and the changes of maximum reflectivity during the formation of fiber Bragg gratings versus the variation of saturation coefficient are also simulated.

It is found that the contribution of second order diffraction potential to second order wave forces is important, The effect of water depth and submerged depth on the wave force is also discussed.

Two dimensional diffraction problem for multiple horizontal cylinders of the second order Stokes waves is treated in frequency domain based on the boundary element method using simple Green's function in inner water region combined with the eigenfunction expansions in outer water regions. The analytical expression of second order diffraction potential in the outer regions of finite water depth gives a clear physical meaning of wave transmission and reflection characteristic in the far field.

The method suggested by reference [1] is used to calculate second order diffraction force on a vertical cylinder in regular waves. It is found that the method is effective when the product of the water depth and the wave number is larger than 2.5 and that the result is instable when the product of water depth and the wave number is less than 2.5, In the latter case we must improve the method to obtain an approximative solution.

Significant distortions in measured X-ray absorption fine structure occur when there are impurities' emission lines on the continuum spectra m the investigated energy range. A method for correcting that distortion is proposed. As the EXAFS amplitude decreases, which is caused by the application of second order diffraction of a monochrometer, how to obtain correct structural parameters is also discussed.

The second order diffraction problem of Stokes waves around a vertical circular cylinder in finite water depth is studied by dividing it into four boundary value problems. The solutions satisfying all boundary conditions have been obtained.

The second order diffraction light of Rayleigh scattering light,Raman light,diffused light and the fluorescence diffracted from the grating have been discussed.

Non-linear wave forces on fixed or floating offshore structures have attracted much attentions recently. This paper deals with the non-linear effects of regular waves on fixed two-dimensional bodies up to secondorder terms. The second-order diffraction potential is solved consis tently and the second-order steady wave forces and the biharmonic wave forces with frequency corresponding to the double of the incident wave frequency are obtained.By use of the strip theory, this method...

Non-linear wave forces on fixed or floating offshore structures have attracted much attentions recently. This paper deals with the non-linear effects of regular waves on fixed two-dimensional bodies up to secondorder terms. The second-order diffraction potential is solved consis tently and the second-order steady wave forces and the biharmonic wave forces with frequency corresponding to the double of the incident wave frequency are obtained.By use of the strip theory, this method and the results may be used to predict the second-order wave forces on ships or some submersible platforms.

Many investigations have been made recently on nonlinear wave diffr-action problems for three-dimensional bodies.However,even for the simp-lest configuration such as single seabed mounted,surface piercing verticalcircular cylinder,it is still worthwhile to investigate into strict solutionfor second-order diffraction potential and corres-ponding second-order wa-ve forces exerted upon cylinders.On the basis of analysing the mechanism of generation of second-or-der diffraction...

Many investigations have been made recently on nonlinear wave diffr-action problems for three-dimensional bodies.However,even for the simp-lest configuration such as single seabed mounted,surface piercing verticalcircular cylinder,it is still worthwhile to investigate into strict solutionfor second-order diffraction potential and corres-ponding second-order wa-ve forces exerted upon cylinders.On the basis of analysing the mechanism of generation of second-or-der diffraction potential,an exact solution is proposed in this paper.Thenonlinear wave forces on a vertical circular cylinder calculated by thepresent method have shown good agreement as compared with experiment-al results.Various effects of components of second-order potential on thenonlinear forces are also discussed in this paper.

The emission spectra of Nd0.9La0.1P5O14 (NLPP) crystal have been measured at 40K(see Fig.1).We found four series emission lines: at-0.9μm due to 4F3/2-4I9/2 transitions of Nd3+ ions, -l.05μm due to 4F3/2-4I1 1/2 transitions, and-1.35μm to 4F3/2-4I1 3/2 transitions.The lines at-1.8μm have been proved to be the second order diffraction of the 4F3/2-4I9/2 transitions, although the lines of 4F3/2-4I1 5/2 might be expected to occur in this region.Fig.2 shows the fine structure of 4F3/2-4I1 1/2 transitions in...

The emission spectra of Nd0.9La0.1P5O14 (NLPP) crystal have been measured at 40K(see Fig.1).We found four series emission lines: at-0.9μm due to 4F3/2-4I9/2 transitions of Nd3+ ions, -l.05μm due to 4F3/2-4I1 1/2 transitions, and-1.35μm to 4F3/2-4I1 3/2 transitions.The lines at-1.8μm have been proved to be the second order diffraction of the 4F3/2-4I9/2 transitions, although the lines of 4F3/2-4I1 5/2 might be expected to occur in this region.Fig.2 shows the fine structure of 4F3/2-4I1 1/2 transitions in NLPP (see Fig.2(b)), compared with the same transitions of Nd3+ in NdP5O14 (Fig.2(a)(c), Ref.[1])and Nd:YAG crystals (Fig.2(d), Ref.[7]).In this way we could identify the each line around 1.05μm with the transitions between the Stark levels of 4F3 2 and 4I1 1/2.The strongest fluorescence line at 1.051μm in NLPP,which can become stimulate radiation at proper conditions, comes from the transition of lower Stark level of 4F3/2 to 4I1 1/2.While in Nd:YAG, the strongest emission line at 1.064μm, which can be transformed to lasering line at above room temperature, comes from the transition of upper Start level of 4F3/2 to 4I1 1/2. This is the major difference of the two lines of Nd3+ in NLPP and Nd:YAG crystals. We therefore measured the temperature dependence of the two lines in a wide temperature range (77-500K), (see Fig.4). For NLPP, the intensities of l,051μm fluorescence decrease monotonicly with the increase of temperature, However for Nd:YAG, the intensities of 1.064μm fluorescence increase with the rise of temperature until 420K, then decrease. we understand this phenomenon in the light of the different transition mechanism of Nd3+ in the two crystals. In NLPP. with the increase of temperature, the population in the lower Stark level of 4F3/2 would bs thermally released to upper Stark level of 4F3/2, resulting in the quenching of the 1.051μm line with temperature,In Nd:YAG, the release of the population in the lower Stark level to upper level of 4F3/2 will enhance the fluorescence between the transition of upper Stark level of 4F3/2 to 4I1 1/2, which is just the 1.064μm emission line.Above 420K, the thermal quenching will start in the upper Stark level of 4F3/2 in Nd:YAG, so the intensities of 1.064μm luminescence turn to decrease. The measurements of the temperature dependence of each line will help us to understand the optical transition processes.