We present an experimental and theoretical study of energy transfer from a wide-band supercontinuum to narrow-band second harmonic light during propagation of a femtosecond pulse in a MgO:LiNbO(3) crystal. The energy removed from the supercontinuum at 1038 nm by phase-matched second harmonic generation is compensated by energy transfer from other wavelengths within the supercontinuum by self phase modulation via the Kerr effect.

Temperature measurements have been carried out on a 17.5 ton experimental steel casting to determine the thermophysical properties of sand mold for heavy steel castings. The determined thermophysical data are used in the solidification simulation to predict shrinkage porosity in a 300 ton lower cross-head casting of rapid forging press. Results demonstrate that the thermal conductivity of sand mold is the minimum at 400 ℃, while the increase of the specific heat with temperature slows down after 600 ℃. Furthermore, the optimization of chill and padding design leads to desirable feeding which eliminates the shrinkage cavity and porosity of the lower cross-head casting.

We present an experimental investigation of a filamentation-assisted fourth-order nonlinear optical process in KTP crystals pumped by intense 1.53 eV (807 nm) femtosecond laser pulses. Femtosecond light pulses at 2.58 eV (480 nm) are generated by the fourth-order nonlinear polarization (P(4) (ω2) = χ(4) (ω2, ω, ω, ω, – ω1) E3 (ω) E* (ω1), where E(ω) corresponds to the pump frequency and E(ω1) to the supercontinuum generated through filamentation). If the system is seeded by a laser beam at ω1 or ω2 and there are spatial and temporal overlaps with the pump beam, E(ω1) and E(ω2) are simultaneously amplified. When the intensity of the seed laser beam exceeds a certain intensity threshold, the contribution of P(4) (ω) = χ(4) (ω, ω1, ω2, – ω, – ω) E (ω1) E (ω2) (E* (ω))2 becomes non-negligible, and the amplification weakens. The conversion efficiency from the pump to the signal at 2.58 eV (480 nm) attains to 0.1%.

The mould filling and solidification process of the casting of 80MN rapid forging press upper beam were simulated with MAGMA.The effect of gating system design,setting of feeder,position and the size of surface chill on the solidification defect was analyzed.Basing on these results,we have predicted the position of shrinkage and porosity in the casting,and have successfully optimized the casting technique of rapid forging press upper beam.

Conical double frequency emission is investigated by femtosecond laser pulses at a wavelength of 800 nm in a DKDP crystal. It is demonstrated that the sum frequency of incident wave and its scattering wave accounts for the conical double frequency emission. The gaps on the conical rings are observed and they are very sensitive to the propagation direction, and thus could be used to detect the small angle deviation of surface direction.

A femtosecond light pulse at 480 nm in wavelength was generated during filamentation of an intense 808 nm femtosecond laser pulse propagating along the x axis and polarized between the y and z axes of a KTP crystal. It was proven that the parametric amplification process by a fourth-order nonlinear polarization (chi(4)(omega(2),omega,omega,omega,-omega(1)) induces frequency generation at 480 nm, where the pump light comes from the incident laser and the seed light comes from the generated supercontinuum by filamentation. The wavelength of the generated signal could be turned from 460 to 520 nm by adjusting the propagation direction in the crystal.

Visible femtosecond laser pulse is generated during filamentation of an 808 nm femtosecond laser pulse by a fourth order nonlinear polarization. The wavelength could be tuned from 460 to 520 nm.

Temporal evolution of absorption induced by single femtosecond pulse (130 fs, 800 nm) with high intensity in LiNbO3 is obtained using the probe shadow imaging technique in order to investigate light-induced electron relaxation processes. By saturating the polaron density with a high intensity laser pulse, ultra-fast decay process on picosecond time scale is observed. The decay time constant is about 141 ps and it is attributed to the direct interband electron–hole recombination process.