In this paper, we present a study on the influence of interpulse delay in laser-induced silicon plasma with femtosecond double-pulse, and two subpulses have different laser energies. The meansured optical emission line collected by a lens is the Si (I) at 390.55 nm. The range of double-pulse interpulse delay is from -150 ps to 150 ps. Unlike the femtosecond double pulses with two same energies, the combination of low + high energies can enhance the spectral emission intensity, while the combination of high + low energies probably reduces the spectral line intensity compared with single-pulse femtosecond laser. The results indicate that the interpulse delay is very important for laser-induced breakdown spectroscopy with femtosecond double-pulse to improve the optical emission intensity.
In laser-induced breakdown spectroscopy (LIBS), a serious of cylindrical cavities are used to spatially confine the plasmas produced from silicon (Si) target by using a Nd:YAG laser in air. Time-resolved spectrum of Si plasma with different diameters of cylindrical spatial cavities is measured. Compared with the plasmas generated without the confined cavity, the spectral emission intensity of plasma generated with cylindrical cavity is enhanced at a certain delay time. As the diameter of cylindrical cavity increases, the spectral emission is enhanced later in time and the enhancement becomes weaker. The result shows that the presence of the confined cavity leads to an increase in the spectral emission of plasma which is attributed to compressed plasma by the reflected shockwave.
We have optimized a femtosecond time-resolved system by the optical Kerr-gate (OKG) method to investigate characteristics of various Kerr media. Optical Kerr gating is widely used in ultrafast measurements ranging from pulse characterization to spectroscopy and microscopy. We compared the efficiencies and the temporal responses of three Kerr media CS2, benzene and GGG. We have demonstrated that benzene has fast response and low efficiency while CS2 has high efficiency and slow response. Benzene as a Kerr medium shows the most befitting characteristics in the three media.
Femtosecond pulse laser was used to induce Au/Cr double-layer metal films. The time dependence of transient relative reflectivity was measured by optical pump-probe experiment for 400 nm pump light and 800 nm probe light. The pulse width was 90 fs. The drastic changes in reflectivity were observed, and double-layer films with different thickness of Au layer leaded to different reflectivity changes. Next, a critical points model with the Drude model was proposed to describe the permittivity of Au in the 200-1000 nm range. This model was combined with a two-temperature equation to investigate optical properties and thermal response of Au/Cr double-layer metal films induced by femtosecond lasers. The simulated results provided more physical information for femtosecond laser induced double-layer metal films.