Qihong Lou

Experimental study of enhanced emission of the laser-ablated plume in backing gas

The effects of background gases on the optical emission of the excimer-laser-ablated plume from a brass target have been studied experimentally. It is found that the plume emission can be enhanced significantly in a proper gas ambient. In hydrogen, the highest peak intensity is detected, and in argon, there is a distinctive difference in the pressure-dependent emission between in He and in the other three gases, Ar, N2 and H2. Moreover, the monitored line peak intensity remains unchanged in Ar and N2 and increases in H2 within a distance above the target surface; but in He, the observed peak intensity decreases with distance like in vacuum. Furthermore, the emissions of several more atomic lines of Cu and Zn atoms from the plume are also found to be enhanced in the same manner in gas ambient. Some physical processes involved in the plume expansion and the possible mechanisms for the enhanced emission of the plume in backing gas are discussed.

Efficient XeCl/H2 Raman shifting to a blue‐green region

90% photon conversion of 18 MW (1 J, 55 ns) power XeCl laser radiation to Raman Stokes beams is reported with 39% photon efficiency and ∼60% peak power conversion efficiency to the third Stokes order S3 (499 nm). Relaxation oscillations of higher order Si(i≥3) pulses have been observed.

The effect of specific input energy on the performance of an X-ray preionised XeCl discharge laser

Abstract The input energy of a self-sustained discharge laser has an optimum value related to the discharge volume and total gas pressure. In this paper, the effect of specific input energy on the performance of an X-ray preionised XeCl discharge laser was calculated by using a simplified kinetic model of the XeCl laser.

Investigation of the Raman wavefront of higher order gaussian-hermite modes

Abstract The structures of the Raman wavefront of various higher order gaussian-Hermite modes have been investigated for the first time. The edge intensifying, gain focusing and spatial spectrum narrowing of the Stokes beams resulting from the effects of diffraction and secondary Stokes wave process, have been discussed in detail.

Excimer-laser-induced permanent electrical conductivity in solid C60 films

After being irradiated in air by a XeCI (308 nm) excimer laser, the electrical conductivity of solid thin-film C60 has been improved by more than six orders of magnitudes. The products resulting from laser irradiation of C60 films have been investigated by Raman scattering and the onset of conductivity can be attributed to laser-induced oxygenation and disintegration of the fullerene. Irradiated by ≈ 40 ns laser pulses with different fluence, products with different microstructure were observed. At lower fluence, the Raman features of microcrystalline graphite and fullerene polymer were observed. At a fluence just below the ablation threshold (36 mJ/cm2), the fullerene molecules in the film were disintegrated completely and transformed to amorphous graphite.

Beam-deflection study of shock wave formation and propagation in gas ambient during uv laser ablation of solid material

Abstract Beam-deflection technique has been used to detect the propagation of both the plume and the shock wave during laser pulse ablation of materials. It is shown that the shock wave formation differs in different gas ambient. The measured plume expansion velocities follow the exp(-α x ) law with increasing distance from the target surface, while the velocities of the shock wave agree with the propagating theory of the shock wave in a homogeneous gaseous medium.

Synthesis of nanometer Nd glass particles by excimer laser ablation and research on its spectrum

In this experiment, a XeCl excimer laser was used for ablation of Nd glass material. The powders that sprinkle from the target were collected. The size distribution of ultrafine particles are analysed at different laser fluences. The absorption and fluorescence spectrum show that there are many differences between bulk material Nd glass and nanometer powder.

Passive mode-locking of a Nd:YAP laser at 1.3414 μm by using a convex-antiresonant ring unstable resonator

Abstract The colliding pulse mode-locking of Nd:YAP lasers which have a plane-convex unstable resonator was investigated at 1.3414 μm. The experimental results showed that the mode-locked output energy reached 57.3 mJ (the biggest pulse in the pulse train was more than 8 mJ), with pulse duration of 78.7 ps. The stability of the dye solution was also investigated.

Stimulated collision-induced fluorescence and stimulated Raman scattering in barium vapor pumped by XeCl laser radiation

Abstract Stimulated collision-induced fluorescence at wavelengths of 472.6, 582.6 and 648.3 nm was observed in Ba-He mixture, pumped by XeCl laser radiation. While the SCF intensity is increased with He buffer gas pressure, the SRS intensity is decreased significantly. The strong competition between 582.6 nm and 648.3 nm SCF was observed. The SCF at 582.6 nm has lower threshold, but the 648.3 nm emission dominates at high pump intensity.

Laser-induced damage threshold of thin film in a gas chamber

The damage threshold of ZrO2/SiO2 and HfO2/SiO2 thin films was investigated in gas chamber (with oxygen gas, air, helium gas or vacuum condition) by using a scattering detector system. The experimental results show that the damage threshold is increased about 20% in oxygen gas ambient. The mechanism of these phenomena is discussed.