Studies of ion energy and yield from argon clusters heated by intense femtosecond laser pulses

Using time-of-flight spectrometry, the interaction of intense femtosecond laser pulses with argon clusters has been studied by measuring the energy and yield of emitted ions. With two different supersonic nozzles, the dependence of average ion energy (E) over bar on cluster size (n) over bar in a large range of (n) over bar approximate to 3 x 10(3) similar to 3 x 10(6) has been measured. The experimental results indicate that when the cluster size (n) over bar <= 3 x 10(5), the average ion energy (E) over bar proportional to (n) over bar (0.5), Coulomb explosion is the dominant expansion mechanism. Beyond this size, the average ion energy gets saturated gradually, the clusters exhibit a mixed Coulomb-hydrodynamic expansion behavior. We also find that with the increasing gas backing pressure, there is a maximum ion yield, the ion yield decreases as the gas backing pressure is further increased.

飞秒强激光场中大尺寸氩团簇爆炸机理的实验研究

By using time-of-flight spectroscopy, the ionization and explosion of large argon clusters ( (n) over bar = 3 x 10(3) - 3 x 10(6)) in the intense femtosecond pulsed laser field (60 fs,2 x 10(16) W/cm(2)) has been studied, and the dependence of average energy of ions emitted from argon clusters on the gas backing pressure has been measured. By comparing the average ion energies obtained with two different supersonic conical nozzles and considering the Hagena's scaling law of clusters, we have found that the average ion energy is determined by the cluster size when the laser parameters are kept unchanged. The experimental results indicated that when the cluster size is less than 3 x 10(5) atoms per cluster, the Coulomb repulsion force is the dominating factor in the expansion mechanism. Beyond this size, for 3 x 10(5) < (n) over barn < 3 x 10(6), the expansion is the result of the combined effect of both the Coulomb repulsion force and the hydrodynamic force, and the latter will play the dominating role for increasing cluster size.

Coulomb expansion of deuterated methane clusters irradiated by an ultrashort intense laser pulse

The simulations of three-dimensional particle dynamics show that when irradiated by an ultrashort intense laser pulse, the deuterated methane cluster expands and the majority of deuterons overrun the more slowly expanding carbon ions, resulting in the creation of two separated subclusters. The enhanced deuteron kinetic energy and a narrow peak around the energy maximum in the deuteron energy distribution make a considerable contribution to the efficiency of nuclear fusion compared with the case of homonuclear deuterium clusters. With the intense laser irradiation, the nuclear fusion yield increases with the increase of the cluster size, so that deuterated heteronuclear clusters with larger sizes are required to achieve a greater neutron yield.

Influence of vapor transport equilibration on the crystal quality and thermal-expansion coefficients of gamma-LiAlO2

gamma-LiAlO2 (LAO) single crystal has been grown by the Czochralski method. However, its quality was deteriorated due to lithium volatilization during the crystal growth. The full width at half maximum value drops from 116.9 to 44.2 arc sec after the LAO slice was treated by vapor transport equilibration at 1000, 1100, and 1200 degrees C/48 h in sequence. The treated slice shows higher optical transmission than the as-grown one in the measured wavelength range of 190-1900 nm, meanwhile, its absorption edge exhibits a blueshift. According to Raman spectra, the treated slice has homogeneous quality at different depths from surface to 0.01 mm. The expansion coefficient of the treated slice for a axis drops from 17.2398x10(-6)/degrees C to 16.5240x10(-6)/degrees C, and that for c axis drops from 10.7664x10(-6)/degrees C to 10.0786x10(-6)/degrees C.

In situ synthesis of ZrO2/ZrW2O8 composites with near-zero thermal expansion

In this paper, ZrO2 and WO3 were used as the raw materials to prepare ZrO2/ZrW2O8 composites by in situ reaction method and the thermal expansion property of the composites was studied. This novel method included a heating step up to 1473 K for 24 h, which combines the synthesizing and sintering of ZrW2O8. The result indicates that ZrO2/ZrW2O8 composite shows near-zero thermal expansion when the weight ratio of ZrO2 and WO3 is 2.5:1. Compared with composites prepared previously by non-reactive sintering of ZrO2 and ZrW2O8, the composites show higher relative density and lower porosity.

Thermal and electric conductivity of near-zero thermal expansion ZrW 2O8//ZrO2 composites

In this work, the microstructure, thermal and electric conductivity properties of near-zero thermal expansion ZrW2O8/ZrO2 and Al2O3 added ZrW2O8/ZrO2 composites were studied. Both the two composites exhibit very low thermal conductivity and the thermal conductivity decreases slightly as the temperature increases. The electric conductivity of the two composites increases with the increasing of the measurement temperature. The Al2O3 added ZrW2O8/ZrO2 composite has higher thermal and electric conductivity than ZrW2O8/ZrO2 composite. The most important factor which causes the difference of the thermal and electric conductivity of the composites is the porosity. (C) 2008 The Ceramic Society of Japan. All rights reserved.