The energy density of laser cutting machine

Laser cutting machine energy density is a very important parameter, it is decided to film thickness and composition of one of the key factors. In selected under the condition of the target material and laser wavelength, laser energy density on the surface of the target material to the influence of the ablative material particle size and density of the most significant. According to the principle of pulse laser sputtering deposition film, laser cutting machine energy density must be above a certain threshold Et to make the material corrosion, evaporation, since the role of the pulse laser and target essentially different from thermal evaporation process, its energy density must make target surface plasma, thereby Knudsen in target surface complex layered structure layer, can ensure that target membrane composition. On the premise of constant laser power, particle number density is usually with the reduce of spot size increases. In general. Sui condition there exists a threshold laser energy density Et, almost no particles under its surface. In terms of YBCO high temperature superconductor materials, for example, when using pulse width is 20 ns XeCl excimer laser, Et is 0.9 J/cm2 on Et, grain density increased with the increase of the energy density has increased dramatically. If further increase the energy density, particle number density increase rate began to decline, and tends to saturation.
With the improvement of energy density of laser cutting machine, the film growth rate will increase. When pulse energy increase, the target material surface absorbs more energy, stripping, the plasma density, arrived in the density of atoms on the surface of the substrate and the substrate surface to absorb the atomic frequency increases, lead to the nucleation rate increases, thus improve the speed the growth of thin films. If the energy density of laser cutting machine is too high, will bring the negative impact of the two aspects: one is plasma of high speed, intensifying high-energy particle collisions with substrate, the inverse particles is too strong, so easily formed in the substrate surface vacancy defects; 2 it is can make the target temperature, temperature difference, surface blasting power increases, lead to the target surface micro explosion, the explosion of larger particles composition proportion increase, the evaporation part ratio decreases, and the resulting liquid particles also can reduce film quality. Therefore, in the pulse laser sputtering deposition film, select the appropriate laser energy density is very important, and the best range of energy density of laser cutting machine owing to the different target material.

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