Investigation On Vaporization And Plasma Shielding In The Ablation Process Of PLD

Pulsed laser deposition is one of the most attractive new techniques, developed in the 1980's. Then, along with the multi-component oxide high-temperature superconductor discovered, PLD technique makes a great success in depositing such film materials. The PLD technique has so many advantages, such as high pulsed laser energy density, similarity between target and prepared thin film components, the high deposition rate, and lower substrate temperature. In the past two decade years, varieties of functional thin films have been deposited by PLD technique. Now, the development trend of PLD is the ultra short and ultra high laser (ps and fs).At the same time, the development of the relevant physics mechanism research of the PLD technique has flourished. Our group has a general, thorough study in PLD. The paper aims in the ablation process of PLD.The first chapter introduces the PLD technique, including the experiment techniques and the development trend. The second chapter summarizes the systemic and integrated models of the PLD mechanism at present, including the Zhang-Li model, the Zhang-Guan model, and LSAW model. And the flowing chapters involve the fruits of the author on the plasma shielding in ablation process, which contains the vaporization.The contents studied as follows:1)A new theoretical model of pulsed laser ablation has been developed, which studies the characteristics of laser-plasma interaction and the effect of plasma shielding in the ablation process. Two different absorption processes are considered, namely inverse bremsstrahlung and photoionization of excited species, also plasma radiation is included. The model is used to simulate 25 ns square pulsed laser irradiation on YBa₂Cu₃O₇ targets. The evolution of plasma length and transmitted intensity are performed, and the variation of ablation depth per pulse with energy density at three most common excimer wavelengths (193, 248 and 308 nm) are simulated too. Moreover, we obtain the dependence of ablation depth on the number of laser pulses at 248 nm. Under the same experimental conditions, our numerical results are more in agreement with the experimental results, which confirms that plasma shielding plays a relevant role in the ablation process.2 ) The vaporization effect and the following plasma shielding generated by high-power nanosecond pulsed laser ablation are studied in detail based on the heat flux equation. As an example of Si target, we obtain the time evolution of calculated surface temperature, ablation rate and ablation depth by solving the heat flow equations using a finite difference method. It can be seen that plasma shielding plays a more role in the ablation with time. At the same time, we simulate the pulsed laser irradiation Ni target, the evolution of transmitted intensity and variation of ablation depth per pulse with energy density are performed. Our numerical results are more agreed with the experiment datum. The result shows that the plasma shielding is very important.