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Study of laser ablation plasma using time resolved imaging and modeling
Author
Shahid Mahmood
Supervisor
Lee, Paul Choon Keat
Rawat, Rajdeep Singh
Abstract
Laser ablation is used in fundamental research and industry for micromachining, lithographic patterning, cleaning of surfaces, surgery and synthesis of novel materials. The removal of material from a thin surface layer using a laser is called laser ablation. The processes of ablation and expansion are controlled by the set parameters such as (i) characteristics of laser pulse (wavelength, pulse width, energy fluence etc), (ii) characteristics of ambient gas (gas type, gas pressure etc.) and (iii) characteristics of target materials. Research work done by many researchers on pulsed laser ablation in pulsed laser deposition (PLD) systems has shown that these parameters strongly influence the plasma plume dynamics.
Although the deposition of thin films or nano-structured materials using the PLD is a simple technique in terms of the experimental setup, the expansion dynamics of ablated plume from the target surface to the substrate is a complex process. This research project focuses on investigating the relationship between the laser ablation and expansion parameters and plume dynamics which may lead to a better understanding of the link between the properties of the deposited thin film and the ablation and expansion processes.
The laser ablated plasma expansion can be predicted using several available empirical and fundamental models. The models used in the present work are (i) snow plow and (ii) shock wave. The snow plow model and shock wave models are based on the conservation laws of physics, in addition the shock wave model also uses the equations of state. The snow plow and shock wave models estimate most of the plasma ablation and expansion parameters.
The ablation was done using a pulsed laser at different wavelengths and energies. Time resolved images of the expansion of plumes of Fe, Al, Si, and graphite targets at various pressure of Ar, N2, and Ne gases were recorded. The raw data obtained from the imaging was used to see the expansion trends of different plumes by plotting their front edge position versus time. Simultaneously the simulation of plasma expansion was done using the various fundamental and empirical models. The data from the simulation were fitted to the experimental values. The results obtained from the comparison of experimental and calculated data were analysed and used to explain the effect of the parameters on the plume dynamics during its transition from the target surface up to the substrate. By comparing experimental findings and simulation data we were able to estimate the laser energy absorbed, average mass ablated per laser shot and the ambient gas density. In addition to the estimation of experimental and ablation parameters by fitting of the imaging results using snow plow and shock model, a detailed investigation of interesting plume features such as plasma plume splitting (simultaneous strong emission from two different zones of plasma plume) and the Rayleigh-Taylor (RT) instabilities at the plume front have been done and reported. The results from this research work could be helpful for the researchers working on PLD systems as we investigated how the background gas pressure, laser energy fluence and laser wavelength may lead to the change in the topography of the deposited thin films which could be due to the change in the size of the nanoparticles, nanoparticle agglomerations and amount of ablated material.
Although the deposition of thin films or nano-structured materials using the PLD is a simple technique in terms of the experimental setup, the expansion dynamics of ablated plume from the target surface to the substrate is a complex process. This research project focuses on investigating the relationship between the laser ablation and expansion parameters and plume dynamics which may lead to a better understanding of the link between the properties of the deposited thin film and the ablation and expansion processes.
The laser ablated plasma expansion can be predicted using several available empirical and fundamental models. The models used in the present work are (i) snow plow and (ii) shock wave. The snow plow model and shock wave models are based on the conservation laws of physics, in addition the shock wave model also uses the equations of state. The snow plow and shock wave models estimate most of the plasma ablation and expansion parameters.
The ablation was done using a pulsed laser at different wavelengths and energies. Time resolved images of the expansion of plumes of Fe, Al, Si, and graphite targets at various pressure of Ar, N2, and Ne gases were recorded. The raw data obtained from the imaging was used to see the expansion trends of different plumes by plotting their front edge position versus time. Simultaneously the simulation of plasma expansion was done using the various fundamental and empirical models. The data from the simulation were fitted to the experimental values. The results obtained from the comparison of experimental and calculated data were analysed and used to explain the effect of the parameters on the plume dynamics during its transition from the target surface up to the substrate. By comparing experimental findings and simulation data we were able to estimate the laser energy absorbed, average mass ablated per laser shot and the ambient gas density. In addition to the estimation of experimental and ablation parameters by fitting of the imaging results using snow plow and shock model, a detailed investigation of interesting plume features such as plasma plume splitting (simultaneous strong emission from two different zones of plasma plume) and the Rayleigh-Taylor (RT) instabilities at the plume front have been done and reported. The results from this research work could be helpful for the researchers working on PLD systems as we investigated how the background gas pressure, laser energy fluence and laser wavelength may lead to the change in the topography of the deposited thin films which could be due to the change in the size of the nanoparticles, nanoparticle agglomerations and amount of ablated material.
Date Issued
2010
Call Number
QC718.5.L3 Sha
Date Submitted
2010