Degree

Doctor of Philosophy (PhD)

Department

Chemistry

Document Type

Dissertation

Abstract

Laser ablation dynamics encompasses studies of fundamental physical processes of mid infrared laser ablation. Understanding the mechanisms of IR laser desorption and ionization can lead to improvements in laser ablation-based techniques and expansion of their applications. Control of material removal ensures both accuracy and precision of the laser ablation-based techniques. The laser ablation mechanism in the studied wavelength region, is a process of water vaporization and photothermal disruption of tissue. Glycerol was used as the ablation target to establish the methods. Experiments were first aimed at developing methods to monitor material removal during ablation using a 2.94 µm wavelength mid-IR laser at laser fluences between 5 and 50 kJ/m2. This was achieved by using continuous visible laser light scattering in the expanding plume at atmospheric pressure and laser induced acoustic waves. Instantaneous plume velocities for glycerol and rat liver tissue were determined at distances 0.5 – 2.0 mm from the sample surface. The fraction of the laser energy transferred to the expanding shock wave was determined using the Taylor shock wave model. Efficient energy conversion at higher laser fluences is consistent with a phase explosion mechanism. A piezoelectric based method for measuring absorbed laser energy was demonstrated for ablation of glycerol and rat liver tissue. The higher fluence required for tissue compared to glycerol is likely due to its greater tensile strength which necessitates a greater volumetric energy density for particle formation and ejection. Automation of the laser ablation and monitoring system was achieved using a LabVIEW software algorithm. A system was developed for the real-time data acquisition, measure the laser energy absorbed by the sample and adjusting the laser pulse energy to control the material removal.

Date

4-5-2023

Committee Chair

Kermit, Murray K

DOI

10.31390/gradschool_dissertations.6119

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