Metallic Ablation Model ME 340: David Matsumura/Ryan Sydenham Funding provided by Millennial Data, Inc. 3D model pictured above compliments of Dr. Vladimir Solovjov

Project Summary Objective Determine energy necessary to ablate volumetric regions of thin gold film on transparent polymer substrate Develop a model to relate ablation region to emitted laser power To secure further funding, model was required to predict, on the same order of magnitude as experimental value would suggest, the required ablation energy Procedure Prepare substrate by cleaning with detergent, rinsing in deionized water, and then rinsing with ethanol (Dr. Linfords lab, Benson Bldg) Deposit 100 nm Au thin film by means of Electron Beam Deposition (BYU Cleanroom, 10PPM) Ablate gold with 532 nm Laser, set to energy level determined by model (Dr. Asplands Lab, Benson Bldg) Measure size of ablation (Optical Microscopy Lab, Clyde Bldg.) Evaluate Models prediction ability

Modeling Assumptions: Neglect Convection and Conduction (Due to 4ns time frame) Uniform Gold Properties Ambient Temp: 296 K Q absorb Q source Q reflect Basic Energy Balance Q absorb =Q source -Q reflect Ablation rate [1]: Energy Absorbed [2]: Where dz=ablation depth, dt=laser pulse duration, ρ=Au density, c=heat capacity of Au, ΔT=temperature change required to vaporize Au, L=heat of vaporization of Au, R=reflectivity of Au, I=laser pulse power, α=absorption coefficient Reflectivity's effect On Energy Absorption

Modeling Model predicts required Power (I in Watts) to ablate a desired area A (m 2 ) Based on aforementioned models Where dz=ablation depth, dt=laser pulse duration, ρ=Au density, c=heat capacity of Au, ΔT=temperature change required to vaporize Au, L=heat of vaporization of Au, R=reflectivity of Au, I=laser pulse energy, α=absorption coefficient, A=desired ablation area

Results Measured Based on ablation area measured with optical microscope Predicted Predicted laser energy required to ablate desired area Q Measured 2210 W Q Predicted 4725 W Percent Error53.2 %

Conclusion & Recommendations Objective Achieved Predicted value was on the same order of magnitude as the measured value In general, heat transfer models will only be accurate within ±20% Discrepancies Laser power value emitted from laser based on no energy loss In actuality, there are significant energy loses as laser energy is filtered down to desire value and directed/focus to destination If laser energy experienced by au film is actually half of what is was intended to be the margin of error decreases to 6% (this is very likely) Some heat conduction or convection may actually exist, probably still should be neglected Model, applied to another test, helped to secure further funding Reliable method of determining laser output power needs to be determined and then model should be retested

Appendix 1.Welch Ashley J. The thermal Response of Laser Irradiated Tissue. IEEE Journal of Quantum Electronics 1984; QE-20:12: Zhang, X., S. S. Chu, J. R. Ho, and C. P. Grigoropoulos. "Excimer Laser Ablation of Thin Gold Films on a Quartz Crystal." Applied Physics a: Materials Science & Processing 64 (1997):