Metallic Ablation Model

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

2. 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. Linford’s 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. Aspland’s Lab, Benson Bldg) • Measure size of ablation (Optical Microscopy Lab, Clyde Bldg.) • Evaluate Model’s prediction ability

3. Modeling Qsource Qreflect Qabsorb • Assumptions: • Neglect Convection and Conduction (Due to 4ns time frame) • Uniform Gold Properties • Ambient Temp: 296 K Reflectivity's effect On Energy Absorption Energy Absorbed [2]: Ablation rate [1]: 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 Basic Energy Balance Qabsorb=Qsource-Qreflect

4. Modeling • Model predicts required Power (I in Watts) to ablate a desired area A (m2) • 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

5. Results • Measured • Based on ablation area measured with optical microscope • Predicted • Predicted laser energy required to ablate desired area

6. 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

7. Appendix • Welch Ashley J. The thermal Response of Laser Irradiated Tissue. IEEE Journal of Quantum Electronics 1984; QE-20:12:1471- 1481. • 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): 545-552.