Metallic Ablation ModelME 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. 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

Modeling• Assumptions:

• Neglect Convection and Conduction (Due to 4ns time frame)• Uniform Gold Properties• Ambient Temp: 296 K

)( LTc

I

t

z

Qabsorb

Qsource

Qreflect

Basic Energy BalanceQabsorb=Qsource-Qreflect

zabsorbed eIRQ )1(

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 effectOn Energy Absorption

Modeling

zeR

ALcTtz

AI

)1(

)()(

• 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

Results• Measured

• Based on ablation area

measured with optical

microscope

• Predicted • Predicted laser energy

required to ablate desired

area

QMeasured 2210 W

QPredicted 4725 W

Percent Error 53.2 %

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-20:12:1471-1481.

2. 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.