03/28/2023
By Zibo Wang

All are invited to the doctoral dissertation defense by Zibo Wang on "The nonlinear optical properties of gold nanostructures excited by a femtosecond laser pulse above the damage threshold."

Candidate name:​ Zibo Wang​
Date:​ Monday, April 10, 2023
​Time: 5 to 7 p.m. EDT
Location:​ Olney 136D (Conference Room). ​If you are interested in attending remotely, please contact the student (Zibo_Wang@student.uml.edu) to obtain the Zoom link.
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Committee:

  • Chair/Advisor Mengyan Shen, Professor, Department of Physics and Applied Physics, University of Massachusetts Lowell​
  • Jayant Kumar, Professor, Department of Physics and Applied Physics, University of Massachusetts Lowell​
  • Cecil Joseph, Assistant Teaching Professor, Department of Physics and Applied Physics, University of Massachusetts Lowell​

Abstract:​

The optical properties of gold nanostructures were examined using destructive laser pulses. Femtosecond laser pulses with fluences up to 10^6 J/m2 were applied to gold nanorods and 100-nm gold films, both of which had a higher damage threshold than the fluence used. A spectral hole-burning experiment was carried out on the gold nanorods, while the complex refractive index of the gold film was calculated using its reflectivity and transmissivity. The real part of the complex refractive index displayed a peak at around 10 kJ/m2, which is near the damage threshold. The complex third-order nonlinear susceptibility χ3 was determined to be (7.43-2.25i)×10^(-21) m^2/V^2, which supports previous research indicating that it decreases as pulse duration decreases. A plasmon-photon exchange (PPE) model was further developed to study this nonlinear process. The simulation using the PPE model matched the experimental transmissivity above the damage threshold and explained the increase in the damping factor from the spectral hole burning experiment. The model suggested that the interaction time between photons and plasmons is roughly 500 fs. This model is crucial for comprehending nonlinear optical processes under both extremely high and conventionally low laser irradiations.