AVS 53rd International Symposium
    Thin Film Thursday Sessions
       Session TF2-ThA

Invited Paper TF2-ThA3
Dynamics of Ultrafast Laser Generated Ablation from Metals and Semiconductors Close to the Ablation Threshold

Thursday, November 16, 2006, 2:40 pm, Room 2022

Session: Pulsed Laser Deposition of Thin Films
Presenter: S.M. Yalisove, University of Michigan
Authors: S.M. Yalisove, University of Michigan
J.P. McDonald, University of Michigan
Correspondent: Click to Email
The evolution of ultrafast laser generated material ejection close to the ablation threshold can studied with a variety of methods. Ultrafast microscopy has been used to study the expulsion of a thin (~40nm) layer of molten material from metals and semiconductors when irradiated with laser pulses of duration less than ~600 femtoseconds and intensity close to the ablation threshold. These methods use pump-probe techniques to construct a series of time resolved images with resolution limited by the duration of the ultrafast laser pulse. We will present results from Si surfaces with a variety of thermal oxide thicknesses that are irradiated with 780 nm laser pulses of duration 150 femtoseconds at normal incidence. The intensities we have studied range from 1-20 times the ablation threshold. Intensities below 10 times of the ablation threshold generally do not produce optically emitting plasmas. We will show that ablation in this regime is fundamentally different that at higher intensities. Three different pump-probe imaging methods will be presented; Newton's ring analysis at normal incidence, side view imaging at grazing incidence, and a new method using a delayed pulse to excite optical emission of the ejected material. While many physical processes occur on the sub picosecond time scale, ejection of material typically occurs about 1-10 picoseconds after ultrafast laser irradiation. The images in this study are acquired every 50 picoseconds up to about 12 nanoseconds after irradiation. Movies made from these images will be shown. Analysis of the results from these studies will be presented including momentum transfer and efficiency of these processes, a physical model to explain phenomena observed with varying oxide thickness and laser fluence, and the different dimensionalities of Sedov-Taylor scaling that are observed. The impact of these studies on ultrafast pulsed laser deposition will be discussed.