8 March 2014 Application of a laser heterodyne technique to characterize surface acoustic waves generated via a pulsed laser excitation
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Abstract
A CW laser heterodyne spectrometer has been assembled with time resolved data acquisition for probing surface acoustic waves (SAWs) generated by the interaction of a pulsed laser and surface. Literature suggests that SAWs can enhance chemical catalysis, nucleation and surface chemical mobility. Pulsed lasers are known to induce SAWs with bandwidth that is inversely proportional to the pulse width. The goal of this experiment is to apply laser heterodyne spectroscopy to understand the photophysical interactions that promote the formation of laser induced SAWs. The experiment explores the effects produced by a 100 Hz repetition rate UV (355nm) laser with a 6 ns pulse width. Silicon (111) is used as the substrate material, making it is less likely for propagating non linear waves to experience anisotropy. The development of the time-resolved heterodyne spectrometer includes the development of specific data acquisition and software analysis tools to monitor sub-nanometer surface displacements. In addition, to insure that the pulsed laser irradiated material remains within the thermoelastic regime as opposed to ablation, a 2D laser thermal heating model is used to define the duty cycle of the repetitive pulsed laser. Results show that it is possible to measure and analyze laser induced SAWs many centimeters away from the source and substrate dispersion affects the spectral properties of the propagating SAWs. Under controlled conditions, we have measured surface vertical displacements approaching 0.1nm.
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Anthony J. Manzo, Anthony J. Manzo, Henry Helvajian, Henry Helvajian, } "Application of a laser heterodyne technique to characterize surface acoustic waves generated via a pulsed laser excitation", Proc. SPIE 8967, Laser Applications in Microelectronic and Optoelectronic Manufacturing (LAMOM) XIX, 89670N (8 March 2014); doi: 10.1117/12.2041211; https://doi.org/10.1117/12.2041211
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