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Optical Engineering

Third harmonic microscopy of intrinsic and induced material anisotropy in dielectric thin films
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Paper Abstract

Third harmonic (TH) microscopy with circularly polarized illumination directly reveals material anisotropy owing to suppression of background optical signals from isotropic media. Because optical thin films and their substrates are expected to be highly isotropic, TH microscopy presents a path to study induced and intrinsic anisotropy in films, providing both insight into laser-induced material modification that precedes damage and feedback about the deposition process. Because nanoscale defects and material strain influence the damage behavior of films, we examined TH sensitivity to similar sources of contrast. We demonstrate imaging of individual 10 nm colloidal gold nanoparticles and 100 mN nanoindentations in fused silica both with signal-to-noise ratio (SNR) ≥ 100∶1. We present TH images (SNR ≥ 210∶1) of sites exposed to femtosecond laser pulses below damage in 100 nm HfO2 films that are barely visible (SNR ≤ 2.3∶1) with Nomarski and polarization imaging, traditional microscopic techniques known to display contrast for material anisotropy. At our detection limit (320 mW, 50 fs, 790 nm, ≈ 106 photomultiplier tube gain), we examined root mean square in the TH image of nascent films that correlated to the film's macrostrain. TH microscopy presents a relatively simple all-optical method to monitor nanoscale anisotropy in thin films during exposure to high-intensity radiation and during deposition.

Paper Details

Date Published: 9 July 2012
PDF: 6 pages
Opt. Eng. 51(12) 121807 doi: 10.1117/1.OE.51.12.121807
Published in: Optical Engineering Volume 51, Issue 12
Show Author Affiliations
Reed A. Weber, The Univ. of New Mexico (United States)
Cristina Rodriguez, The Univ. of New Mexico (United States)
Duy N. Nguyen, The Univ. of New Mexico (United States)
Luke A. Emmert, The Univ. of New Mexico (United States)
Wolfgang Rudolph, The Univ. of New Mexico (United States)
Dinesh Patel, Colorado State Univ. (United States)
Carmen S. Menoni, Colorado State Univ. (United States)

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