PHYSICAL REVIEW A 73, 053812 (2006)

Ultrafast third-harmonic generation from textured aluminum nitride–sapphire interfaces

D. S. Stoker,^1,2,* J. Baek,^3,2 W. Wang,^3,2,† D. Kovar,^4,2 M. F. Becker,^3,2 and
J. W. Keto^5,2
1Department of Physics, The University of Texas at Austin, 1 University Station C1600, Austin, Texas 78712-0264, USA
²Center for Nano- and Molecular Science and Technology and the Texas Materials Institute, The University of Texas at Austin,
Building ETC, Room 8.102, Campus Mail Code C2201, Austin, Texas 78712-1063, USA
³Electrical and Computer Engineering, The University of Texas at Austin, 1 University Station C0803, Austin, Texas 78712-0240, USA
⁴Mechanical Engineering Department, The University of Texas at Austin, 1 University Station C2200, Austin,
Texas 78712-0292, USA
⁵Department of Physics, The University of Texas at Austin, 1 University Station C1600, Austin, Texas 78712-0264, USA

Received 8 December 2005; revised manuscript received 11 March 2006; published 11 May 2006

We measured and modeled third-harmonic generation THG from an AlN thin film on sapphire using a
time-domain approach appropriate for ultrafast lasers. Second-harmonic measurements indicated that polycrystalline
AlN contains long-range crystal texture. An interface model for third-harmonic generation enabled an
analytical representation of scanning THG z-scan experiments. Using it and accounting for Fresnel reflections,
we measured the AlN–sapphire susceptibility ratio and estimated the susceptibility for aluminum nitride,
χ⁽³⁾_χχχχ (3ω; ω, ω, ω)=1.52±0.25x10⁻¹³ esu. The third-harmonic TH spectrum strongly depended on the laser
focus position and sample thickness. The amplitude and phase of the frequency-domain interference were fit to
the Fourier transform of the calculated time-domain field to improve the accuracy of several experimental
parameters. We verified that the model works well for explaining TH signal amplitudes and spectral phase.
Some anomalous features in the TH spectrum were observed, which we attributed to nonparaxial effects.

DOI: 10.1103/PhysRevA.73.053812 PACS number(s) : 42.65.Ky, 42.65.Re, 78.20. e, 78.47. p