Experimental example of isotropic surface second-harmonic generation: dc-sputtered air-exposed aluminum thin films

Abstract

We have determined the amplitudes and relative phases of the allowed components of the effective surface second-harmonic susceptibility, Χ ( 2 ) , for a set of air-exposed dc-sputtered Al thin films. The second-harmonic intensity and polarization state was measured as a function of linear input polarization state and azimuthal orientation of the sample using a Ti:sapphire laser at 810 nm. The films are found to be optically isotropic with respect to azimuthal rotation angle, consistent with an isotropic Χ ( 2 ) with seven elements in three families. Using measured linear optical properties, the elements of Χ ( 2 ) were determined from the data. In terms of the dimensionless parameters a, b, and d [J. Rudnick and E. A. Stern, Phys. Rev. B 4, 4274 (1971)], we find ‖a‖=2.30′0.72, in rough agreement with previous measurements of the surface current perpendicular to the surface on oxidized Al surface, ‖b‖=0.013′0.004 for the surface current parallel to the surface, and ‖d‖ =0.009′0.002 for the bulk contribution. The relative phases of a and b with respect to d are found to be (-0.4′6)° and (63′12)°, respectively. The measurement indicates a large discrepancy between measured values and the universal theoretical expectation that b=-1 and d= 1.