Optical susceptibilities of supported indium tin oxide thin films.

The third-order nonlinear optical susceptibility of indium tin oxide (ITO) thin films on glass substrates, χ(3)ITO, was determined in the near-IR spectral region using degenerate four wave mixing (DFWM) spectroscopy with 100 fs laser pulses. A DFWM method for measuring thin films on thick substrates was refined for the characterization of films less than 100 nm thick and applied to ∼25 nm thick ITO films. It was found that χ(3)ITO is purely electronic at 900–1300 nm (11 000–7700 cm-1) and has a value of (2.16±0.18)×10-18 m2 V-2. The χ(3)ITO value reaches (3.36±0.28)×10-18 m2 V-2 at 1500 nm (6700 cm-1) due to two-photon absorption by free carriers (electrons). Ultrafast electron relaxation was also observed. The ∼100 fs lifetime of this process could reflect electron scattering in the conduction band. [ABSTRACT FROM AUTHOR]