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, chi((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 similar to 25 nm thick ITO films. It was found that chi((3))(ITO) is purely electronic at 900-1300 nm (11 000-7700 cm(-1)) and has a value of (2.16 +/- 0.18)x10(-18) m(2) V-2. The chi((3))(ITO) value reaches (3.36 +/- 0.28)x10(-18) m(2) V-2 at 1500 nm (6700 cm(-1)) due to two-photon absorption by free carriers (electrons). Ultrafast electron relaxation was also observed. The similar to 100 fs lifetime of this process could reflect electron scattering in the conduction band. (c) 2006 American Institute of Physics.