Femtosecond Z-scan measurement of GaN

Nonlinear refractive index n(2) of GaN was measured for the below-band-gap ultraviolet (UV) wavelength region using Z-scan techniques with femtosecond UV pulses. A large nonlinear refractive index of -2.9 +/- 1.2x 10(-12) cm( 2)/W was obtained at a wavelength of 368 nm. The distribution of n(2) versu s wavelength was found to be consistent with a model described by the quadr atic Stark effect, which is the dominant factor contributed to the nonlinea r refractive index near the band gap. Our experiments show that GaN is an e xcellent nonlinear material with large negative n(2) in the UV region. (C) 1999 American Institute of Physics. [S0003-6951(99)01948-8].