Z-scan analysis for photorefractive LiNbO3:Fe crystals of arbitrary thickness

We present an analytical theory for the large-phase-shift, thick Z-scan transmittance, which could be applied to a wide range of medium thickness from the thin sample limit to a thick medium and to small and large nonlinear phase shifts. The theoretical results were experimentally verified for in photorefractive LiNbO3:Fe crystals by using two kinds of closed-aperture Z-scan measurements with a Ti-sapphire laser source (lambda = 810 nm): (1) sample-thickness-dependent Z-scans with thin and thick samples and (2) normalized-thickness-factor-dependent Z-scans with different external lenses having different focal lengths in the same thick LiNbO3:Fe crystal.