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We present a simple yet highly sensitive single-beam experimental technique for the determination of both the sign and magnitude of n(2). The sample is moved along the z direction of a focused Gaussian beam while the repetitively pulsed laser energy is held fixed. The resultant plot of transmittance through an aperture in the far field yields a dispersion-shaped curve from which n(2) is easily calculated. A transmittance change of 1% corresponds to a phase distortion of approximately lambda/250. We demonstrate this method on several materials using both CO(2) and Nd:YAG laser pulses.

We present novel results obtained in the fabrication of high-aspect ratio micro-fluidic microstructures chemically etched from fused silica substrates locally exposed to femtosecond laser radiation. A volume sampling method to generate three-dimensional patterns is proposed and a systematic SEM-based analysis of the microstructure is presented. The results obtained gives new insights toward a better understanding of the femtosecond laser interaction with fused silica glass (a-SiO(2)).

We extend the application of the Z-scan experimental technique to determine free-carrier nonlinearities in the presence of bound electronic refraction and two-photon absorption. We employ this method, using picosecond pulses in CdTe, GaAs, and ZnTe at 1.06 m and in ZnSe at 1.06 and 0.53 Am, to measure the refractive-index change induced by two-photon-excited free carriers (coefficient ar,), the two-photon absorption coefficient 1, and the bound electronic nonlinear refractive index n 2. The real and imaginary parts of the third-order susceptibility (i.e., n 2 and 13, respectively) are determined by Z scans with low inputs, and the refraction from carriers generated by two-photon absorption (an effecitve fifth-order nonlinearity) is determined from Z scans with higher input energies. We compare our experimental results with theoretical models and deduce that the three measured parameters are well predicted by simple two-band models. n 2 changes from positive to negative as the photon energy approaches the band edge, in accordance with a recent theory of the dispersion of n 2 in solids based on Kramers-Kronig transformations [

The bound electronic nonlinear refractive index, n 2 • and two-photon absorption (2PA) coefficient, 6, are measured in a variety of inorganic dielectric solids at the four harmonics of the Nd:YAG laser using Z scan. The specific materials studied are: barium fluoride (BaF 2), calcite (CaC0 3), potassium bromide (KBr), lithium fluoride (LiF), magnesium fluoride (MgFz), sapphire (Ab03), a tellurite glass (75%Te0z+ 20%Zn0 + 5%Na 2 0) and fused silica (SiOz), We also report n 2 and 3 in three second-order, x(z), nonlinear crystals: potassium titanyl phosphate (KTiOP04 or KTP), lithium niobate (LiNb0 3), and /)-barium borate (8-BaBz0 4 or BBO). Nonlinear absorption or refraction can alter the wavelength conversion efficiency in these materials. The results of this study are compared to a simple twoparabolic band model originally developed to describe zincblende semiconductors. This model gives the bandgap energy (E 9) scaling and spectrum of the change in absorption. The dispersion of nz as obtained from a Kramers-Kronig transformation of this absorption change scales as E-,; 4 • The agreement of this theory to data for semiconductors was excellent. However, as could be expected, the agreement for these wide bandgap materials is not as good, although general trends such as increasing nonlinearity with decreasing bandgap energy can be seen. I. INTRODUCTION T HE DISPERSION of the nonlinear refraction (NLR) and spectrum of nonlinear absorption (NLA) are measured in the following samples: barium fluoride (BaF 2), calcite (CaC0 3), potassium bromide (KBr), lithium fluoride (LiF), magnesium fluoride (MgF 2), sapphire (Ab0 3), a tellurite glass (75%Te0 2 + 20%Zn0+ 5%Na 2 0) and fused silica (Si0 2). 1 Measurements are made at the four harmonics of a TEM 00 , single-pulse, picosecond Nd:YAG laser (i.e., A = Manuscript