J. Reif

Femtosecond index grating in barium flouride: efficient self-diffraction and enhancement of surface SHG

A transient refractive index grating is formed in barium fluoride crystals under irradiation with femtosecond laser pulses from two non-collinear beams. At low intensities energy coupling takes place. At high intensities, a typical self-diffraction pattern is obtained with a diffraction efficiency better than 10%. Simultaneously, an enhancement of the SHG signal from the surface, as well as the generation and diffraction of the third harmonic is observable. For all effects the nonlinear Kerr-effect is responsible, with the response time being limited only by the temporal pulse shape.

Efficient instantaneous optical switching and frequency conversion on a femtosecond time scale

In this paper, new results about a transient femtosecond index grating in barium fluoride has been presented. There is a strong indication that the lifetime of the grating is only limited by the pulse width of the laser. Additionally, it is shown how the transient grating promotes highly efficient third-harmonic generation and diffraction due to a self phase matching mechanism. The immediate build-up and decay opens the way to an application as a femtosecond switching device.

Hafnium Oxide on Silicon: A Non-Destructive Characterization of the Interfacial Layer

Quality and stability of the substrate/dielectric interface r challenges for the implementation of new highk gate dielectrics into silicon technology. For our studies, we inve stigated nanometer thin hafnium oxide layers grown on Si substrates by Hf-Si -O-N MOCVD. Subsequent N2 annealing provides a high concentration of nitrogen close to the interf ace, as confirmed by AES, XRR and XPS measurements, indicating a silicon-nitrogen rich interm ediate layer. Samples annealed at low N 2 pressure (with an amorphous hafnium oxide layer, according to XRD mea surements) are compared to samples annealed at high N 2 pressure (with a crystalline HfSiO 4 layer). Micro-Raman measurements reveal that the silicon substrate is under compres sive stress, with similar intensity for both samples. In contrast, band-edge photoluminescence and defect luminescence exhibit pronounced differences: The sample with the crystalline HfSiO 4 phase shows a significantly higher band-edge luminescence than the sample with an amorphous layer. A higher defect luminescence occurred for the sample with the crystalline layer. We c onclude, that the photoluminescence results are strongly related to non-radiative interfacial rec ombinations. Interface-sensitive SHG investigations clearly show the four-fold symmetry of the substrate, indicatin g n intact interface.

Femtosecond nonlinear optical characterisation of silicon wafers: the role of symmetry

Abstract Femtosecond second-harmonic generation from the surface of as-grown 6xa0in silicon wafers is used as a tool for in situ characterisation of Czochralski-grown crystals. Exploiting the symmetry sensitivity of surface SHG, we used a particular two-pulse arrangement, similar to a conventional pump-probe set-up, to obtain non-destructive, in situ information about the location of three commonly known different areas of crystal quality: a central zone of vacancy-rich and an outer zone of interstitial-rich crystal which are separated by a ring of stacking faults. Finally, the applicability of the technique for on-line analysis and control during the growth of different types of gate dielectrics is discussed.

Ultrafast transient grating in barium fluoride: efficient instantaneous optical switching and frequency conversion on a femtosecond time scale

Interference between 100-fs laser pulses generates an instantaneous transient index grating in Barium Fluoride. This travelling thin grating supports strong third harmonic generation and leads to efficient diffraction of the fundamental and the harmonic beams.