Carlos G. Treviño-Palacios

Spatial nonreciprocity in waveguide second-order processes

We show numerically and experimentally that second-harmonic generation in spatially nonsymmetrical structures can show a direction-dependent or nonreciprocal behavior under a variety of conditions.

Review of the nonlinear common path interferometer

The nonlinear common path interferometer is a simple and robust single lens optical processor using an intensity dependent medium placed on its geometrical focal plane to observe deformed wavefronts. It is described either as a nonlinear inteferometer or as an image processor. We demonstrate that this system requires excess surrounding illumination beyond the geometrical boundaries of the disturbance to operate. We discuss recent progress on this setup. In particular, the effect of large phase changes in the filter and the dynamics of the filter formation.

Flow visualization using nonlinear phase contrast

In this work, we show a simple single lens system using laser light illumination to observe flow dynamics. It is based on a phase contrast technique in which the filter is made of a nonlinear optical material, therefore it is self-aligned and depends mainly on the illuminating intensity. Due to these characteristics, the resulting setup is extremely robust and builds up within a few milliseconds.

Photo-EMF effect in polydiacetylene PTS

In this work we report for the first time observation of AC photocurrents generated by photo-emf effect in high quality crystals of the conjugated polymer 2,4-hexadiyne-1,6-diol-bis-(para-toluene sulfonate) or polydiacetylene PTS (usually referred simply as PTS). We used illumination at λ=633nm where the absorption spectra has its peak. In principle, photocurrent at this wavelength should be small due to the large exciton binding energy, however we show that relative large photocurrents can be observed at modest electric fields (up 2000 V/cm). When the sample is illuminated with a periodically oscillating interference pattern it leads to spatial redistribution of charge carriers among traps. Spatial overlap of the resulting space-charge field with the oscillating photoconductivity pattern gives rise to an oscillating photocurrent (photo-emf signal). From photo-emf measurements, a Maxwell relaxation time of 0.17 sec at 6 W/cm2 and lifetime of carriers of 6 ms were estimated. The later was confirmed from photoconductivity measurements.

Polydiacetylene PTS: A Molecular Quantum Wire with Exceptional Optical Properties

The conjugated polymer 2,4-hexadiyne-1,6-diol-bis-(para-toluenesuIfonate) or PTS is a classical example of a one-dimensional quantum wire. The π-electrons can move more or less freely in one dimension. There are large repercussions to this effect in the photonics field, including photoconductivity, and the linear and nonlinear optical response. Growing techniques of crystals with high optical quality as well as measurements on a variety of nonlinear optical effects of PTS are reported in this chapter. These include measurements on the large magnitude of the exciton absorption line, the well-defined vibrational side bands at room temperature, massive two and four photon absorption coefficients, very large Raman gain coefficients, minimal excited state absorption and a large nonlinear refractive index.

Spatial chirping of wavevector mismatch in LiNbO/sub 3/ segmented waveguides for engineering of specific second-harmonic generation detuning curves for cascading applications

A new aspect of second-order nonlinearities, namely the generation of large nonlinear phase shifts from cascading, has prompted a great deal of interest. To date high throughput all optical switching using cascaded second-order nonlinearities has been experimentally demonstrated in temperature-tuned waveguide second-harmonic generation (SHG). The success of these devices is based on the spatial nonuniform wavevector distribution and the unique nonlinear phase shift introduced by the temperature tuning method used for phase matching. With the development of quasi-phase-matching (QPM) techniques it is now possible to achieve the required, flexible, grating-assisted phase matching at almost any wavelength by spatial control of the grating period.