New and very stable polymers with good optical third-order nonlinearities have been prepared by condensation between a copolymer of maleic anhydride and octadecene and appropriate Disperse Red and Disperse Orange type chromophores. The nonlinear response of low concentration solutions of the polymers has been determined using a new numerical Z-scan technique. The polymers have been found highly stable, and their nonlinear response is very reproducible, both under intense illumination and upon several repeated experiments over months. Especially the polymer where the Disperse Orange 3 chromophore is incorporated in the main chain through imide linkages displays both the highest refractive nonlinearity and almost no two-photon absorption. Its surprisingly higher nonlinear response with respect to the parent Disperse Orange 3 is demonstrated and discussed.

This paper demonstrates the use of a nonlinear upconversion process to observe an infrared source through a telescope array detecting the interferometric signal in the visible domain. We experimentally demonstrate the possibility to retrieve information on the phase of the object spectrum of an infrared source by using a three-arm upconversion interferometer. We focus our study on the acquisition of phase information of the complex visibility by means of the phase closure technique. In our experimental demonstration, a laboratory binary star with an adjustable photometric ratio is used as a test source. A real time comparison between a standard three-arm interferometer and our new concept using upconversion by sum-frequency generation demonstrates the preservation of phase information which is essential for image reconstruction.

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In the field of high resolution imaging in astronomy, we experimentally demonstrate the spatial-coherence analysis of a blackbody using an up-conversion interferometer in the photon counting regime. The infrared radiation of the blackbody is converted to a visible one in both arms of the interferometer thanks to the sum-frequency generation processes achieved in Ti-diffused periodically poled lithium niobate waveguides. The coherence analysis is performed through a dedicated imaging stage which mimics a classical telescope array analyzing an astrophysical source. The validity of these measurements is confirmed by the comparison with spatial-coherence analysis through a reference interferometer working at infrared wavelengths.