With the development of high-power laser sources, the study and design of optical limiting systems that protect fine components like eyes and sensors have gained importance. The hazard, due to the narrow divergence of the laser beam and the resulting tightly-focussed spot on the sensor requires a protection in some regions of the spectra, including the visible and infrared domains. This protection could be thought as a material that rapidly interrupts or limits the transmission of the beam to a safe level when reaching very high intensities.

Nanomaterials like nano-oxides should be promising candidates for limiting materials. Recent studies have shown that carbon nanotubes exhibit efficient properties for limiting systems in the near infrared domain. The aim of our study is to develop a protective system in the far infrared domain, using nano-oxides synthesised via sol-gel methods, allowing to obtain advanced and functional powders and coatings of high optical quality. Sol-gel process exhibits the advantages of being an easily modified synthesis of nano-oxides making possible to tune many structural and morphological parameters. Our aim is to correlate the optical response of these nanoparticles at the nanoscale as functions of these various preparation parameters.

Niobium(V) oxide (Nb₂O₅) powders were prepared by the sol-gel procedures from niobium ethoxide, Nb(OC₂H₅)₅.

Non linear optical limiting properties of these oxides were investigated using the Z-scan method which enables to measure both the nonlinear refractive index and absorption coefficient.

Fig. 1 Sample A : Z-scan results and SEM Fig. 2 Sample B : Z-scan results and TEM

These nano-oxide Nb₂O₅ materials show interesting optical non linear properties (fig 1 and 2) depending on the structural, compositional and morphological nanoscale characteristics, which can be finely tuned using different modifications and variations of the Nb₂O₅ sol-gel synthesis.

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