In this work, we present an investigation of the nonlinear optical properties of nanoshells of different size in solutions
and deposited on glass substrates using a single beam z-scan method at a wavelength of 806 nm with laser duration of
170 fs. Structural properties of gold nanoshells of about 150 and 220 nm, prepared in water, are characterized by AFM
and TEM microscopy. It is found that, in general, they behave as saturable absorbers. The level of saturation depends on
the relative overlap between the plasmon resonance of nanoshells and the laser excitation wavelengths. The nonlinear
absorption coefficient, obtained by fitting the experimental results, is of the order of -10<sup>-11</sup> cmW<sup>-1</sup>.