Shadowgraphic imaging of carbon nanotube suspensions in water and in chloroform

Carbon nanotube suspensions are known to display interesting optical limiting properties as a result of the formation of solvent or carbon-vapor bubbles that scatter the laser beam. In this study we present an original experiment that permits direct observation of the changes that occur in the focal zone in carbon nanotube suspensions by using a shadowgraphic experiment coupled with a monochromatic pump-probe experiment. We have observed a clear correlation between the radius of the scattering centers and the evolution in transmittance of the sample. We compared bubble growth in chloroform and water and found good agreement with previously obtained results. We also observed the presence of compression waves, which propagate parallel to the laser beam and can produce secondary cavitation phenomena after reflection on the cell walls.