Abstract
Nowadays, the use of lasers has become commonplace in everyday life, and laser protection has become an important field of scientific investigation, as well as a security issue. In this context, optical limiters are receiving increasing attention. This work focuses on the identification of the significant parameters affecting optical limiting properties of aqueous suspensions of pristine single-wall carbon nanohorns. The study is carried out on the spectral range, spanning from ultraviolet to near-infrared (355, 532 and 1064 nm). Optical nonlinear properties are systematically investigated as a function of nanohorn morphology, concentration, dimensions of aggregates, sample preparation procedure, nanostructure oxidation and the presence and concentration of surfactants to identify the role of each parameter in the nonlinear optical behavior of colloids. The size and morphology of individual nanoparticles were identified to primarily determine optical limiting. A cluster size effect was also demonstrated, showing more effective optical limiting in larger aggregates. Most importantly, we describe an original approach to identify the dominant nonlinear mechanism. This method requires simple transmittance measurements and a fitting procedure. In our suspensions, nonlinearity was identified to be of electronic origin at a 532 nm wavelength, while at 355 nm, it was found in the generation of bubbles.
Highlights
Optical limiting systems are extremely important to protect human eyes or instrumentation in all applications where high-power laser beams are involved
Optical limiting (OL) is referred to as the phenomenon shown by some materials where the energy transmitted through the sample follows two well distinct regimes; at weak input intensities, the light transmitted through the material linearly depends on the intensity of incident radiation
The interest in nanofluids has hugely grown over the last years due to the rapid development of nanotechnology arising in the availability of new nanoparticles and in the development of techniques to disperse them in fluids with improved stability
Summary
Optical limiting systems are extremely important to protect human eyes or instrumentation in all applications where high-power laser beams are involved. Carbon-based nanofluids, in particular those containing nanoparticles belonging to the family of carbon nanotubes (CNTs), have been widely studied for their electronic and thermal properties [13] They show some good optical limiting characteristics, as mentioned above. OL at wavelengths of 1064 and 532 nm was demonstrated for SWCNH dispersed in acetone [19], without, the provision of many details about the investigated samples For this reason, the characterization of the basic properties of these intriguing carbon allotropes being our goal, we focused our study on the systematic investigation of several nanoparticle and colloid parameters (nanohorn morphology, concentration, dimensions of aggregates, sample preparation procedure, and the presence and concentration of surfactants). (4) the formation of vapor bubbles due to interaction with laser photons that we documented widens the future applications of SWCNH-based aqueous nanofluids to direct solar vapor generation and solar desalination systems
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