OPTICAL POWER LIMITING MATERIALS BASED ON CARBON NANOSTRUCTURES:
PROGRESS AND PROBLEMS
I.M. Belousova1,2, S.K. Evstrop’ev3, I.M. Kislyakov2,1*, V.M. Volynkin1,3
1Vavilov State Optical Institute, St. Petersburg, Russia
2St.Petersburg National Research University of ITMO, St. Petersburg, Russia
3Research Technological Institute of Optical Material Science (NITIOM), St. Petersburg, Russia
*Corresponding author: iv.kis@mail.ru
Application of carbon nanostructures for optical power limiting (OPL) is widely studied. Among the nanoobjects using as OPL materials the most applicable are carbon nanopowder in form of carbon black suspensions (CBS), multi-walled and single walled carbon nanotubes (MWCNT and SWCNT), and fullerenes C60, C70 and higher. Earlier we have reported an application of polyhedral multi-shell carbon nanoparticles (“Astralenes”) for the OPL.
The physical mechanism of nonlinear OPL effect in these nanostructures is different. The main process in fullerene-based materials under the action of powerful laser radiation in visible spectral range is reverse saturable absorption (RSA) determined by features of their triplet electronic levels. The well-known mechanism of OPL in CBS and suspensions of large nanostructures (CNT, Astralenes and others) is nonlinear scattering (NLS) on bubbles growing around irradiated nanoparticles and on forming plasma. The scattering is more broadband and even more effective than the RSA, however attempts of an application of NLS structures in solids strike against comprehensible difficulties.
RSA active particles on the contrary are workable in solids. Now there are results reported of nonlinear optical response in some solids with carbon nanotubes encapsulated where the reason of nonlinearity is probably a charge transfer between nanotube and its microenvironment. However the common problem of solid limiters is the necessity of a withdrawal of an excess energy that may cause damages of solid matrix and limits its dynamic range.
In liquids this problem is absent because however high the radiation energy is damages that it cause dissipate. The time of these dissipations vary with liquid and depends on its viscosity, heat of evaporation and other thermodynamic properties. For the ordinary solvents like water or ethanol this time is several seconds that’s why suspensions of carbon nanostructures in these liquids are getting bleached under the action of powerful laser radiation in pulse-periodic mode with repetition rate > 0.1 Hz that also limit the dynamic rage of these materials.
After performed studies of a variety of organic solvents we show a possibility to expand the scope of limiters based on carbon nanoparticles to the pulse-periodic laser repetition frequencies up to 10 Hz and higher. By the example of an introduction of carbon nanoparticles into a solidifying silica xerogel composite we show that in process of an optical material solidification the limiting parameters does not undergo changes except a drastic drop of the radiation resistance. Advanced results of an application of self-recovering polymers as solid matrices for increasing the dynamic range of the OPL are shown.
The other question that is not yet clear for limiters on carbon nanoparticles: is the nanoparticle type affect on limiting parameters.
It is well known that for dispersions of all the carbon particle species from fullerenes to large and heavy clusters the threshold of nonlinear response is approximately the same and have the order 108 W/cm2. Nevertheless, differences in OPL behavior should appear since its mechanisms are different. So, we can obtain different nonlinear optical characteristics of effects using plasmonic resonance of metallic nanotubes, pseudo-discrete structure of SWNT electronic states etc.
As a result of performed studies of the effect of the nanotubes composition and properties in material on the limiting characteristics ways of the attenuation coefficient increasing in these materials were found. In particular, at the wavelength 532 nm of nanosecond pulse radiation the attenuation factor was increased from several tens to several hundred with 1.5 mrad observation. The compositions are stable during a year and maintain its spectral and nonlinear optical properties in a broad temperature range (from –40°C to +50°C).
The developed during last few years new approaches to composition of materials based on carbon nanostructures show prospects of its application for a construction of universal limiters of laser radiation in visible and near IR spectral range.
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