Influence of PVP polymer concentration on nonlinear absorption in silver nanoparticles at resonant excitation

Silver nanoparticles exhibit saturable absorption at resonant excitation, which upon addition of the polymer as a capping agent, exhibit reverse saturable absorption. These nonlinear optical processes play an important role in the overall nonlinear optical properties of silver nanoparticle. Thus, with this viewpoint, the nonlinear absorption of silver nanoparticles in deionized water in the presence of varying concentration polyvinylpyrrolidone polymer was investigated using femtosecond laser pulses at 400 nm. This study shows that the saturable absorption process is significantly suppressed at high concentration of the polymer. The silver nanoparticle with smaller size shows pure reverse saturable absorption process with the respective coefficient of beta = 7.55 x 10(-12) cm/W. The change in the nonlinear optical response from combined saturable absorption and reverse saturable absorption to pure reverse saturable absorption process was observed as the concentration of polymer increases.