Abstract
The nonlinear refraction of silver nanoparticles (AgNPs) in n-hexane was studied by using the closed-aperture Z-scan technique with a 532 nm nanosecond laser. It was found that, the nonlinear refraction of AgNPs shows the coexistence and transformation from self-focusing to self-defocusing. Specifically, self-focusing occurs at low excitation intensity, self-defocusing occurs at high excitation intensity, and coexistence of self-focusing and self-defocusing occurs at relatively moderate excitation intensity. The experimental results were analysed and discussed in terms of third-order and fifth-order nonlinear refractive effect. Specifically, the self-focusing is caused by the positive third-order nonlinear refraction, the self-defocusing is induced by the negative fifth-order nonlinear refraction, and the transformation from the self-focusing to self-defocusing at medium excitation intensity is caused by the competition of third-order and fifth-order nonlinear refraction. Finally, the third-order refractive index and fifth-order refractive index were obtained.
Highlights
IntroductionThe nonlinear optical (NLO) properties of nanomaterials have been extensively researched due to their applications in the fields of photothermal effect [1], optical sensing [2], photocatalysis [3]
The nonlinear refraction of silver nanoparticles (AgNPs) in n-hexane was studied by using the closed-aperture Z-scan technique with a 532 nm nanosecond laser
The effects of self-focusing, self-defocusing, self-phase modulation (SPM), optical phase conjugation (OPC) and optical bistability caused by nonlinear refraction have broad application prospects in the field of optical limiting [4], optical switching [5], spatial optical soliton transmission [6] and so on
Summary
The nonlinear optical (NLO) properties of nanomaterials have been extensively researched due to their applications in the fields of photothermal effect [1], optical sensing [2], photocatalysis [3]. Nanomaterials 2021, 11, 2485 can be predicted that the high-order and low-order refractive index with opposite symbols will induce self-focusing and self-defocusing; for the third- and fifth-order refractive index, it has been spotted in other materials [11,20,22,23,24]. As far as we know, there are few reports about the transforration at high laser intensity, and they attribute this phenomenon to the action of fifth-order mation and coexistence of self-focusing and self-defocusing induced by the opposite sign nonlinearity. This transition was not seen in the AgNPs experiment of Falcãoof the high-order low-order refractive index for the.
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