9 November 1999 Optical nonlinearity of surface-modified PbS and CdxPb1-xS nanoparticles in the femtosecond regime
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We present an investigation of third-order optical nonlinearity in surface modified PbS and CdxPb1-xS nanoparticles using the Z-scan technique with femtosecond laser pulses at 780-nm wavelength. The samples include PbS nanoparticles in microemulsion with PbS concentration range from 0.3-2.5 X 10-3 M and CdxPb1-xS nanoparticles in microemulsion with x from 0 to 1. An extended Z-scan theory based on the Huygens- Fresnel princeps is employed to extract the nonlinear refraction index from the experimental Z-scan data with a large nonlinear phase shift. The nonlinear refractive index in PbS nanoparticle microemulsion is found to increase linearly with PbS concentration between 0.3 X 10-3 and 1.9 X 10-3 M. The highest concentration microemulsion gives a nonlinear refractive index of 1.8 X 10-11 cm2/W, which is approximately 4 orders of magnitude higher than those of commercially available bulk semiconductors, such as ZnS and CdS, measured at the same conditions. In CdxPb1-xS nanoparticles, Cd0.33Pb0.67S exhibits relatively larger refractive nonlinearity. For all samples, nonlinear absorption remained unmeasureable up to 0.9 GW/cm2. The observed large refractive nonlinearity in these nanoparticles may mainly be attributed to the optical Stark effect and contribution from the surface-trapped states in the nanoparticles.
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He Ping Li, B. Liu, Chan Hin Kam, Yee Loy Lam, Wenxiu Que, L. M. Gan, C. H. Chew, and G. Q. Xu "Optical nonlinearity of surface-modified PbS and CdxPb1-xS nanoparticles in the femtosecond regime", Proc. SPIE 3899, Photonics Technology into the 21st Century: Semiconductors, Microstructures, and Nanostructures, (9 November 1999); doi: 10.1117/12.369423; https://doi.org/10.1117/12.369423

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