We present an investigation of third-order optical nonlinearity in surface modified PbS and Cd$-x$/Pb$- 1$MIN@x$/S 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 $MUL 10$+$MIN@3$/ M and Cd$-x$/Pb$-1$MIN@x$/S 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 $MUL 10$+$MIN@3$/ and 1.9 $MUL 10$+$MIN@3$/ M. The highest concentration microemulsion gives a nonlinear refractive index of 1.8 $MUL 10$+$MIN@11$/ cm$+2$//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 Cd$-x$/Pb$- 1$MIN@x$/S nanoparticles, Cd$-0.33$/Pb$-0.67$/S exhibits relatively larger refractive nonlinearity. For all samples, nonlinear absorption remained unmeasureable up to 0.9 GW/cm$+2$/. 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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机译：我们在表面改性PBS和CD $ -X $ / PB $ - 1 $ MIN @ $ / s纳米粒子上展示了三阶光学非线性的调查，使用了780nm波长的飞秒激光脉冲的Z扫描技术。所述样品包括纳米的PbS在用PBS浓度范围从微乳液0.3-2.5 $ MUL 10 $ + $ MIN @ 3 $ / M和Cd $ $ -x /铅$ $ -1 @ MIN X $ / S纳米颗粒在微乳液，其中x从0到1.基于Huygens-Fresnel Princeps的延伸Z扫描理论用于从实验性Z扫描数据中提取具有大的非线性相移的实验性Z扫描数据的非线性折射指数。发现PBS纳米粒子微乳液中的非线性折射率与PBS浓度线性增加0.3 $ MUL 10 $ + $ MIN @ 3 $ /和1.9 $ MUL 10 $ + $ MIN @ 3 $ / M.最高浓度的微乳液给出非线性折射率为1.8 $ mul 10 $ + $ min @ 11 $ / cm $ + 2 $ // w，比商业上可用的批量半导体（如ZNS和CD）高约4个级）相同的条件。以CD $ -x $ / pb $ - 1 $ min @ x $ / s纳米盖，CD $ -0.33 $ / pb $ -0.67 $ / s展示相对较大的屈光非线性。对于所有样品，非线性吸收仍然不可估量，高达0.9 GW / cm $ + 2 $ /。在这些纳米颗粒中观察到的大的屈光非线性可以主要归因于纳米颗粒中的光学凝固效应和从表面捕获状态的贡献。
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