中文摘要：

以脉宽为50fs、波长为800nm、重复频率为1kHz的飞秒激光作为激发光源，利用z扫描技术研究了CdSeS量子点（QDs）／聚苯乙烯（PS）复合薄膜在非共振区的三阶非线性光学特性。实验结果表明，CdSeSQDs／PS复合薄膜在800nm光的激发下具有较大的非线性吸收效应；观察到随着激光强度的增加，复合薄膜从饱和吸收（SA）向反饱和吸收（RSA）转变。该反饱和吸收效应主要源于CdSeS量子点的双光子吸收（TPA）。并且，双光子吸收系数卢随着激光强度的增加而增加。当激光强度为4．2Gw／cm。和16．8GW／cm^-2时，β分别为1．6×10^-8cm／W和2．8×10^-8cm／W，与已报道的量子点相比较高出1个数量级；非线性折射率n2分别为-6．2×10^-11cm^2／W和2．7×10^-12cm^2／w，与已报道的量子点相比较高出2个数量级。结果表明，CdSeSQDs／PS复合薄膜在光开关和光限幅等方面具有较大的潜在应用价值。

英文摘要：

The off-resonant nonlinear optical properties of the composite film of CdSeS quantum dots （QDs） stabilized in polystyrene （PS） nanosphere are investigated by Z-scan technique with femtosecond laser （800 nm, 50 fs, 1 kHz）. It is observed that the signs of the nonlinear absorption coefficients and refractive indices changes from negative to positive with laser intensity increasing, which is due to the transition from saturable absorption to two-photon absorption （TPA）. With laser intensity of 4.2 GW/cm2 and 16.8 GW/cm2 , the two-photon absorption coefficient （β） are 1.6 × 10-8 cm/W and 2.8 × 10 8 cm/W, respectively, and the third-order nonlinear refractive indices （ n2 ） are -- 6.2 × 10-11 cm2/W and 2.7 × 10 ^-11 cm2/W, respectively, which shows an increase of about one magnitude for β and two magnitudes for n2 compared with previous reports. The results indicate that CdSe QDs doped PS has high potential application value for all-optical switching devices.