An designed output coupler used for the dispersion compensation in Cr:LiSAF femtosecond lasers is reported. It is composed of 50 alternating Ta2O5 and SiO2 layers whose thicknesses are obtained by computer optimization to provide low transmittance and as little as possible group delay dispersion. The optimized output coupler has continuous low transmittance of 1% and group delay dispersion of 0 ±6fs2 from 750nm to 900nm, which can meet the need of dispersion compensation in Cr:LiSAF lasers.
Graphene-CdSe quantum dots hybrid is a promising structure to combine unique properties of graphene and quantum dots. In this work, graphene was firstly prepared on a 300 nm SiO2/Si substrate by mechanical exfoliation of a highly oriented pyrolytic graphite using scotch tape. Then the samples were immersed in CdSe quantum dots solutions for 15 minutes and followed by water flush. The graphene-CdSe quantum dots hybrid structures were obtained due to the electrostatic adsorption of CdSe quantum dots on graphene. Fluorescence quenching of CdSe quantum dots on graphene was found, which probably indicates the energy transfer from CdSe quantum dots to graphene. The results suggest that graphene is a good candidate for manipulating energy transfer of quantum dots due to its extremely high carrier mobility.
Negative dispersion dielectric multilayer mirrors have contributed significantly to the enhancement of the performance, compactness and reliability of femtosecond lasers. There are two alternative approaches that are widely investigated for dispersion compensation: chirped mirrors and Gires-Tournois mirrors. Chirped mirrors can exhibit a broad smooth high reflectance range if the layer thickness is superimposed a quasi-periodic modulation on a linear variation of the optical thickness of the layers. The performance of such chirped mirrors is calculated and the factors affecting the performance are discussed in detail. In such chirped mirrors, the performance is strongly affected by the expected bandwidth and modulation period of the optical thickness of the layers.