The modulation frequency characteristics of the Q-switched envelope in a doubly Q-switched and mode-locked Nd:GGG laser with an acousto-optic modulator (AOM) and Cr4+:YAG saturable absorber are given. At a fixed incident pump power, the repetition rates of the Q-switched envelope and the related laser characteristics versus the modulation frequency of AOM for different small signal transmissions of Cr4+:YAG saturable absorbers have been measured. The experimental results show that the repetition rates of the Q-switched envelope, the average output power, the average peak power, and the pulse widths of the Q-switched envelopes are subharmonics of the modulation frequency at a fixed incident pump power. Furthermore, the mechanism for these behaviors is discussed.
Graphene is used as an ideal platform for plasmonic optical devices due to its unique electrical and optical characteristics. We proposed a unique effective index method to evaluate a graphene-based half Maxwell fish-eye (HMFE) plasmonic lens on a single flake of graphene, which can focus a surface plasmon polariton plane wave and transform into a spherical wave. Similar to traditional optics, the proposed method can be used to investigate the focusing performance of an HMFE lens versus different parameters, including the incident frequencies, the discrete semiring numbers, the chemical potentials, and the size of the proposed lens. In addition, we use two proposed lenses to build an optical-coupling element, which can transform the beam of a plane wave into a different beam width. The proposed effective index method can be used as a reference in designing plasmonic optical devices with a variable effective index profile on a flake of graphene. The finite element method is employed to realize the numerical simulation, which demonstrates results almost consistent with our design methodology.
We study the contribution of Surface-plasmons coupling with a single dipole to enhance the emitter emission. When the
Ag film is inserted into GaN, the emission efficiency of single dipole in GaN can be enhanced greatly. With 3D-FDTD
method, the numerical simulation results demonstrate that the SPs play a key role in enhancement light emitter efficiency.
Furthermore, SPs is sensitive not only to the thickness and refractive index of dielectric, but also to the geometry and
dispersion model of Ag film. By changing the parameters of GaN and Ag film, the location of the enhancement peak of
the emission efficiency in the visible region can be controlled. According to the simply optimal parameters, about 9
times enhancement at 470nm occurs. Our results are of very importance for improving the light-emitting devices of GaN.