Compared with bulk materials, the corresponding metal nanoparticles have different optical and nonlinear optical effects. The research and analysis show that the properties of nanostructures with different sizes or shapes are different when the materials are the same. For Au nanoparticles, their SPR absorption bands can be tuned throughout the visible spectrum by changing the size and shape of nanoparticles. In this paper, the optical properties of gold nontriangular structures have been studied by finite difference time domain (FDTD) method. The effects of size, thickness and dielectric constant of gold nanometer triangle on its absorption spectrum were discussed. There are three absorption peaks in the cash nontriangular structure. When the thickness is the same (20nm), with the increase of the size of the gold triangular prism structure, the three absorption peaks shift red, the red shift speed increases gradually, and the absorption coefficient increases in turn. The red shift velocity of the main peak absorption peak is stronger than that of the secondary absorption peak. Under the same size structure (100nm), with the increase of gold nanometer triangle thickness, the main absorption peak shifts blue and the absorption coefficient decreases in turn. When the size and thickness are the same, with the increase of dielectric constant, the three absorption peaks shift red, and the absorption coefficient decreases in turn.
A plasmonic sensor which can detect the refractive index and the polarization of incident light is proposed. The sensor is based on a gold composite structure constructed from a gold film which was etched a plurality of circular arc-shaped slits. The transmission spectra of the composite structure are theoretically studied using the finite-difference time-domain method (FDTD), and the influence of structure parameters on the transmission spectra are also studied. Moreover, it was found that the transmission spectra of are sensitive to environment refractive index, which can be used to detect refractive index. Specifically, the sensitivity of 550 nm/RIU was obtained after optimizing the structure parameters. Due to the asymmetry of the sensor structure, this design can also detect the polarization direction of light.
The nonlinear absorption properties of spherical silver nanoparticles (AgNPs) with average sizes of 15nm and 30 nm were studied by Z-scan technique. The experimental results show that under the same excitation conditions, both samples show the switch behavior from saturable absorption (SA) to reverse saturable absorption (RSA). The research results show that, SA is caused by plasma bleaching of ground state, and the RSA results from free-carrier absorption. And nonlinear properties of AgNPs is size-dependent. The estimated values of 𝐼𝑆 were 1.62 × 1011𝑊⁄𝑚2 and 2.40 × 1011𝑊⁄𝑚2 for AgNPs with size 15nm and 30nm, respectively, where as the corresponding β values were 0.56 × 10−10 𝑚⁄𝑊 and 1.17 × 10−10 𝑚⁄𝑊. Besides, the ultrafast dynamics of the AgNPs was studied using white-light pump-probe technology. The experiments show that the process includes a slow decay and fast decay process. The theoretical values of slow decay were 5.5ps and 3.1ps for 15nm AgNPs and 30nm AgNPs, respectively, and the corresponding fast decay process values were 20ps and 55ps. The research results show that the ultrafast dynamics of AgNPs is size-dependent. The slow process was due to the electron-phonon coupling, and the fast process is due to the phonon-phonon coupling.
We propose an innovative structural design based on a metamaterial absorber in the terahertz band. And verified the absorption curve of the new structure by using FDTD software simulation. The absorption curves of the light source at different incident angles and polarizations were simulated.The simulation results show that the multi-layer covering structure effectively increases the absorption bandwidth of the metamaterial absorber in the terahertz band. And the absorption curve is higher and flatter.
The optical limiting performance of platinum nanoparticle protected by C60 derivative in chloroform, ethanol and dimethylformamide (DMF) was measured with 532nm, 8ns duration laser pulses. Experiments showed that the optical limiting is solvent-dependent. The origins and solvent effect of the optical limiting were analyzed. It was proposed that the absorption-induced scattering is the main mechanism causing the optical limiting behavior and solvent effect.
We investigate the formation of ripple and nanohole induced by femtosecond laser pulses on the surface of silicon. Periodic ripples aligned perpendicular to the direction of laser polarization has been observed. The period of the periodic ripples decreases with the increasing pulse number. Particularly aperiodic ripples with orientation parallel to the laser polarization are formed depend on the number of laser pulses and energy. The nanohole arrays are formed on the overlapped areas of periodic and aperiodic ripples. The interference between the surface scattered or excited wave and the laser itself is proposed to explain the decrease of ripple period.
In this paper, we demonstrated the fabrication of laser-induced holes in the gold film of 50nm thickness using 120fs laser pulses at 800nm wavelength in air environment. The surface morphologies¬microstructures and diameters of holes were characterized using atomic force microscopy (AFM). It was found that, there are two kinds of thresholds of laser fluence for the formation of holes. And the diameters of holes were influenced by pulse energy and shot numbers. Based on the investigation above, the origin of the holes was discussed.
The propagation and split of the filamentation of femtosecond pulses in air have been paid much attention since last a few years. However, most research works are performed with few considerations of the turbulence effects of atmosphere due to the difficulties of utilizing analytical solutions and experiment conditions. In this work, we will attempt to introduce a kind of numerical simulation method to analyze the transmission features of femtosecond laser pulses in air or in the turbulent air, namely, it is called multi-phase screen method (MPSM) which use phase screen to simulate atmospheric turbulence. In this presentation, the main laser parameters are as follows: 85 fs pulse-width, 0.8cm radius of the beam, the two kinds of 160GW and 1.0 TW peak-power operating at 800 nm. Then utilizing the structure of Vortex soliton to control the filamentation is proposed. In our cases, four Gaussian pulses with a difference of π/2 in the phase of each adjacent beam as a ring to control the filamentation by utilizing its characteristics of the vortex soliton. Some results show that the coupling and interaction among four Gaussian pulses cause the rotational transfer of the energy of the four beams. Finally, we obtain the transmission features of the beams propagating in the turbulent air with different intensities by the MPSM.
Nonlinear optical properties of femtosecond laser-induced micro-structures containing gold nanoparticles in silicate glasses were investigated by using Z-scan technique with 8ns pulses at 532nm. Optical limiting effects of such structures were also measured. The experimental results were found to be significantly variable for the microstructures under different induction conditions. Strong optical nonlinearities in these yielded structures can be attributed to the surface plasmon absorption of gold nanoparticles precipitated in glasses. These microstructures exhibiting large optical nonlinearities are inferred to be useful for the fabrication of integrated ultrafast optical switching and laser protection devices.