A plasmonic device for gas sensor is investigated for refractive index detection using surface plasmon resonance (SPR). The sensor device consists of nano-cavity antennas formed by metallic rectangular nanostrip array over a metal film, which monitors the changes of the refractive index by measuring the spectral shift of the resonance angle dip. The average detection sensitivity of the gas sensor is about 136 ° / RIU (refractive index units) for SPR excitation at 1550 nm telecommunication wavelength.
A theoretical analysis is presented for third-harmonic generation (THG) in KDP for type I/ type II angle-detuning scheme of high-intensity laser to produce third harmonic radiation near 0.35μm. The effects of the third-order nonlinear susceptibilities (χ<sup>(3) </sup> ), transverse walk-off and diffraction, especially, the effects of third-order nonlinearity and the phase variations on the frequency conversion have been discussed. A split-step algorithm based on the Fast Fourier Transform and fourth-order Runge-Kutta integrator is used. The results shown that the third-order nonlinear interactions decreases the tripling efficiency, and increases of the modulate strength of the output intensity of 3ω radiation. However, adjusting the angular detuning can compensate effectively the effects of third- order nonlinearity. Furthermore 3ω conversion efficiency will drop with the increase of the degree of phase variations, and the improve 3ω conversion efficiency can suppress the 3ω wave amplitude ripples.
Taking into account the effects of third-order nonlinear effects, transverse walk-off and diffraction etc., we have performed theoretical analysis and numerical simulation for third-harmonic generation (THG) in potassium dihydrogen phosphate (KDP). The results show that the efficiency of the THG decreases as the ratio of phase ripples of the input beam increases. The results also indicate that increasing the conversion efficiency of THG can improve the beam quality of the third-harmonic wave.