To analyze the terahertz (THz) wave generation by the mid-infrared (MIR) frequency nondegenerate parametric downconversion (NPDC) process in graphene nanoribbon arrays (GNAs) the nonlinear simulations using the perturbation method for solving the nonlinear diffraction problems were performed. First, we find the resonant frequencies of surface plasmon polaritons (SPP) modes in GNAs using the calculated multimode linear absorption spectra of incident waves with s-, p-polarization. Then we select the graphene ribbon sizes to satisfy the excitation condition of the SPP modes in the MIR frequency range. We choose the frequencies of pump and signal waves equal to resonant frequencies of the fundamental and high order SPP modes of GNA, respectively. It is shown that the efficiency of the THz wave generation via frequency NPDC of MIR to THz by nonlinear graphene arrays increases by several orders of magnitude when the frequency of signal and pump waves are close to the resonant SPP mode frequencies.
A multilayer two-dimensional periodic metasurface made of graphene micro-ribbons, which absorbs almost 100% of the energy incident on it at the resonance of the surface plasmon-polariton, has been theoretically investigated. To increase the bandwidth of the device, it is proposed to place 2-3 parallel graphene ribbons with close lengths in one elementary cell of the metasurface. It is shown that at resonance frequencies the generated power of the third harmonic increases by several orders of magnitude and can be increased in comparison with single-layer structures with an increase in the number of layers and packing density of graphene microribbon arrays and when using multilayer substrates.
The development of chirped pulse amplification lasers toward multi-PetaWatt power imposes more demands on laser system elements. To make the spectral band of pulse compressors wider, laser designers began to consider Littrow mounted grating setups. In this study we investigate two Littrow type configurations. The first one is roll - a grating is rotated in the grating plane by a small angle. The second configuration is pitch - a grating is rotated by small angle about an axis perpendicular to the grating grooves. In this paper we experimentally measured diffraction efficiency of rolled and pitched dielectric grating, and simulated it with two methods: numerical Fourier Modal Method in LightTrans Virtual Lab and semi-analytical Volume Integral Equation Method. Here we claim that roll is more preferable for dielectric diffraction gratings with high groove density. It is shown that the energy of laser pulse compressed by a Littrow-roll configured compressor is 2 to 5% higher than Littrow-pitch configured one.
A diffraction grating based on all-dielectric multi-layer structure is designed for compression of ultrafast pulses with spectrum centered at 900 nm. The grating at Littrow angle with an out-of-plane configuration shows more than 96% efficiency over the reflective band of 100 nm for the angle of incidence 41 degrees. We suggest grating grooves and the very first layer under the grooves to be made of fused silica. Reflective mirror under corrugated layer is designed as a stock of three types of dielectric nanolayers. Tolerances for groove depth and angle of incidence are estimated and, optimal duty-cycle parameter is found out. Electric field distribution inside of the grating is also numerically studied. The model is simulated by two methods: numerical Fourier Modal Method in LightTrans Virtual Lab and semi-analytical Volume Integral Equation Method. The results obtained by both methods show an excellent agreement.
All-dielectric grating with more than 98% efficiency over the reflective band of 40 nm with the central wavelength at 1053 nm is simulated for the angle of incidence 72 degrees. For the grating design we used the fact that chirped mirrors give wider reflective band than usual quarter-wavelength dielectric mirrors. Grating grooves and the very first layer under the grooves in our model is made of fused silica; underneath of the top layer we placed a chirped stack of 13 HfO2/SiO2 layers. Tolerances for groove depth and angle of incidence are estimated, optimal duty-cycle parameter is found out. Electric field distribution inside of the grating is also numerically studied. The model is simulated by two methods: numerical Fourier Modal Method in LightTrans Virtual Lab and semi-analytical Volume Integral Equation Method. The results obtained by both methods show excellent agreement.
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