Second harmonic wave generation in ununiform microwave plasma by metamaterial effect

We performed the monitoring of plasma parameters and intensity of second harmonic (SH) wave in the composite of microwave overdense plasma and the metamaterial under the various conditions; input power, gas pressure and the position of the detection. Plasma has been dealt with the nonlinear optical material because of the inherent nonlinearity based on the complex motion of particles in plasma. Moreover, generation of ions from plasma is important for many industrial processes. However, electron density $n_{\mathrm{e}}$ provides the threshold frequency $\omega_{\mathrm{pe}}$ and the electromagnetic (EM) wave cannot penetrate into rich-$n_{\mathrm{e}}$ plasma when the frequency is under $\omega_{\mathrm{pe}}$; plasma permittivity ($\varepsilon )$ becomes negative. We introduced double-split-ring resonators (DSRRs), one of metamaterials, which macroscopically have negative permeability ($\mu )$ by the magnetic resonance, and canceled the negative $\varepsilon $. Our previous report [1] included the rough results about SH wave generation and $n_{\mathrm{e}}$ in terms of the monitoring positions. In this report, we show the relation between the propagation of the input wave (2.45 GHz), SH wave and parameters of generated plasma in detail, and clarify the microscopic effect of DSRRs [1] A. Iwai, Y. Nakamura, and O. Sakai, Phys. Rev. E, 92 (2015) 033105.