Calculation of the efficiency of doubling the radiation of a sub-THz gyrotron dueto lattice nonlinearity in a single crystal InP plate

In this work, we calculated the efficiency of second harmonic generation for sub-THz gyrotron radiation in a single-crystal InP plate embedded in a conical metal waveguide. For values of losses at the doubled frequency (depending on the degree of purity of the InP crystal), the dimensions of the wafer are revealed that provide the optimal effective frequency conversion. Thus, the conversion factor $f\to2f$ can reach 5 W/kW$^2$ when pumped at the frequency of 263 GHz and the loss of $\alpha_{2f}$ = 0.1 cm$^{-1}$. The possibility of a noticeable increase in the efficiency of frequency doubling with fine tuning of the phase matching due to the selection of the size of the submicrometer gap between the InP plate and the plates of the metal waveguide is shown. The results obtained can be used to solve applied problems in the field of dynamic nuclear polarization spectroscopy and nuclear magnetic resonance studies.