Third Harmonic Upconverted Full-Stokes Imaging with High-Efficiency Germanium Metasurface from MWIR to SWIR

Abstract

Dielectric resonant metasurfaces can be utilized for efficient high harmonic generation, which has been explored here in this effort for a high-efficient Germanium metasurface for upconverted full-Stokes imaging at 1.33-micron wavelength by the third harmonic generation (THG) from the 4-micron fundamental wavelength. The internal TH conversion efficiency for the Ge film is about 1x10-5 % to 5.6x10-3 % and for the Ge-metasurface 1.5x10-4 % to 1.05x10-1 % for linearly polarized (LP) incidence, and 1.3x10-4 % to 6.1x10-2 % for circularly polarized (CP) incidence, for the optical intensity range 0.47 GW/cm2 to 16.8 GW/cm2 respectively. The effect of the Ge film height variation has been discussed and compared with transmission line theory for the nonlinear medium. The metasurface design pitch is suitably tuned for the anisotropic cross-triangles nanoantenna for analyzing the polarization states of the fundamental beam simultaneously. The effect of source intensity on TH conversion among the LP and CP states, flipping the nonlinear diffraction orders and incipient of new harmonics with intensity dependence and design limitations, has also been addressed. To my knowledge, with this type of metasurface design, this is the first approach for upconverted full-Stokes imaging. The benefit will be upconverted polarimetry of MWIR at SWIR, where uncooled efficient detectors are available for high-resolution thermal imaging. This efficient Ge-metasurface is exempt from TH transmission loss due to the size effect of assigning a phase gradient for polarization-dependent TH diffraction order generation and orthogonal transmission disparity. Integration of this type of metasurface for infrared image upconversion will open new possibilities for intense heat signature identification, especially for target recognition in next-generation infrared homing devices in surveillance and missile defense systems.