Fig. 8: The thickness detection based on the proposed infrared imaging technique via FWM.
From: Broadband infrared imaging governed by guided-mode resonance in dielectric metasurfaces
a The images of several glass chips (BK7) overlapped together under white light source illumination. bi–biiii The transformed images show that the nonlinear emissions occur on different area of different layers depending on the moving distance of the delay line (shown below). c The normalized density of the FWM emission with the length of the time delay
