Hybrid optical imaging with near-infrared, mid-infrared, and terahertz wavelengths for nondestructive inspection [Invited].

Optical imaging is a powerful tool for nondestructive inspection, with high spatial resolution and low invasiveness. As light-material interactions vary a great deal depending on the wavelength, it is difficult to select the best imaging wavelength without prior knowledge of the optical properties of the material. To overcome this difficulty, we constructed a hybrid optical imaging system using three different wavelengths: near-infrared (NIR), mid-infrared (MIR), and terahertz (THz) regions. The same imaging optics were integrated with different light sources and detectors. Depending on the light-material interaction and detection sensitivity, NIR and THz imaging indicated some potential for nondestructive inspection, but MIR imaging showed difficulty. A combination of NIR and THz imaging will be a powerful tool for optical nondestructive inspection.