Self-illuminated third-harmonic image upconversion

We demonstrate third-harmonic upconversion imaging to visualize real time infrared images in the visible with standard CCD or CMOS silicon-based cameras operating at room temperature. Different from the usual sum-frequency mixing image upconversion, our third-harmonic image upconversion approach does not require an auxiliary IR source to illuminate a target. The upconversion system uses a passively Q-switched Nd³⁺:YVO₄ laser operating at 1342 nm with two intracavity KTP crystals, obtaining a 447 nm upconverted image by a cascaded process where an upconverted image at 671 nm is also obtained as an intermediate step.