An imaging system comprises a light source generating a pump beam, and an optical coupling system for receiving an input beam of infrared light from a scene and combining the input beam with the pump beam, wherein an intensity of the pump beam is higher than an intensity of the input beam. The imaging system further comprises a crystal configured for adiabatically mixing the beams and providing an output beam having a frequency which is a sum of frequencies of the input and pump beams, and a visible, near-infrared or ultraviolet light imager configured for collecting and to spectrally resolving the output beam.