Spiral phase infrared imaging with undetected photons using a visible wavelength spatial light modulator.

Imaging with undetected photons utilises induced coherence between downconverted photon pairs in a nonlinear interferometer to record an image of an object using infrared probe photons whilst only detecting photons at an easier-to-detect visible wavelength that never interacts with the object. We show that the induced coherence between photon pairs also allows for manipulation of the Fourier components of infrared light from the object, by implementing phase masks on a spatial light modulator placed in the visible beam. By applying a spiral phase mask to the visible beam we demonstrate a well-known Fourier filtering technique, namely spiral phase-contrast imaging of an object placed in the infrared beam, giving omnidirectional edge enhancement of the image. This approach could also be applied to other Fourier filtering microscopy techniques, such as dark-field and phase-contrast microscopy using undetected photons.