Dark-field techniques can be used for imaging edge enhancements by parsing the input light through a high-pass filter to select for the high spatial frequencies contribution.
We propose the dark-field separation of optical modes from a thermal point source to enhance the detection of radial asymmetry.
The incident light is spatially filtered through a Mach-Zehnder interferometer with image inversion, outputting the symmetric and asymmetric optical modes into separate channels.
This is successfully demonstrated by up to an order-of-magnitude increase in the signal-to-noise ratio of detecting the asymmetric optical modes.