Super resolution imaging
The team has studied super resolution techniques by spatial mode overlap. A previous result studied contrast enhancement by direct photon number resolution.
The mode overlap method comes under a family of techniques for resolving incoherent pairs of emitters. When this is done successfully, it is possible to apply the technique to microscopy or astronomy to determine the separation of the point emitters. Our reported technique was based on image inversion via an interferometer. The concept is applicable to distant celestial objects and also to microscopic systems. The concept of using the interferometer is seen in the figure on the left.
It is relatively straightforward to test the concept - one can use a simple laser beam and separate it into two non-interfering beams via a polarizing Mach-Zehnder interferometer. The interferometer performs extremely well in the region of interest - where the separation is within the Rayleigh limit of conventional objectives.
The experimental layout of the interferometer.
In the figure above (a) Measured values of residual power β against set separation for two different degrees of interference. The blue (red) data points have a minimal value of 0.44 (0.22) when the two point sources overlap. For comparison, the theoretical expectation of β for a perfect instrument is provided (solid line). The black vertical line indicates Sparrow’s limit in our experiment. (b) The same data points after subtracting for background. These plots serve as a calibration curve for the instrument. (c) The error in estimated separation,when using conventional error propagation, diverges for small separation. (d) The error in estimated separation, when using the RMSE technique, remains finite even for very small separation.