High-sensitivity hyperspectral Fourier-plane microscopy by an innovative common-path interferometer

Fourier-plane optical microscopy is a powerful technique for studying the angularly-resolved optical properties of a plethora of materials and devices. The information about the direction of the emission of light by a sample is extracted by imaging the objective back focal plane on a two-dimensional detector, via a suitable optical system. This imaging technique is able to resolve the angular spectrum of the light over a wide angular field of view, but typically it doesn’t provide any spectral information, since it integrates the light intensity over a broad wavelength range. On the other hand, advanced hyperspectral imaging techniques are able to record the spectrum of the transmitted/reflected/emitted light at each pixel of the detector. In this work, we combine an innovative hyperspectral imaging system with Fourier-space microscopy, and we apply the novel device to the characterization of planar organic microcavities. In our system, hyperspectral imaging is performed by Fourier-transform spectroscopy thanks to an innovative common-path birefringent interferometer: it generates two delayed replicas of the light field, whose interference pattern is recorded as a function of their delay. The Fourier Transform of the resulting interferogram yields the intensity spectrum for each element of the microscope angular field-of-view. This system provides an angle-resolved hyperspectral view of the microcavities. The hyperspectral Fourier-space image clearly evidences the cavity modes both in photoluminescence and reflection, whose energy has a parabolic dependence on the emission angle. From the hyperspectral image, we reconstruct a 3D view of the parabolic cavity dispersion across the whole Fourier space.