A high-throughput Hyperspectral Microscope based on a Birefringent Ultrastable Common-Path Interferometer

Spectral microscopy is a method to acquire the spectrum for each point in the image of a sample. The most straightforward technique uses spectral filters to collect a sequence of images at a discrete number of spectral bands, leading to discrete spectra. A more complete spectral characterization is hyperspectral microscopy, which acquires the whole continuous spectrum of each point of the image. A powerful approach to this aim is Fouriertransform (FT) spectrometry [1] , [2] , in which an optical waveform is split by an interferometer in two delayed replicas, whose interference pattern is measured by a detector as a function of their delay. The FT of the resulting interferogram yields the continuous intensity spectrum of the waveform. The FT approach is able to retrieve in parallel the spectra for all pixels in a scene and is hence well suited for wide-field and fluorescence microscopy. Moreover, its intrinsic high throughput properties makes it applicable to the detection of weak signals, such as Raman ones. However, the FT approach is also very challenging, as it requires controlling the delay with sub-cycle precision. Here we report on a novel hyperspectral microscope (HSM) based on the FT approach (FT-HSM) and using a compact, highly stable common-path birefringent interferometer, a version of the Translating-Wedge-based Identical pulses eNcoding System (TWINS) [3] , [4] . Figure 1(a) shows the schematic setup of the microscope. Light is collected by an infinity-corrected objective and imaged on the 2D detector (14-bits, silicon monochrome CMOS camera) by a tube lens; the TWINS interferometer is placed between the tube lens and the detector. The spectral resolution of the interferometer is inversely proportional to the adjustable total phase delay. Our interferometer setup introduces a delay of ±250 fs at λ = 600 nm and corresponds to spectral resolution of 3 THz (~4 nm), which can be increased if required.