In this novel multimodal wide-field Raman microscope, spectra are obtained by the time-domain Fourier-transform method. The wide-field approach enables faster collection of Raman maps, while the time-domain method disentangles fluorescence and Raman signals. This is obtained by choosing a proper sampling of the interferogram, thanks to the use of an ultrastable common-path birefringent interferometer. Validation of the system is performed on plastic microbeads; multimodality is demonstrated by fluorescence and Raman maps of a few-layers transition metal dichalcogenide sample.
We present a novel wide-field Raman microscope, based on the time-domain Fourier-transform method. This enables parallel acquisition of Raman spectra on all the pixels of the 2D detector; the resulting wide-field approach allows faster collection of Raman maps with respect to standard raster-scanning methods. In addition, the time-domain method disentangles fluorescence and Raman signals. The system is robust and stable, thanks to the use of an ultrastable common-path birefringent interferometer. Validation of the system is performed on plastic microbeads and on a few-layers transition metal dichalcogenide sample.
Spectral imaging is a method to acquire the spectrum of the light for each point in the image of a scene. By combining classical imaging with Fourier-transform spectrometry it is possible to acquire hyperspectral images with higher spectral accuracy and lower times compared to standard dispersive optical systems. The technique is based on interferometry and is hence technically challenging as it requires to generate field replicas with delay controlled within a small fraction (1/100 or better) of the optical cycle. Standard FT spectrometers are heavy, cumbersome and too sensitive to mechanical and thermal perturbations for use in portable devices or for deployment in space applications. Here we propose and experimentally validate a compact FT-based hyperspectral camera, in which the FT module is an innovative ultra-stable birefringent common-path interferometer (the Translating-Wedge-Based Identical Pulses eNcoding System, TWINS). TWINS has intrinsic interferometric stability, it is lightweight and is ultracompact, making our FT-based hyperspectral camera an ideal device for portable on-field and spaceborne applications. Our prototype camera is able to measure absolute reflectance and fluorescence with very high spectral accuracy in the visible and near-infrared spectral range and can be extended to the spectroscopically rich thermal infrared range (3 mu;m to 14 μm) using suitable birefringent materials and detectors. We present some examples of application in the visible and TIR ranges.
In this work we present a novel hyperspectral camera based on a compact birefringent interferometer to perform reflectance measurements on works of art.
The innovative aspect emphasized in our system lies the capability to acquire hyperspectral images of the sample at different magnification, allowing to image a field of view ranging from few millimetres to tens of centimetres.
With our work, we want to demonstrate the effectiveness of this system when performing hyperspectral imaging of painted surfaces at the macro scale, i.e., with few millimetres of field of view, and discuss its potential to resolve the details of a painting as pigments’ grains.
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.
The investigation of artworks of cultural heritage is generally aimed at the characterization of the constituent materials and the evaluation of their state of conservation. Research may shed light on the pigments and their potential deterioration mechanisms, and on the conservation treatments. Laboratory analysis on micro-samples taken from the artwork is still an invaluable practice for a deep understanding of the paint layer composition. In this context, a powerful technique is spectral microscopy, which acquires the spectrum for each point in the image of a sample. To acquire a continuous spectrum, one very efficient method is based on Fourier-transform (FT) spectroscopy as it allows massive parallelization on all the image pixels. Here we introduce a hyperspectral microscope based on an innovative FT spectrometer; the device is compact, robust, with high throughput and broad spectral coverage. In our microscope, light is collected by an infinity-corrected objective, propagates in the innovative spectrometer and is imaged on a silicon monochrome CMOS camera by a tube lens. The typical spectral resolution of the microscope, which can be flexibly adjusted for each measurement, is 3 THz (4 nm at 600 nm). We show very compact implementations of the hyperspectral microscope and their use for wide-field imaging of reflection, fluorescence and, interestingly, fluorescence-free Raman spectra. Thanks to the high throughput, the acquisition time of our microscope is significantly shorter than traditional raster-scanning approaches.
We introduce a Fourier-transform hyperspectral microscope based on an ultrastable birefringent interferometer. The microscope enables wide field acquisition with broad spectral coverage, tunable spectral resolution, high sensitivity and short acquisition time. We present the prototype of an add-on to a commercial microscope. We provide examples of applications in biology and solid state physics. The microscope is suited for fluorescence and Raman imaging.
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