High-throughput multimodal wide-field Fourier-transform Raman microscope

Abstract

Raman microscopy is a powerful analytical technique for materials and life sciences that enables mapping the spatial distribution of the chemical composition of a sample. State-of-the-art Raman microscopes, based on point-scanning frequency-domain detection, have long (∼1s) pixel dwell times, making it challenging to acquire images of a significant area (e.g., 100×100µm). Here we present a compact wide-field Raman microscope based on a time-domain Fourier-transform approach, which enables parallel acquisition of the Raman spectra on all pixels of a 2D detector. A common-path birefringent interferometer with exceptional delay stability and reproducibility can rapidly acquire Raman maps (∼30min for a 250000pixel image) with high spatial (<1µm) and spectral (∼23cm−1) resolutions. Time-domain detection allows us to disentangle fluorescence and Raman signals, which can both be measured separately. We validate the system by Raman imaging plastic microbeads and demonstrate its multimodal operation by capturing fluorescence and Raman maps of a multilayer-WSe2 sample, providing complementary information on the strain and number of layers of the material.

Generation of interferometrically stable pulse pairs from a free-electron laser using a birefringent interferometer

“…Figure 1 sketches the structure of the TWINS interferometer used in our experiments, equivalent to the systems used in references [6,29,30]. It consists of two birefringent blocks A and B sandwiched between the polarizers P1 and P2.…”

“…Following this approach, some of the authors introduced a birefringent interferometer, the Translating-Wedge-based Identical pulses eNcoding System (TWINS) [27], as a simple and compact optical device which generates two delayed, phase-locked collinear replicas of an input pulse. TWINS has shown considerable experimental versatility and, while originally conceived for two-dimensional electronic spectroscopy [28], it has been further developed and applied to hyperspectral imaging [29], excitation emission spectroscopy, Raman microscopy [30] and even in the combination with high-harmonic generation (HHG) [6]. A schematic of the TWINS interferometer is shown in figure 1.…”

Optical Time-Resolved Microscopy on Few-Atoms-Thick Materials

“…28 Recently, the possibility of spatially resolving the intensity and the spectrum within the excitation profile of a laser beam has been achieved using Fourier transform spectroscopy. 29 Fourier transform spectroscopy allows the parallel recording of spectra for each pixel in a two-dimensional matrix detector, an interesting development for pump−probe spectroscopy.…”

“…The diffusion of the material excitations can be captured either by scanning the probe with respect to a spatially fixed pump or by imaging with a probe that has a spatial extension much larger than the pump . Recently, the possibility of spatially resolving the intensity and the spectrum within the excitation profile of a laser beam has been achieved using Fourier transform spectroscopy . Fourier transform spectroscopy allows the parallel recording of spectra for each pixel in a two-dimensional matrix detector, an interesting development for pump–probe spectroscopy.…”

Enhancing hyperspectral imaging through macro and multi-modal capabilities

“…The TWINS-HSI camera has a spectral resolution adjustable down to 4 nm and, thanks to its common-path arrangement, is interferometrically robust against mechanical vibrations. Thanks to its small power consumption and compact footprint the TWINS interferometer can be embedded in a variety of imaging systems and employed in different configurations [24][25][26][27], including microscopy and in situ analysis platforms.…”