In this contribution we introduce a compact version of a broadband static Fourier transform spectrometer (bs- FTS) for the mid-infrared spectral range. The bsFTS covers a spectral range from about 4.5 µm to 14 µm, respectively 2220 cm−1 to 700 cm−1 at a spectral resolution of 8 cm−1. As, in contrast to scanning Fourier trans- form spectrometers, the interferogram is modulated not over time but in the spatial domain, the measurement speed is only limited by the detector. This allows for infrared spectroscopy at 25 Hz to 200 Hz using uncooled microbolometer arrays. Besides liquid measurements in attenuated total reflection (ATR), demonstrating the accuracy and linearity of the bsFTS, we show time-resolved analyses of 1,1,1,2-Tetrafluoroethane (R134a) and carbon monoxide test gases to prove the suitability of the system for high-speed spectroscopy.
Hyperspectral imaging microscopy is a powerful analytical tool for spatial identification and spectral feature extraction in chemical and biological complex systems. Inspired by super-resolution microscopy, structured programmable projection coupled with spectral image reconstruction techniques is employed to improve the spatial resolution of spectroscopic imaging microscopy. In this work, a line-scan hyperspectral imaging microscope implemented with a digital light projector (DLP) was demonstrated. The DLP with a digital micromirror device (DMD) was used to project sinusoidal fringes with three angular orientations and three phase shifts. After synchronization of fringe projection, stage movement, and image acquisition, hyperspectral data sets were acquired, and image reconstruction was conducted using the nine-frame images for improved spatial resolution over the full wavelength range. This work contributes to the progress in microscale and nanoscale imaging using line-scan hyperspectral microscopy.
Two-dimensional van der Waals materials are attractive for photonics and optoelectronics due to distinctive layerdependent optical properties. Optical properties based on light-matter interactions have been revealed by modern imaging and spectroscopy techniques. Hyperspectral imaging microscopy working in line-scan mode (push-broom microspectroscopy) can provide abundant spectral information covering a large area compared to conventional spectroscopy techniques, with a higher acquisition speed than point-scan techniques such as atomic force microscopy and Raman imaging microscopy. This contribution studies in-depth the reconstruction of 3D datacubes and the extraction of optical responses of the sample. Monolayer MoS2, a subclass of semiconducting two-dimensional materials, is fabricated by the mechanical exfoliation method on the SiO2/Si substrate with an oxide thickness of 285 nm. The isolated monolayer MoS2 is observed and identified by a conventional optical microscope. The custom-built push-broom microspectroscope is utilized to scan the region of interest, with the whole spectrum of every line recorded at each frame. The spectral information of every point is collected and 3D spectral data sets are reconstructed for feature extraction and property analysis. To realize the thickness mapping of flakes, linear unmixing is employed to calculate the abundance of isolated monolayer MoS2 on the SiO2/Si substrate, improving flake identification performances. The characteristic spectrum of monolayer MoS2 is acquired by averaging the spectrum from the monolayer MoS2 flake. Furthermore, the optical dielectric response is further analyzed by Kramers-Kronig constrained analysis and Fresnel-law-based analysis. The optical dielectric function is calculated and compared based on the refractive index and medium thickness. This detailed analysis of optical dielectric responses highlights the feasibility of push-broom microspectroscopy for two-dimensional materials characterization.
In this contribution we present a broadband static Fourier transform spectrometer (bsFTS) based on a single- mirror interferometer containing only off-the-shelf optical components and an uncooled microbolometer detector
array. The system uses concave mirrors instead of lenses and therefore covers a wide spectral range from 3.6 μm to 17 μm at a spectral resolution of 12 cm-1. Furthermore, dispersion effects can be minimized and the system can thus be designed with increased temperature stability. We demonstrate the optical and mechanical design of
the current laboratory prototype and compare the instrument to a scanning Fourier transform infrared (FTIR) spectrometer. Additionally, we present a technique for simultaneously acquiring the sample spectrum and the background spectrum. Thereby, a variation of the background over time can be compensated continuously and hence the bsFTS presented in this contribution offers significant potential with regard to long-term stability.
Due to excellent optical performances, two-dimensional materials have emerged as promising materials for applications like optoelectronic devices, photonic devices, and optical sensors. To better study the unique optical performances of 2D materials, spectroscopy techniques such as reflectance and transmittance spectroscopy, and Raman spectroscopy have been utilized for image acquisition and optical property analysis. Hyperspectral imaging (HSI), a combination of spectroscopy and imaging technique, has been used for characterization and property analysis of new materials. A 3D datacube with the wavelength as z-axis, plus spatial axes x and y, can be acquired, and the spectral information can be extracted for characteristic analysis. With the high demand for area imaging of 2D materials, a microscopic HSI setup with a LED light source working in the visible range was proposed for 2D MoS2 imaging. The HSI imager using a reflection grating works in line-scanning mode in the range of 380-1000 nm. A 3D datacube of 2D layered MoS2 was built and processed for thickness measurement and optical property analysis, including single-band analysis of the imaging area, spectral analysis of the interesting area, and comparison with the image acquired by a white-light microscope. Finally, general performances of hyperspectral imaging of 2D MoS2 in the visible range was analyzed and discussed for further optical applications
Hyperspectral imaging is an established technique for process analysis capturing a two-dimensional spatial image and the spectral information for each pixel simultaneously. When moderate spectral resolution is sufficient, static imaging Fourier transform spectrometers (sIFTS) can offer a viable alternative to their scanning counterparts in the mid-infrared spectral range. Therefore, in this paper we present a sIFTS concept based on a single-mirror interferometer which shows no internal light losses and still works with extended light sources, achieving sufficient signal-to-noise ratios. The interferometer consists of a beam splitter, a plane mirror and a lens, which makes it both inexpensive and relatively easy to adjust. For a proof of principle we present a transmission measurement setup including a light source module, imaging optics and a single-mirror interferometer. The system achieves a spectral resolution of 12 cm−1 in a spectral range from 2700 cm−1 to 800 cm−1 , respectively from 3.7 μm to 13 μm. The spatial resolution amounts to about 10.10 lp/mm, the results for a sample containing different polymers show good agreement with a laboratory FTIR spectrometer.