Ultrafast imaging Raman spectroscopy of large-area samples without stepwise scanning

Abstract

Abstract.Step-by-step, time-consuming scanning of the sample is still the state-of-the-art in imaging Raman spectroscopy. Even for a few 100 image points the measurement time may add up to minutes or hours. A radical decrease in measurement time can be achieved by applying multiplex spectrographs coupled to imaging fiber bundles that are successfully used in astronomy. For optimal use of the scarce and expensive observation time at astronomical observatories, special high-performance spectrograph systems were developed. They are designed for recording thousands of spatially resolved spectra of a two-dimensional image field within one single exposure. Transferring this technology to imaging Raman spectroscopy allows a considerably faster acquisition of chemical maps. Currently, an imaging field of up to 1 cm 2 can be investigated. For porcine skin the required measurement time is less than 1 min. For this reason, this technique is of particular interest for medical diagnostics, e.g., the identification of potentially cancerous abnormalities of skin tissue.

Label‐Free Molecular Imaging of Biological Cells and Tissues by Linear and Nonlinear Raman Spectroscopic Approaches

“…Images can be registered by sequential acquisition of spectra and moving the Angewandte Chemie Reviews sample or the probe.T his procedure is time-consuming because the exposure time for each spectrum lies in the range of seconds,a nd the acquisition of hundreds of spectra takes several minutes.This is impractical in clinical settings.A technique was presented that allows for capturing an entire Raman image with only one exposure without the need for ascanning procedure. [280] Another challenge for fiber-optic Raman spectroscopy in clinical settings is that the ambient light needs to be turned off to avoid overlapping signals from external light sources.T he influence of ambient light was studied in the context of fiberoptic Raman spectroscopy of the skin. At the end of the bundle,the 400 fiber cores were arranged in one row to form apseudo-slit for the spectrograph.…”

“…Another version was described with microlenses,which offers alarger field of view (1 cm 2 )w ithout microscope coupling. [280] Another challenge for fiber-optic Raman spectroscopy in clinical settings is that the ambient light needs to be turned off to avoid overlapping signals from external light sources.T he influence of ambient light was studied in the context of fiberoptic Raman spectroscopy of the skin. [281] To overcome the problems associated with external light sources,s hiftedexcitation or modulated-excitation Raman scattering was combined with fiber-optic probes.…”

Nonscanning large-area Raman imaging for ex vivo/in vivo skin cancer discrimination

“…Figure 15 left shows the top of the image acquisition head with a skin sample and the upper MLA underneath. A detailed description of the Raman acquisition optics was given previously [18]. In brief: For excitation, a 784.5 nm diode laser with a tunable output power up to 500 mW was used.…”

Improving the frame rates of Raman image sequences recorded with integral field spectroscopy using windowing and binning methods

“…As a result IFS is particularly attractive for generating time‐lapse Raman images (TLRI) with unprecedented high frame rates. The potential of this concept was previously reported by tracking the sucrose Raman signal of a dissolving piece of sugar in water over time . This approach is particularly promising for monitoring spatial Raman features of (bio­)chemical reactions in real time.…”

“…The potential of this concept was previously reported by tracking the sucrose Raman signal of a dissolving piece of sugar in water over time. [4] This approach is particularly promising for monitoring spatial Raman features of (bio)chemical reactions in real time. However, the frame rate is heavily restricted by the long readout times of the large area charge coupled device (CCD) detectors required to record a large number of spectra along with broad wavelength coverage.…”