Abstract
Raman sensing and microscopy are among the most specific optical technologies to identify the chemical compounds of unknown samples, and to enable label-free biomedical imaging. Here we present a method for stimulated Raman scattering spectroscopy and imaging with a time-encoded (TICO) Raman concept. We use continuous wave, rapidly wavelength-swept probe lasers and combine them with a short-duty-cycle actively modulated pump laser. Hence, we achieve high stimulated Raman gain signal levels, while still benefitting from the narrow linewidth and low noise of continuous wave operation. Our all-fibre TICO-Raman setup uses a Fourier domain mode-locked laser source to achieve a unique combination of high speed, broad spectral coverage (750–3,150 cm−1) and high resolution (0.5 cm−1). The Raman information is directly encoded and acquired in time. We demonstrate quantitative chemical analysis of a solvent mixture and hyperspectral Raman microscopy with molecular contrast of plant cells.
Highlights
Raman sensing and microscopy are among the most specific optical technologies to identify the chemical compounds of unknown samples, and to enable label-free biomedical imaging
We show the acquisition of high-resolution stimulated Raman scattering (SRS) spectroscopy and hyperspectral Raman microscopy with this TICO-Raman system
The intensity of the probe laser at that specific spectral position gets increased by stimulated Raman gain (SRG)
Summary
Raman sensing and microscopy are among the most specific optical technologies to identify the chemical compounds of unknown samples, and to enable label-free biomedical imaging. We achieve high stimulated Raman gain signal levels, while still benefitting from the narrow linewidth and low noise of continuous wave operation. Raman spectroscopy is an optical technology directly sensitive to molecular vibrations It can provide a wealth of information about the chemical composition of a sample. In biomedical applications, it enables label-free molecular imaging in vivo. With coherent anti-stokes Raman scattering (CARS), high signal-to-noise ratios have been achieved[6] and hyperspectral microscopy using a pulsed, stepwise wavelength-tuned laser has been demonstrated[7]. The demand for a flexible, broadband, high-resolution Raman imaging system based on fibre light sources is still unmet[21]
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