Label-free CARS microscopy through a multimode fiber endoscope

Area of Science:

• Biomedical Optics
• Microscopy
• Spectroscopy

Background:

• Multimode fibers are emerging as ultra-thin endoscopes for in vivo imaging.
• Label-free microscopy offers chemical contrast without exogenous agents.

Purpose of the Study:

• To extend multimode fiber endoscopy to label-free nonlinear microscopy.
• To achieve chemical contrast imaging using coherent anti-Stokes Raman scattering (CARS) through a multimode fiber endoscope.
• To explore applications in in situ diagnosis of potentially malignant tissue.

Main Methods:

• Utilized a commercial 125 µm diameter, 0.29 NA GRIN fiber.
• Employed wavefront shaping with a spatial light modulator (SLM) to create scanned foci.
• Implemented CARS microscopy through the multimode fiber for chemical imaging.
• Utilized epi-detection for signal collection.

Main Results:

• Demonstrated label-free chemical contrast imaging via CARS through a multimode fiber endoscope.
• Achieved rapid per-pixel integration times as low as 1 ms.
• Successfully imaged 2 µm polystyrene and 2.5 µm PMMA beads, showcasing chemical selectivity.

Conclusions:

• Multimode fiber CARS endoscopy provides a new platform for label-free chemical imaging in vivo.
• This technique holds promise for instant and in situ diagnosis of biological tissues.
• The developed method opens new avenues for advanced endoscopic diagnostics.