Two ‐frequency CARS imaging by switching fiber laser excitation

We describe a method for switching between two vibrational frequencies based on a single fiber‐laser source. Stokes pulses were generated by soliton self‐frequency shifting in a photonic crystal fiber. Pump and Stokes pulses were stretched to enhance vibrational resolution by spectral focusing. Stokes pulses were switched between two wavelengths on the millisecond time scale by a liquid‐crystal retarder. Proof‐of‐principle is demonstrated by coherent anti‐Stokes Raman imaging of polystyrene beads embedded in a poly(methyl methacrylate) (PMMA) matrix. The Stokes shift was switched between 3,050 cm−1, where polystyrene has a Raman transition, and 2,950 cm−1, where both polystyrene and PMMA have Raman resonances. The method can be extended to multiple vibrational modes. A CARS fiber‐laser excitation source allows Stokes wavelength switching at each pixel by soliton frequency shifting in a photonic crystal fiber. Dual images at 2,950 cm−1 and 3,050 cm−1 for polystyrene beads in a PMMA matrix demonstrate the method.
Source: Microscopy Research and Technique - Category: Laboratory Medicine Authors: Tags: MRT LETTER Source Type: research