Coherent anti-Stokes Raman scattering (CARS) microscopy is a video rate, label-free biological imaging technique that can provide three dimensional sectioning of live tissue. Coherent anti-Stokes Raman scattering imaging is performed by probing the sample with two synchronized picosecond pulse trains, with the frequency difference between the colors tuned to a vibrational resonance of the sample. Its implementation in clinical settings has been limited by the expense and required maintenance of the solid-state source of the picosecond pulses. A source based on optical fiber could provide a robust and low cost alternative, allowing for broader application of Coherent anti-Stokes Raman scattering microscopy. Here we report on the development of a fiber optical parametric oscillator (OPO) for Raman microscopy. The optical parametric oscillator is pumped by an amplified ytterbium-doped fiber laser. The 1030 nm pump pules are converted to 800 nm through normal dispersion four wave mixing in a photonic crystal fiber, and those two wavelengths are used in imaging. High-quality images of mouse tissues produced by Coherent anti-Stokes Raman scattering microscopy with the fiber optical parametric oscillator are presented.
Figure Caption: Epi-CARS images of sebaceous gland in a mouse ear at the2850 cm−1 shift. Image size is 186×186 um.512 × 512 pixels with a 4 us per pixel dwell time, no averaging.
Opt Lett. 2013 ;38(20):4154-7.
Lamb ES(1), Lefrancois S (1), Ji M(2), Wadsworth WJ (3), Xie XS (2), Wise FW (1).
(1) School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14853, USA &
(2) Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA &
(3) Centre for Photonics and Photonic Materials, University of Bath, Bath, BA2 7AY, UK.
We present a synchronously pumped fiber optical parametric oscillator for coherent anti-Stokes Raman scattering microscopy. Pulses from a 1 um Yb-doped fiber laser are amplified and frequency converted to 779-808 nm through normal dispersion four-wave mixing in a photonic crystal fiber. The idler frequency is resonant in the oscillator cavity, and we find that bandpass filtering the feedback is essential for stable, narrow-bandwidth output. Experimental results agree quite well with numerical simulations of the device. Transform-limited 2 ps pulses with energy up to 4 nJ can be generated at the signal wavelength. The average power is 180 mW, and the relative-intensity noise is much lower than that of a similar parametric amplifier. High-quality coherent Raman images of mouse tissues recorded with this source are presented.