Stimulated Raman scattering (SRS) microscopy is a labelfree chemical imaging technique. Two-color imaging is often necessary to determine the distribution of chemical species in SRS microscopy. Current multi-color SRS imaging methods involve complicated instrumentation or longer data acquisition time or are limited to transmission imaging. In this Letter, we show that by adding a simple fiber amplifier to a 2 ps laser source and optical-parametric-oscillatorbased SRS setup, one can achieve

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... taneous two-color or frequency modulation SRS microscopy. The fiber amplifier can generate a wavelength tunable laser of 10 nm around the Stokes laser wavelength at 1031 nm with average power greater than 200 mW. In vivo and ex vivo lipid-protein imaging of mouse brain and skin is demonstrated. To further demonstrate the potential of this technique in high-speed in vivo imaging, white blood cells in a blood stream are imaged in a live mouse. OCIS codes: (170.3880) Medical and biological imaging; (180.4315) Nonlinear microscopy; (110.4234) Multispectral and hyperspectral imaging; (060.2320) Fiber optics amplifiers and oscillators; (180.5655) Raman microscopy.