  Frequency modulation coherent anti-Stokes Raman scattering (FM CARS) is
presented, using a compact as well as fast and widely tunable fiber-based light
source. With this light source Raman resonances between 700 cm$^{-1}$ and 3200
cm$^{-1}$ can be addressed via wavelength tuning within only 5 ms, which allows
for FM CARS measurements with frame-to-frame wavelength switching. Moreover,
the functionality for high-sensitivity FM CARS measurements was integrated by
means of fiber optics to keep a stable and reliable operation. The light source
accomplished FM CARS measurements with a 40 times enhanced sensitivity at a
lock-in amplifier (LIA) bandwidth of 1 Hz. For fast imaging with frame-to-frame
wavelength switching at a LIA bandwidth of 1 MHz a 18-fold contrast enhancement
could be verified, making this light source ideal for routine and out-of-lab FM
CARS measurements for medical diagnostics or environmental sensing.
