A mid-IR photothermal imaging system is presented that features an integrated ultrafast erbium-doped fiber probe laser
for the first time. With a mid-IR tunable quantum cascade laser (QCL) as the pump laser, vibrational molecular modes
are excited and the thermally-induced changes in the refractive index are measured with a probe laser. The custom-built,
all-fiber ultrafast probe laser at telecommunication wavelengths is compact, robust and thus an attractive source
compared to bulky and alignment sensitive Ti:sapphire probe lasers. We present photothermal spectra and images with
good contrast for a liquid crystal sample, demonstrating highly sensitive, label-free photothermal microscopy with a
mode-locked fiber probe laser.