Mid-IR Photothermal Imaging with a Compact Ultrafast Fiber Probe Laser

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.