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.
The layered anisotropic chalcogenide semiconductors GaSe and GaTe single crystals have been grown by a modified
vertical Bridgman technique using high purity Ga (7N) and in-house zone refined (ZR) precursor materials (Se and Te).
The crystals harvested from ingots of up to 10 cm length and up to 2" diameter, have been characterized by measuring
resistivity through current-voltage (I-V) characteristics and bulk carrier concentration and mobility through Hall effect
measurements. Micro-hardness, infrared microscopy, etching characteristics, low-temperature photoluminescence (PL)
and contact resistivity studies have also been performed to further characterize the grown crystals.