Vibrational Photoacoustic Tomography: Chemical Imaging beyond the Ballistic Regime

Proof-of-concept of vibrational photoacoustic tomography is demonstrated with a home-built Raman laser generating greater than 100 mJ of energy per pulse at a 1197 nm wavelength. We employed this system for excitation of the second overtone transition of C-H bonds. The vibrational photoacoustic signal from a C-H-rich polyethylene tube phantom placed under 3 cm thick chicken breast tissue was obtained with a signal-to-noise ratio of 2.5. Further, we recorded a photoacoustic image of a polyethylene ring placed under 5 mm chicken tissue with excellent contrast. This development opens new opportunities of performing label-free vibrational imaging in the deep tissue regime.