Gain-switched Ti:sapphire laser-based photoacoustic imaging.

We demonstrate photoacoustic (PA) imaging using a compact gain-switched Ti:sapphire laser. Additionally, a simple laser configuration is provided. The Ti:sapphire laser is pumped using a frequency-doubled pulsed neodymium-doped yttrium aluminum garnet pulse laser operating at a repetition rate of 10 Hz, with a pump energy of 37 mJ. No water cooling is required for the Ti:sapphire crystal. The output pulse energy and pulse duration of the laser are 13.6 mJ and 11 ns, respectively. Thus, the power conversion efficiency is 36.7%. As the end mirror in a laser cavity is adjusted in a horizontal direction, the output wavelength can be tuned within a range of 725-880 nm with a spectral bandwidth of approximately 1 nm. The laser has a small footprint size of 50 cm×35 cm including even laser pumping. Because the near-infrared region has significant advantages in the context of absorption and scattering in biological tissues, our laser can be used for PA imaging. Apart from obtaining PA images of a tube filled with indocyanine green immersed in water and placed under chicken breast tissue, our laser system could also be used for the simultaneous PA and ultrasound (US) dual-modality imaging of blood vessels lying beneath the skin of a human middle finger. We used a commercially available US machine for the PA and US dual-modality imaging.