Laser tissue welding is a thermal process that causes binding of two tissue samples after irradiation by a laser pulse. The absorption of the laser energy is aided by the addition of a dye such as Indocyanine Green (ICG) on one tissue surface. ICG has an absorption peak at 774 nm when dissolved in water, thus making an 800 nm diode laser a suitable choice for welding. After successive laser pulses, the dye photobleaches from green to orange, altering the absorption characteristics of the dyed tissue. We measured the ICG deposition in aortic heterograft by analyzing the acoustic wave induced by irradiation of the dyed tissue by a Q-switched Nd-YAG laser. The Nd-YAG laser was coupled to an Optical Parametric Oscillator (OPO) for an output pulse of 800 nm and 4.75 ns. The dye deposition was analyzed for successive pulses of the diode laser until the dye was fully photobleached, indicated by an orange color. The absorption profiles obtained could be used for optimization of laser pulse parameters in laser tissue welding.