Flash photography was used to study the effects of absorption coefficient and fiber configurations on the bubble dynamics during pulsed-dye laser ablation of a thrombus model. The thrombus was modeled by unbounded 3.5% gelatin (Sigma, 175 Bloom) targets containing an absorbing dye (direct red, Sigma) submerged in water. Laser pulses (486 nm, 2 μs) of 100 mJ energy were delivered with solid and fluid core fibers. The laser induced bubbles were photographed from 10 μs to 1ms after the laser pulse using a 1 μs flash strobe. Bubble dimensions were measured as a function of time for different absorption coefficients and fiber configurations.
Each bubble was a single event and quite reproducible. Bubbles collapsed 400 μs to 700 μs after the laser pulse. The collapse time was much shorter than the growth time. When the fiber face was 1 mm from the target material, removal began at about 50 μs after the bubble had completely collapsed. Bubble wall velocities of the order of 40 m/s were recorded at collapse. Maximum bubble sizes and lifetimes were observed at an absorption coefficient of 300/cm. At a fiber-target distance of 2 mm, larger bubbles with longer lifetimes were produced. Bubbles created using a fluid core catheter were smaller than those produced with a solid core catheter.