The threshold fluences for gelatin containing an absorbing dye (10-2000 cm−1) under water were measured. Gelatin samples were prepared in a beaker to form a 1 cm thick layer and covered with water. The beaker was placed on a PVDF transducer. The light source was a one microsecond pulsed-dye laser Laser pulses were delivered via 300, 600, and 1000 micron fibers at a distance of 1 mm from the gelatin surface. The threshold energy was the minimum energy needed to produce an acoustic sgnal. These results were validated using spectrophotometric mass removal measurements. Microsecond non-contact ablation thresholds for artery and thrombus under water closely corresponded to those measured for gelatin targets with the same absorption coefficients. Conclusion: Threshold fluence is inversely proportional to the two-thirds root of the absorption coefficient and is relatively independent of material and geometry.