Modeling of pressure generation by lasers in melanosomes: how to avoid stress confinement and blow up a melanosome

摘要

Abstract: We have made a detailed theoretical investigation of the pressure generated in melanosomes upon absorption of laser energy. Our model treats the melanosome as a homogeneous absorber surrounded by a transparent water medium. The mechanical impedance mismatch between the absorbing melanosome and the surrounding medium is taken into account and has important ramifications. We have calculated the pressure profiles for pulses of microsecond duration down to picosecond duration. We show that the concept of stress confinement is not valid for this system. Though pressure amplitudes generated at the surface do reach a limit as the pulse duration is shortened below a nanosecond, no such pressure confinement occurs at the center of the absorber. As the pulse duration is shortened below a nanosecond, the tensile pressure at the center continues to rise without limit. This implies that explosive fracturing of the melanosome can occur due to the large tensile stresses, and accomplishing this fracturing requires smaller fluences as the pulse duration is shortened. We present quantitative results exhibiting how the core's tensile stress increases as the pulse duration is shortened. !9