Laser induced microexplosions: Ultrafast physics with clinical applications

Presentation Date: 

Monday, May 22, 2000


Chemical Center Seminar, Lund University (Lund, Sweden)

Presentation Slides: 

Recently there has been much interest in using femtosecond laser pulses in surgical applications. For example, femtosecond lasers could replace the nanosecond systems currently used for opthalmic photodisruption, providing improved surgical precision and adding versatility. In surgical applications, it is the high intensity of femtosecond laser pulses that is exploited. By tightly focusing these short pulses, the intensity becomes high enough to cause nonlinear absorption inside a transparent material (such as the vitreous humor). The absorption produces a hot plasma inside the sample that is highly localized near the laser focus. This plasma rapidly expands into the surrounding volume, producing a microscopic explosion - a microexplosion. For surgical applications, the plasma provides a scalpel, while the nature and extent of the expansion determine the precision of the ""blade.""

In this talk we will discuss the production and dynamics of microexplosions in transparent materials, focusing, in particular, on water as the transparent medium. Using pump-probe techniques, we measured the initial expansion of the plasma with unprecedented temporal resolution. We find that the initial expansion velocity reaches 90 km/s, the fastest expansion of a solid density material observed to date. Furthermore, we have followed the dynamics of a microexplosion from these initial stages to the collapse of the bubble. We will discuss the importance of certain features of these dynamics for surgical applications. We will also describe some acoustic measurements that indicate femtosecond pulses offer advantages over longer pulses for surgical applications. In particular, we find that femtosecond pulses produce more consistent breakdown at a lower energy compared to picosecond pulses. Finally we will discuss some preliminary investigations we made into using femtosecond laser induced microexplosions to cut beneath the surface of skin tissue.