Custom designed acoustic pulses

We have used a tunable, infrared, free-electron laser with a Pockels cell c ontrolled pulse duration to generate photoacoustic pulses with separate var iable rise times (from 15 to 100 ns), durations (100-400 ns), and amplitude s (0.005-0.1 M.Pa). The tunability of the free-electron laser across water absorption bands allows the rise time of the thermal-elastically generated acoustical pulsed to be varied, while a Pockels cell controls the duration and cross polarizers control the pressure amplitude. The mechanical effects of pressure transients on biological tissue can have dramatic consequences . In addition to cell necrosis, carefully controled pressure transients can also be used for therapeutic applications, such as drug delivery and gene therapy; This technique permits systemic probing of how biological tissue i s affected by stress transients. (C) 1999 Society of Photo-Optical Instrume ntation Engineers. [S1083-3668(99)00302-0].