Uses of ultrashort pulses and measurement techniques in laser medicine

Abstract

Recent developments in the generation of ultrashort laser pulses, including advances in picosecond and femtosecond laser generation and measurement techniques, permit the investigation of a wide variety of laser medical phenomena. Ultrashort pulse durations allow not only the measurement of transient phenomena but also enable the investigation of laser tissue interaction at extremely high peak laser intensities. We describe studies of laser tissue interaction using high-intensity femtosecond laser pulses. Studies of femtosecond laser injury in the rabbit retina are discussed. The retina provides a well-studied model system for the investigation of laser tissue effects. In contrast to longer pulse durations, the femtosecond pulses permit the investigation of tissue effects at intensities in excess of 1011 W/cm2 with reduced thermal or acoustic effects. Injury thresholds and mechanisms are discussed. As an example of nonlinear laser tissue interaction, we describe the use of high-intensity femtosecond pulses for producing ablation of the cornea. These results demonstrate ablation in a system which is nominally transparent to the laser wavelength. In addition, we discuss applications of time-resolved measurement techniques for the investigation of laser medical and laser tissue interaction. As an example, we describe optical ranging using femtosecond pulses. This technique has been demonstrated for measuring the epidermal structure of human skin as well as the anterior eye and corneal profile alterations produced by laser ablation. Finally, the use of time-resolved spectroscopic measurement techniques and applications to the measurement of transient excited state dynamics and photophysical processes are discussed.