Some applications of ultrashort laser pulses in biology and medicine

Ultrashort laser pulses are finding increasing applications in biology and medicine. Such pulses can be used directly or after non-linear modification. Direct utilization includes propagation studies in scattering media with applications in optical mammography, dosimetry for photodynamic therapy and species concentration assessment. Intense continua of electromagnetic radiation of very brief duration are formed in the interaction of focused ultrashort and intense laser pulses with matter. Two different kinds of experiment using such radiation are described, employing visible radiation and x-rays, respectively. Focusing into water leads to the generation of a light continuum through self-phase modulation. The propagation of the light through tissue was studied, addressing questions related to specific tissue chromophore absorption. When terawatt laser pulses are focused onto a solid target with high nuclear charge Z, intense x-ray radiation of few ps duration and with energies exceeding hundreds of keV is emitted. Biomedical applications of this radiation are described, including differential absorption and gated-viewing imaging