The influence of the pulse length, τ , of ultrashort laser pulses at 780 and 920 nm on cell vitality and cellular reproduction has been studied. A total of 2400 nonlabeled cells were exposed to a highly focused scanning beam from a mode-locked 80-MHz Ti:sapphire laser with 60-µs pixel dwell time. For the same pulse energy, destructive effects were more pronounced for shorter pulses. The damage behavior was found to follow approximately a <i>P</i><sup>2</sup>/τ dependence (<i>P</i> , mean power), indicating that cell destruction is likely based on a two-photon excitation process rather than a one- or a three-photon event. Therefore, femtosecond as well as picosecond pulses provide approximately the same relative optical window for safe two-photon fluorescence microscopy.
© 1999 Optical Society of America
(140.0140) Lasers and laser optics : Lasers and laser optics
(140.3070) Lasers and laser optics : Infrared and far-infrared lasers
(180.0180) Microscopy : Microscopy
(270.4180) Quantum optics : Multiphoton processes
(320.5550) Ultrafast optics : Pulses
K. König, T. W. Becker, P. Fischer, I. Riemann, and K.-J. Halbhuber, "Pulse-length dependence of cellular response to intense near-infrared laser pulses in multiphoton microscopes," Opt. Lett. 24, 113-115 (1999)