Pulse-length dependence of cellular response to intense near-infrared laser pulses in multiphoton microscopes

Abstract

The influence of the pulse length, tau , 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-micros 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 P(2)/tau dependence (P , 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.

Fast 100-nm resolution three-dimensional microscope reveals structural plasticity of mitochondria in live yeast

“…The average power of 1-2 mW of a 4Pi spot leads to a focal peak intensity of Ϸ80 GW͞cm 2 , which does not surpass the Ϸ200 GW͞cm 2 considered as an upper limit in nonlinear microscopy using Ϸ200-fs pulses (17). As a mode-locked Ti:Sapphire laser emits 1-2 W of average power, a parallelization by 1,000 foci rather than by n ϭ 16-64 appears possible.…”

Two-color two-photon excitation of indole using a femtosecond laser regenerative amplifier

“…When using a femtosecond amplifier for the two-photon imaging applications, photodamage is an important issue that should be addressed. In the early multiphoton imaging researches by using oscillator, about a few mW output power corresponding peak power of nJ level is employed to image tissue due to the concern on peak power damage [34,35]. In those cases, the samples are quite transparent and optically homogeneous.…”

Principles of nonlinear microscopy and application possibilities in dermatology

“…Elsôként tehát a külön-bözô károsító tényezôk detektálására fókuszáltunk. Lézerrel történô munka során a DNS három fotonos abszorpciója kö-vetkeztében, az UVB sugárzás által okozott károsodásokhoz hasonlóan, ciklobután pirimidin dimerek képzôdhetnek, melyek elégtelen reparáció esetén kiinduló elemei lehetnek egy esetleges mutációnak a hámsejtekben (42). A ciklobután pirimidin dimereket immunfluoreszcens jelölési technikával azonosítottuk, így meg tudtuk állapítani, hogy melyek azok a lézer paraméterek, melyekkel jó minôségû felvételeket lehet készíteni, de nem okozunk károsodást a sejtekben (43).…”