CELLULAR-RESPONSE TO NEAR-INFRARED FEMTOSECOND LASER-PULSES IN 2-PHOTON MICROSCOPES

The influence of femtosecond near-infrared (NIR) microirradiation on c ell vitality and cellular reproduction has been studied. Chinese hamst er ovary cells exposed to a highly focused 150-fs scanning beam at 730 , 760, and 800 nm (80 MHz, 80-mu s pixel dwell time) of less than or e qual to 1 mW remained unaffected by the femtosecond microbeam. However , increased mean power led to impaired cell division. At greater than or equal to 6-mW mean power, cells were unable to form clones. They di ed or became giant cells. Complete cell destruction, including cell fr agmentation, occurred at mean powers >10 mW. Cell death was accompanie d by intense luminescence in the mitochondrial region. When we conside r the diffraction-limited spot size in the submicrometer region, inten sities and photon flux densities of 0.8-kW pulses (10-mW mean power) a re of the order of terawatts per square centimeter (10(12) W/cm(2)) an d 10(32) photons cm(-2)s(-1), respectively. Extremely high fields may induce destructive intracellular plasma formation. The power limitatio ns should be considered during NIR femtosecond microscopy of vital cel ls and in the design of compact NIR femtosecond solid-state lasers for two-photon microscopes. (C) 1997 Optical Society of America