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Picosecond pulsed two‐photon imaging with repetition rates of 200 and 400 MHz
Author(s) -
Jörg Bewersdorf,
Stefan W. Hell
Publication year - 1998
Publication title -
journal of microscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.569
H-Index - 111
eISSN - 1365-2818
pISSN - 0022-2720
DOI - 10.1046/j.1365-2818.1998.00379.x
Subject(s) - picosecond , femtosecond , optics , materials science , laser , wavelength , numerical aperture , pulse duration , sapphire , excitation , pulse (music) , two photon excitation microscopy , microscope , optoelectronics , fluorescence , physics , detector , quantum mechanics
We show the viability of high‐resolution two‐photon fluorescence imaging of fixed and live cells by exciting the fluorophores with a train of near‐infrared pulses with duration in the picosecond range. This is exemplified with a compact, diode‐pumped Nd:YVO 4 laser, emitting trains of 7‐ps pulses at a wavelength of 1064 nm, with a repetition rate of 200 MHz at two separate outputs. Incoherent combination of the outputs enabled two‐photon excitation with a repetition rate of 400 MHz. For a numerical aperture of 1.4 (oil), we used an average illumination power of up to 20–40 mW at the sample. The pulses were coupled into a beam scanning microscope, either directly or through a single mode glass fibre. Compared with standard femtosecond titanium–sapphire excitation conditions, our experiments were performed with a 2.5 or 5 times higher repetition rate, 30–70 times longer pulses and 10–35 times lower pulse peak intensity. The experiments indicate the possibility of significantly relaxing the temporal pulse width constraints for a series of applications.