Kavli Affiliate: Frank Wise
| First 5 Authors: Yishai Eisenberg, Wenchao Wang, Shitong Zhao, Eric S. Hebert, Yi-Hao Chen
| Summary:
An exciting recent development for deep-tissue imaging with cellular
resolution is three-photon fluorescence microscopy (3PM) with excitation at
long wavelengths (1300 and 1700 nm). In the last few years, long-wavelength 3PM
has driven rapid progress in deep-tissue imaging beyond the depth limit of
two-photon microscopy, with impacts in neuroscience, immunology, and cancer
biology. However, wide adoption of 3PM faces challenges. Three-photon
excitation (3PE) is naturally weaker than two-photon excitation, which places a
premium on ultrashort pulses with high peak power. The inefficiency,
complexity, and cost of current sources of these pulses present major barriers
to the use of 3PM in typical biomedical research labs. Here, we describe a
fiber-based source of femtosecond pulses with multi-megawatt peak power,
tunable from 850 nm to 1700 nm. Compressed pulses from a fiber amplifier at
1030~nm are launched into an antiresonant hollow-core fiber filled with argon.
By varying only the gas pressure, pulses with hundreds of nanojoules of energy
and sub-100 fs duration are obtained at wavelengths between 850 and 1700 nm.
This approach is a new route to an efficient, robust, and potentially low-cost
source for multiphoton deep-tissue imaging. In particular, 960-nJ and 50-fs
pulses are generated at 1300 nm with a conversion efficiency of 10%. The
nearly 20-MW peak power is an order of magnitude higher than the previous best
from femtosecond fiber source at 1300~nm. As an example of the capabilities of
the source, these pulses are used to image structure and neuronal activity in
mouse brain as deep as 1.1 mm below the dura.
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