The stand-off, range-resolved detection of hydrogen production rates is a valuable mechanism for the long-term condition monitoring of packages containing intermediate-level nuclear materials. To exploit this effect we have developed a long-range optical sensor system which uses Raman detection of hydrogen. Our need for operation over extended ranges (up to 100m) results in very low Raman signals. We therefore use time-correlated (with respect to the outgoing excitation laser pulse) and spectrally-resolved single-photon detection to ascertain molecular species, position and concentration as revealed by photon energy, arrival time and number, respectively.
We report on multiphoton imaging of biological samples performed with continuum infrared source generated
in photonic crystal fibers (PCFs). We studied the spectra generated in PCFs with dispersion profiles designed
to maximize the power density in the 700-1000 nm region, where the two-photon absorption cross sections of
the most common dyes lie. Pumping in normal dispersion region, with <140 femtosecond pulses delivered by a
tunable Ti:Sa laser (Chameleon Ultra II by Coherent Inc.), results in a limitation of nonlinear broadening up to a
mean power density above 2 mW/nm. Axial and lateral resolution obtained with a scanning multiphoton system
has been measureed to be near the theoretical limit. The possibility of simultaneous two-photon excitation of
different dyes in the same sample and high image resolution are demonstrated at tens of microns in depth.
Signal-to-noise ratio and general performances are found to be comparable with those of a single wavelength
system, used for comparison.
We describe the realization and characterization of a broadband, high power density and fully spectrally controllable
source, suitable for multiphoton imaging of biological samples. We used a photonic crystal fiber (PCF)
with selected dispersive and non-linear properties, in order to generate, when pumped with <140 femtosecond
pulses delivered by a tunable Ti:Sa laser (Chameleon Ultra II by Coherent Inc.), a smooth continuum in the
700nm-950nm region, with average power density grater than 2mW/nm. Time distribution of the generated
spectrum has been measured with autocorrelation technique. Axial and lateral resolution obtained with a scanning
multiphoton system has been determined to be near the theoretical limit. The possibility of two-photon
excitation of different dyes in the same sample and high image resolution are demonstrated at tens of microns
in depth. Future developments and different applications are also discussed.
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