A series of layered molybdenum dichalcogenides,
i.e.
,MoX
2
(X
¼
S, Se
and Te), were prepared in cyclohexyl pyrrolidinone by a liquid-phase
exfoliation technique. The high quality of the two-dimensional
nanostructures was veri
fi
ed by transmission electron microscopy and
absorption spectroscopy. Open- and closed-aperture
Z
-scans were
employed to study the nonlinear absorption and nonlinear refraction
of the MoX
2
dispersions, respectively. All the three-layered nano-
structures exhibit prominent ultrafast saturable absorption (SA) for
both femtosecond (fs) and picosecond (ps) laser pulses over a broad
wavelength range from the visible to the near infrared. While the
dispersions treated with low-speed centrifugation (1500 rpm) have an
SA response, and the MoS
2
and MoSe
2
dispersions after higher speed
centrifugation (10 000 rpm) possess two-photon absorption for fs
pulses at 1030 nm, which is due to the signi
fi
cant reduction of the
average thickness of the nanosheets; hence, the broadening of band
gap. In addition, all dispersions show obvious nonlinear self-defo-
cusing for ps pulses at both 1064 nm and 532 nm, resulting from the
thermally-induced nonlinear refractive index. The versatile ultrafast
nonlinear properties imply a huge potential of the layered MoX
2
semiconductors in the development of nanophotonic devices, such as
mode-lockers, optical limiters, optical switches,
etc
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Jonathan Nesbit Coleman,
Jonathan Coleman,
Werner Blau