2D plasmons are of particular interest in the exploration of light–matter interactions in 2D materials. In 2D plasmonic materials, response time (in sub‐picosecond scale) of free carriers is order of magnitude faster than excitonic recombination in semiconductors, making them highly attractive for realizing faster optical switching and modulation in nanoscale devices. However, the small carrier density in gapless 2D plasmonic materials like graphene has strongly limited the strength of light–matter interaction and the operative spectral range. Here, it is shown that in optically activated plasmonic molybdenum oxide (MoO3) sheets of atomic thickness, the nonlinear optical (NLO) absorption, characterized by a saturable behavior in the near‐infrared region, is notably enhanced by the plasmon resonance, giving a modulation depth of 34.96%. Ultrafast pump‐probe spectroscopy reveals that the transient photobleaching in plasmonic MoO3 nanosheets associated with the relaxation of hot electrons recovers in a timescale less than 200 femtoseconds (fs). This ultrafast NLO response allows the development of an optical switch based on saturable absorption that enables the generation of mode‐locked laser pulses from a fiber laser operating at 1.0 µm region. The results may have strong implications for the application of 2D plasmonics based on 2D MoO3 in nanophotonics.
A three-dimensional (3D) photonic nanojet (PNJ) emerging from a liquid-immersed core–shell dielectric microsphere is numerically investigated by the finite-difference time-domain (FDTD) method. An ultra-elongated PNJ with an effective length larger than 57 wavelengths while retaining a high intensity and a large working distance is obtained from the simulation. In particular, PNJ properties, including intensity enhancement, working distance, effective length, and full width at half maximum (FWHM), can be well tuned and controlled by varying the refractive index of the immersed liquid. We believe that this design is applicable to many fields, such as material science, nanophotonics, and biomedicine.
We report a high average power mid-infrared picosecond (ps) pulse bunch output by means of direct difference frequency generation (DFG) in periodically poled magnesium-doped lithium niobate between a linearly polarized ps pulse bunch Yb fiber laser and a synchronized Er fiber laser. The ps pulse bunch Yb fiber laser was composed of an all polarization maintained “figure of eight” structured mode-locked Yb fiber laser as the seed, a pulse multiplier, and two stages of Yb fiber amplifiers. The mode-locked Yb fiber laser has an output ps laser pulse at 1030 nm with a repetition rate of 16.32 MHz. The pulses were then transformed to the pulse bunches through the pulse multiplier. Within each bunch, there were 16 equally spaced pulses with pulse widths of 8.5 ps and time intervals around 300 ps. The Er fiber laser had a gain switched seed laser diode working at 1550 nm with a pulse width around 5.1 ns, which was synchronized to the mode-locked Yb fiber laser pulse bunch, and two stages of Er fiber amplifiers. Under the average power of 27.8 W of Yb fiber laser, we obtained an average output power of 3.1 W at 3.07 µm. This is, to the best of our knowledge, the highest average power mid-infrared ps pulse bunch obtained via DFG directly.
We have demonstrated a Yb-doped fiber laser (YDFL) based on a multifunctional acousto-optic tunable filter (AOTF) with flexible wavelength generation capability. The number of channels, as well as their diffracted wavelengths and corresponding peak transmittances of the AOTF, can be widely tuned by changing the composite drive signal from a homemade arbitrary wave generation (AWG) board enabling single-/multi-wavelength lasing with different central wavelengths and relative intensities. The maximal wavelength tuning range and minimal resolved wavelength spacing are
∼
80
n
m
and
∼
1.5
n
m
, respectively, with 3 dB bandwidth less than 0.15 nm for each laser line, showing great potential for further nonlinear frequency conversion. To the best of our knowledge, this is the first demonstration of flexible wavelength generation from a multifunctional AOTF-based YDFL directly driven by an AWG board.
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