2,762 research outputs found
On-chip electro-optic tuning of a lithium niobate microresonator with integrated in-plane microelectrodes
We demonstrate electro-optic tuning of an on-chip lithium niobate
microresonator with integrated in-plane microelectrodes. First two metallic
microelectrodes on the substrate were formed via femtosecond laser process.
Then a high-Q lithium niobate microresonator located between the
microelectrodes was fabricated by femtosecond laser direct writing accompanied
by focused ion beam milling. Due to the efficient structure designing, high
electro-optical tuning coefficient of 3.41 pm/V was observed.Comment: 6 pages, 3 figure
Terahertz imaging with sub-wavelength resolution by femtosecond laser filament in air
Terahertz (THz) imaging provides cutting edge technique in biology, medical
sciences and non-destructive evaluation. However, due to the long wavelength of
the THz wave, the obtained resolution of THz imaging is normally a few hundred
microns and is much lower than that of the traditional optical imaging. We
introduce a sub-wavelength resolution THz imaging technique which uses the THz
radiation generated by a femtosecond laser filament in air as the probe. This
method is based on the fact that the femtosecond laser filament forms a
waveguide for the THz wave in air. The diameter of the THz beam, which
propagates inside the filament, varies from 20 {\mu}m to 50 {\mu}m, which is
significantly smaller than the wavelength of the THz wave. Using this highly
spatially confined THz beam as the probe, THz imaging with resolution as high
as 20 {\mu}m (~{\lambda}/38) can be realized.Comment: 10 pages, 7 figure
Terahertz Wave Guiding by Femtosecond Laser Filament in Air
Femtosecond laser filament generates strong terahertz (THz) pulse in air. In
this paper, THz pulse waveform generated by femtosecond laser filament has been
experimentally investigated as a function of the length of the filament.
Superluminal propagation of THz pulse has been uncovered, indicating that the
filament creates a THz waveguide in air. Numerical simulation has confirmed
that the waveguide is formed because of the radially non-uniform refractive
index distribution inside the filament. The underlying physical mechanisms and
the control techniques of this type THz pulse generation method might be
revisited based on our findings. It might also potentially open a new approach
for long-distance propagation of THz wave in air.Comment: 5 pages, 6 figure
Fabrication of three-dimensional microdisk resonators in calcium fluoride by femtosecond laser micromachining
We report on fabrication of on-chip calcium fluoride (CaF2) microdisk
resonators using water-assisted femtosecond laser micromachining. Focused ion
beam (FIB) milling is used to create ultra-smooth sidewalls. The quality
(Q)-factors of the fabricated microresonators are measured to be 4.2x10^4 at
wavelengths near 1550 nm. The Q factor is mainly limited by the scattering from
the bottom surface of the disk whose roughness remains high due to the
femtosecond laser micromachining process. This technique facilitates formation
of on-chip microresonators on various kinds of bulk crystalline materials,
which can benefit a wide range of applications such as nonlinear optics,
quantum optics, and chip-level integration of photonic devices.Comment: 7 pages, 3 figure
Short-term anti-vascular endothelial growth factor treatment elicits vasculogenic mimicry formation of tumors to accelerate metastasis
Impulsive rotational Raman scattering of N2 by a remote "air laser" in femtosecond laser filament
We report on experimental realization of impulsive rotational Raman
scattering from neutral nitrogen molecules in a femtosecond laser filament
using an intense self-induced white-light seeding "air laser" generated during
the filamentation of an 800 nm Ti: Sapphire laser in nitrogen gas. The
impulsive rotational Raman fingerprint signals are observed with a maximum
conversion efficiency of ~0.8%. Our observation provides a promising way of
remote identification and location of chemical species in atmosphere by
rotational Raman scattering of molecules.Comment: 4 pages, 4 figure
High-brightness switchable multi-wavelength remote laser in air
Remote laser in air based on amplified spontaneous emission (ASE) has
produced rather well-collimated coherent beams in both backward and forward
propagation directions, opening up possibilities for new remote sensing
approaches. The remote ASE-based lasers were shown to enable operation either
at ~391 and 337 nm using molecular nitrogen or at ~845 nm using molecular
oxygen as gain medium, depending on the employed pump lasers. To date, a
multi-wavelength laser in air that allows for dynamically switching the
operating wavelength has not yet been achieved, although this type of laser is
certainly of high importance for detecting multiple hazard gases. In this
Letter, we demonstrate, for the first time to our knowledge, a harmonic-seeded
switchable multi-wavelength laser in air driven by intense mid-infrared
femtosecond laser pulses. Furthermore, population inversion in the
multi-wavelength remote laser occurs at an ultrafast time-scale (i.e., less
than ~200 fs) owing to direct formation of excited molecular nitrogen ions by
strong-field ionization of inner-valence electrons, which is fundamentally
different from the previously reported pumping mechanisms based either on
electron recombination of ionized molecular nitrogen or on resonant two-photon
excitation of atomic oxygen fragments resulting from resonant two-photon
dissociation of molecular oxygen. The bright multi-wavelength laser in air
opens the perspective for remote detection of multiple pollutants based on
nonlinear spectroscopy.Comment: 18 pages, 5 figure
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