30 research outputs found
Efficient Generation of Intense Broadband Terahertz Pulses from Quartz
The intense terahertz (THz) pulses facilitate the observation of various
nonlinear optical effects and manipulation of material properties. In this
work, we report a convenient approach that can produce strong broadband
terahertz pulses with center frequency tunable between 2-4 THz. The coherent
THz light source with pulse energy of 1.2 microjoule can be generated from a
low-cost crystalline quartz pumped by an ultrashort tilted wave-front pulse.
Thanks to the wide transparent spectral window and high damage threshold, our
theoretical analysis and experiment show that the optical rectification in
quartz is as efficient as that in LiNbO3, but covers much broader spectral
range. This work not only provides the light source that is urgently needed for
nonlinear THz spectroscopy beyond 1 THz, but offers an alternative route in the
selection of nonlinear optical crystals for optical frequency conversion
Preventive Effect of Curcumin Against Chemotherapy-Induced Side-Effects
Cancer is still a severe threat to the health of people worldwide. Chemotherapy is one of main therapeutic approaches to combat cancer. However, chemotherapy only has a limited success with severe side effects, especially causing damage to normal tissues such as bone marrow, gastrointestine, heart, liver, renal, neuron, and auditory tissues, etc. The side-effects limit clinical outcome of chemotherapy and lower patients’ quality of life, and even make many patients discontinue the chemotherapy. Thus, there is a need to explore effective adjuvant strategies to prevent and reduce the chemotherapy-induced side effects. Naturally occurring products provide a rich source for exploring effective adjuvant agents to prevent and reduce the side effects in anticancer chemotherapy. Curcumin is an active compound from natural plant Curcuma longa L., which is widely used as a coloring and flavoring agent in food industry and a herbal medicine in Asian countries for thousands of years to treat vomiting, headache, diarrhea, etc. Modern pharmacological studies have revealed that curcumin has strong antioxidative, anti-microbial, anti-inflammatory and anticancer activities. Growing evidence shows that curcumin is able to prevent carcinogenesis, sensitize cancer cells to chemotherapy, and protect normal cells from chemotherapy-induced damages. In the present article, we review the preventive effect of curcumin against chemotherapy-induced myelosuppression, gastrointestinal toxicity, cardiotoxicity, hepatotoxicity, nephrotoxicity, neurotoxicity, ototoxicity, and genotoxicity, and discuss its action mechanisms
Probing Interface of Perovskite Oxide Using Surface-specific Terahertz Spectroscopy
The surface/interface species in perovskite oxides play an essential role in
many novel emergent physical phenomena and chemical processes. With low
eigen-energy in the terahertz region, such species at buried interfaces remain
poorly understood due to the lack of feasible experimental techniques. Here, we
show that vibrational resonances and two-dimensional electron gas at the
interface can be characterized using surface-specific nonlinear spectroscopy in
the terahertz range. This technique uses intra-pulse difference frequency
mixing (DFM) process, which is allowed only at surface/interface of a medium
with inversion symmetry. Sub-monolayer sensitivity can be achieved using the
state-of-the-art detection scheme for the terahertz emission from
surface/interface. As a demonstration, Drude-like nonlinear response from the
two-dimensional electron gas emerging at LaAlO3/SrTiO3 or Al2O3/ SrTiO3
interface was successfully observed. Meanwhile, the interfacial vibrational
spectrum of the ferroelectric soft mode of SrTiO3 at 2.8 THz was also obtained
that was polarized by the surface field in the interfacial region. The
corresponding surface/interface potential, which is a key parameter for
SrTiO3-based interface superconductivity and photocatalysis, can now be
determined optically via quantitative analysis on the polarized phonon
spectrum. The interfacial species with resonant frequencies in the THz region
revealed by our method provide more insights into the understanding of physical
properties of complex oxides.Comment: arXiv admin note: substantial text overlap with arXiv:2207.1461
Surface Structure of Protonated R-Sapphire (11̅02) Studied by Sum-Frequency Vibrational Spectroscopy
Sum frequency vibrational spectroscopy was used to study the protonated R-plane (1{bar 1}02 ) sapphire surface. The OH stretch vibrational spectra show that the surface is terminated with three hydroxyl moieties, two from AlOH{sub 2} and one from Al{sub 2}OH functional groups. The observed polarization dependence allows determination of the orientations of the three OH species. The results suggest that the protonated sapphire (1{bar 1}02 ) surface differs from an ideal stoichimetric termination in a manner consistent with previous X-ray surface diffraction (crystal truncation rod) studies. However, in order to best explain the observed hydrogenbonding arrangement, surface oxygen spacing determined from the X-ray diffraction study requires modification
Solitary beam propagation in a nonlinear optical resonator enables high-efficiency pulse compression and mode self-cleaning
Generating intense ultrashort pulses with high-quality spatial modes is
crucial for ultrafast and strong-field science. This can be accomplished by
controlling propagation of femtosecond pulses under the influence of Kerr
nonlinearity and achieving stable propagation with high intensity. In this
work, we propose that the generation of spatial solitons in periodic layered
Kerr media can provide an optimum condition for supercontinuum generation and
pulse compression using multiple thin plates. With both the experimental and
theoretical investigations, we successfully identify these solitary modes and
reveal a universal relationship between the beam size and the critical
nonlinear phase. Space-time coupling is shown to strongly influence the
spectral, spatial and temporal profiles of femtosecond pulses. Taking advantage
of the unique characters of these solitary modes, we demonstrate single-stage
supercontinuum generation and compression of femtosecond pulses from initially
170 fs down to 22 fs with an efficiency ~90%. We also provide evidence of
efficient mode self-cleaning which suggests rich spatial-temporal
self-organization processes of laser beams in a nonlinear resonator
Nonrelativistic and nonmagnetic control of terahertz charge currents via electrical anisotropy in RuO2 and IrO2
Precise and ultrafast control over photo-induced charge currents across
nanoscale interfaces could lead to important applications in energy harvesting,
ultrafast electronics, and coherent terahertz sources. Recent studies have
shown that several relativistic mechanisms, including inverse spin-Hall effect,
inverse Rashba-Edelstein effect and inverse spin-orbit-torque effect, can
convert longitudinally injected spin-polarized currents from magnetic materials
to transverse charge currents, thereby harnessing these currents for terahertz
generation. However, these mechanisms typically require external magnetic
fields and suffer from low spin-polarization rates and low efficiencies of
relativistic spin-to-charge conversion. In this work, we present a novel
nonrelativistic and nonmagnetic mechanism that directly utilizes the
photo-excited high-density charge currents across the interface. We demonstrate
that the electrical anisotropy of conductive oxides RuO2 and IrO2 can
effectively deflect injected charge currents to the transverse direction,
resulting in efficient and broadband terahertz radiation. Importantly, this new
mechanism has the potential to offer much higher conversion efficiency compared
to previous methods, as conductive materials with large electrical anisotropy
are readily available, whereas further increasing the spin-Hall angle of
heavy-metal materials would be challenging. Our new findings offer exciting
possibilities for directly utilizing these photo-excited high-density currents
across metallic interfaces for ultrafast electronics and terahertz
spectroscopy
Spatially homogeneous few-cycle compression of Yb lasers via all-solid-state free-space soliton management
The high power and variable repetition-rate of Yb femtosecond lasers makes them very attractive for ultrafast science. However, for capturing sub-200 fs dynamics, efficient, high-fidelity and high-stability pulse compression techniques are essential. Spectral broadening using an all-solid-state free-space geometry is particularly attractive, as it is simple, robust and low-cost. However, spatial and temporal losses caused by spatio-spectral inhomogeneities have been a major challenge to date, due to coupled space-time dynamics associated with unguided nonlinear propagation. In this work, we use all-solid-state free-space compressors to demonstrate compression of 170 fs pulses at a wavelength of 1030nm from a Yb:KGW laser to ∼9.2 fs, with a highly spatially homogeneous mode. This is achieved by ensuring that the nonlinear beam propagation in periodic layered Kerr media occurs in spatial soliton modes, and by confining the nonlinear phase through each material layer to less than 1.0 rad. A remarkable spatio-spectral homogeneity of ∼0.87 can be realized, which yields a high efficiency of >50% for few-cycle compression. The universality of the method is demonstrated by implementing high-quality pulse compression under a wide range of laser conditions. The high spatiotemporal quality and the exceptional stability of the compressed pulses are further verified by high-harmonic generation. Our predictive method offers a compact and cost-effective solution for high-quality few-cycle-pulse generation from Yb femtosecond lasers, and will enable broad applications in ultrafast science and extreme nonlinear optics.
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Interfacial structures of acidic and basic aqueous solutions
Abstract Phase-sensitive sum-frequency vibrational spectroscopy was used to study water/vapor interfaces of HCl, HI, and NaOH solutions. The measured imaginary part of the surface spectral responses provided direct characterization of OH stretch vibrations and information about net polar orientations of water species contributing to different regions of the spectrum. We found clear evidence that hydronium ions prefer to emerge at interfaces. Their OH stretches contribute to the "ice-like" band in the spectrum. Their charges create a positive surface field that tends to reorient water molecules more loosely bonded to the topmost water layer with oxygen toward the interface, and thus enhances significantly the "liquid-like" band in the spectrum. Iodine ions in solution also like to appear at the interface and alter the positive surface field by forming a narrow double-charge layer with hydronium ions. In NaOH solution, the observed weak change of the "liquid-like" band and disappearance of the "ice-like" band in the spectrum indicates that OH-ions must also have excess at the interface. How they are incorporated in the interfacial water structure is however not clear