Controllable terahertz radiation from a linear-dipole-array formed by a two-color laser filament in air

We have demonstrated the effective control on carrier-envelope phase, angular distribution as well as peak intensity of a nearly single-cycle terahertz pulse emitted from a laser filament formed by two-color, the fundamental and the corresponding second harmonics, femtosecond laser pulses propagating in air. Experimentally, such control has been performed by varying the filament length and the initial phase difference between the two-color laser components. A linear-dipole-array model, including the descriptions of the both generation (via laser field ionization) and propagation of the emitted terahertz pulse, is proposed to present a quantitative interpretation of the observations. Our results contribute to the understanding of terahertz generation in a femtosecond laser filament and suggest a practical way to control the electric field of terahertz pulse for potential applications

Frequency blue shift of terahertz radiation from femtosecond laser induced air plasmas

The peak frequency of the terahertz radiation generated from the femtosecond laser-induced air plasmas is blue shifted with the increased second harmonics intensity when a high voltage is added upon the air plasmas. This blue shift is the result of the DC-biased field from the high voltage plus the AC-biased field from the second harmonics, indicating that this terahertz radiation frequency peak is tunable by varying the two field components. This tunable frequency peak is significant to various applications such as remote sensing and material characterization

Frequency tuning for broadband terahertz emission from two-color laser-induced air plasma

Effective manipulation of broadband terahertz emission, especially on spectrum tuning, is of great importance for many applications. We demonstrate a method to realize frequency tuning of terahertz emissions from two-color laser-induced air plasmas. The terahertz central frequency is switched from 0.56 to 0.82 THz by changing the polarization state of the fundamental wave with a quarter-wave plate. Based on numerical simulation, it is found that this frequency tuning is due to the birefringence effect induced by the fundamental wave on the second harmonic inside the filament, which leads to a discrepancy on the polarization chirality of the two-color laser components. Two-color lasers with opposite chirality will emit terahertz radiation with higher central frequency compared to two-color lasers with the same chirality at moderate laser intensity

Bessel terahertz pulses from superluminal laser plasma filaments

Terahertz radiation with a Bessel beam profile is demonstrated experimentally from a two-color laser filament in air, which is induced by tailored femtosecond laser pulses with an axicon. The temporal and spatial distributions of Bessel rings of the terahertz radiation are retrieved after being collected in the far field. A theoretical model is proposed, which suggests that such Bessel terahertz pulses are produced due to the combined effects of the inhomogeneous superluminal filament structure and the phase change of the two-color laser components inside the plasma channel. These two effects lead to wavefront crossover and constructive/destructive interference of terahertz radiation from different plasma sources along the laser filament, respectively. Compared with other methods, our technique can support the generation of Bessel pulses with broad spectral bandwidth. Such Bessel pulses can propagate to the far field without significant spatial spreading, which shall provide new opportunities for terahertz applications

Spectral interference of terahertz pulses from two laser filaments in air

Spectral interference is experimentally demonstrated by two terahertz pulses emitting from filaments induced by two successive femtosecond laser pulses in air. Here, a leading pulse is set to be weaker than a trailing pulse and their temporal separation is larger than the pulse duration of the terahertz pulses. When the leading pulse is stronger than the trailing pulse, the frequency modulation within the whole terahertz envelope is greatly deteriorated due to nonlinear effects applying on the trailing pulse through the plasmas generated by the leading pulses. Such unique terahertz spectrum may find applications in terahertz spectroscopy

Apocynum venetum leaf extract alleviated doxorubicin-induced cardiotoxicity by regulating organic acid metabolism in gut microbiota

Apocynum venetum leaf is commonly utilized for its beneficial effects in reducing blood pressure, inducing sedation, promoting diuresis, anti-aging, and cardioprotection, which also exhibit positive effects on the gut microbiota. The gut microbiota plays a role as an endocrine organ by producing bioactive metabolites that can directly or indirectly impact host physiology, specifically cardiovascular diseases. In this study, main chemical components of A. venetum leaf extract (AVLE) were identified by LC-MS, and an orally administered AVLE was employed to treat mice with doxorubicin (Dox)-induced cardiotoxicity. The results showed that AVLE contained hyperoside and oganic acids. The pharmacological findings revealed that AVLE regulated the gut microbiota, resulting in a significant increase in the levels of two organic acids, indole-3-propionic acid (IPA) and acetic acid (AA). Both IPA and AA exhibited the ability to reduce BNP, CK, and LDH levels in mice with Dox-induced cardiotoxicity. Moreover, IPA demonstrated an improvement in Dox-induced cardiac injury by inhibiting apoptosis, while AA promoted increased secretion of ghrelin through the parasympathetic nervous system, subsequently reducing cardiac fibrosis by decreasing collagen I, collagen III, and activin A. Hence, our study demonstrates that AVLE exerts a beneficial cardioprotective effect by modulating the gut microbiota, providing a potential novel target for the treatment and prevention of Dox-induced cardiotoxicity

Manipulation of polarisations for broadband terahertz waves emitted from laser plasma filaments

Polarization control of broadband terahertz waves is essential for applications in many areas such as material sciences, medical and biological diagnostics, near-field communications and public securities. Conventional methods for polarization control are limited to narrow bandwidth and often with low efficiency. Here based upon theoretical and experimental studies, we demonstrate that the two-colour laser scheme in gas plasma can provide effective control of elliptically polarized terahertz waves, including their ellipticity, azimuthal angle, and chirality. This is achieved with a circularly-polarized laser at the fundamental frequency and its linearly polarized second harmonic, a controlled phase difference between these two laser components, as well as a suitable length of the laser plasma filament. A flexible control of their ellipticity and azimuthal angle is demonstrated with our theoretical model and systematic experiments. This offers a unique and flexible technique on the polarization control of broadband terahertz radiation suitable for wide applications

miR-16-1 Promotes the Aberrant -Synuclein Accumulation in Parkinson Disease via Targeting Heat Shock Protein 70

There is striking evidence that heat shock protein 70 (Hsp70) negatively regulates -synuclein aggregation, which plays a significant role in the formation and progression of Parkinson disease (PD). However, how the Hsp70 in neurons fails to prevent or even reverse -synuclein aggregation and toxicity in PD still remains to be determined. In the present study, we constructed an -synucleinoverexpressed human neuroblastoma cell line, SH-SY5Y-Syn, in which the blockage of Hsp70 promoted -synuclein aggregation. And we also found that miR-16-1 downregulated Hsp70 and promoted -synuclein aggregation in the SH-SY5Y-Syn cells. This study revealed a novel regulatory mechanism of Hsp70 expression, which might contribute to the PD development