Dispersion of the third-order optical nonlinearities in 2D (PEA)2PbI4 perovskite film.

We report the wavelength-dependent third-order optical nonlinearity of two-dimensional halide organic-inorganic perovskite (PEA)2PbI4 film experimentally. The high-quality two-dimensional (PEA)2PbI4 film prepared via confinement-assisted drop-casting process exhibits ultrafast optical response and large third-order optical nonlinearities, and the measured nonlinear refractive index is closer to the quantum perturbation model accounting for the excitonic effect. In addition, the wavelength-dependent optical response transition from self-focusing to self-defocusing, saturable absorption to reverse saturable absorption has been observed and investigated. The experimental results confirm the large third-order optical nonlinearities in (PEA)2PbI4 film and may make inroads toward developing cost-effective high-performance optoelectronic devices.

1.7†µm sub-200 fs vortex beams generation from a thulium-doped all-fiber laser.

The pulsed 1.7 µm vortex beams (VBs) has significant research prospects in the fields of imaging and material processing. We experimentally demonstrate the generation of sub-200 fs pulsed VBs at 1.7 µm based on a home-made mode-selective coupler (MSC). Through dispersion management technology in a thulium-doped fiber laser, the stable linearly polarized VBs pulse directly emitting from the cavity is measured to be 186 fs with central wavelength of 1721.2 nm. By controlling the linear superposition of LP11 modes, cylindrical vector beams (CVBs) can also be obtained. In addition, a variety of bound states pulsed VBs at 1.7 µm can also be observed. Our finding provides an effective way to generate ultrashort pulsed VBs and CVBs at 1.7 µm waveband.

High-damage-threshold mid-infrared saturable absorber enabled by tantalum carbide nanoparticles.

A stable mid-infrared saturable absorber with a high damage threshold is urgently required for high-performance optical modulation in the mid-infrared regime. Here, we demonstrate stable mid-infrared erbium-doped fiber laser generation modulated by tantalum carbide nanoparticles (TaC NPs) experimentally. The TaC NPs show high physicochemical stability, obvious nonlinear optical absorption, and a high damage threshold. By introducing the TaC-based saturable absorber into an erbium-doped fiber laser, stable nanosecond pulses can be successfully delivered with a minimum pulse duration of 575 ns and signal-to-noise ratio of over 40 dB. The experimental results show that TaC NPs can act as a stable mid-infrared pulse modulator, and may make inroads for developing highly stable broadband optoelectronic devices.

scKINETICS: inference of regulatory velocity with single-cell transcriptomics data.

MOTIVATION: Transcriptional dynamics are governed by the action of regulatory proteins and are fundamental to systems ranging from normal development to disease. RNA velocity methods for tracking phenotypic dynamics ignore information on the regulatory drivers of gene expression variability through time. RESULTS: We introduce scKINETICS (Key regulatory Interaction NETwork for Inferring Cell Speed), a dynamical model of gene expression change which is fit with the simultaneous learning of per-cell transcriptional velocities and a governing gene regulatory network. Fitting is accomplished through an expectation-maximization approach designed to learn the impact of each regulator on its target genes, leveraging biologically motivated priors from epigenetic data, gene-gene coexpression, and constraints on cells' future states imposed by the phenotypic manifold. Applying this approach to an acute pancreatitis dataset recapitulates a well-studied axis of acinar-to-ductal transdifferentiation whilst proposing novel regulators of this process, including factors with previously appreciated roles in driving pancreatic tumorigenesis. In benchmarking experiments, we show that scKINETICS successfully extends and improves existing velocity approaches to generate interpretable, mechanistic models of gene regulatory dynamics. AVAILABILITY AND IMPLEMENTATION: All python code and an accompanying Jupyter notebook with demonstrations are available at http://github.com/dpeerlab/scKINETICS.

Epigenetic plasticity cooperates with cell-cell interactions to direct pancreatic tumorigenesis.

The response to tumor-initiating inflammatory and genetic insults can vary among morphologically indistinguishable cells, suggesting as yet uncharacterized roles for epigenetic plasticity during early neoplasia. To investigate the origins and impact of such plasticity, we performed single-cell analyses on normal, inflamed, premalignant, and malignant tissues in autochthonous models of pancreatic cancer. We reproducibly identified heterogeneous cell states that are primed for diverse, late-emerging neoplastic fates and linked these to chromatin remodeling at cell-cell communication loci. Using an inference approach, we revealed signaling gene modules and tissue-level cross-talk, including a neoplasia-driving feedback loop between discrete epithelial and immune cell populations that was functionally validated in mice. Our results uncover a neoplasia-specific tissue-remodeling program that may be exploited for pancreatic cancer interception.

Compact nanosecond Yb:YAG/V:YAG solid-state laser generating switchable radially and azimuthally beams.

We demonstrated a compact self-starting nanosecond Yb:YAG/V:YAG solid-state laser with cylindrical vector beams output modulated by the intracavity mode converter S-waveplate experimentally. We can deliver the stable Q-switched pulse with the highest repetition rate 3.61 kHz and minimum pulse width 26 ns at the wavelength of 1030.07 nm with the help of the V:YAG crystal. In addition, the switchable radially and azimuthally polarized beams can be realized with polarization extinction ratios of 92.3% and 89.6%, respectively. The compact laser configuration can provide solutions for generating stable nanosecond structured light, and may benefit the applications like micro/nano material processing.

Broadband saturable absorption of indium tin oxide nanocrystals toward mid-infrared regime.

We experimentally demonstrate the ultrabroadband optical nonlinearity of indium tin oxide nanocrystals (ITO NCs) in the mid-infrared regime. Especially, the ITO NCs show considerable saturation absorption behavior with large modulation depth covering the spectral range from 2-µm to 10-µm wavelength. We also demonstrate the application of the optical nonlinearity to successfully modulate the erbium-doped fluoride fiber laser to deliver a nanosecond pulse with a signal-to-noise ratio over 43 dB at 2.8-µm wavelength. The results provide a promising platform for the development of ITO-based broadband and robust optoelectronic devices toward the deep mid-infrared spectral range.

Visible optical nonlinearity of vanadium dioxide dispersions.

Vanadium dioxide (VO2), a correlated oxide compound, is one of the functional materials extensively studied in solid state physics due to its attractive physical properties. However, the nonlinear optical response of VO2 and related all-optical applications have been paid less attention. Here, the nonlinear refractive index (n 2) and third-order nonlinear susceptibility (χ (3)) of VO2 dispersions have been acquired to be 3.06 × 10-6 cm2 W-1 and 1.68 × 10-4 esu at a wavelength of 671 nm, and 5.17 × 10-6 cm2 W-1 and 2.83 × 10-4 esu at a wavelength of 532 nm via the spatial self-phase modulation (SSPM) and spatial cross-phase modulation (SXPM) effects in the visible regime, respectively. Based on the excellent nonlinear optical properties of VO2 dispersions, the proof-of-principle functions such as optical logic or-gates, all-optical switches, and inter-channel information transfer are implemented in the visible wavelength. The experimental results on the response time of VO2 to light indicate that the formation of diffraction rings is mainly an electronically coherent third-order nonlinear optical process. The experimental results show that the VO2 dispersions exhibit an excellent nonlinear optical response and may lay the foundation for the application of VO2-based all-optical devices.

Chiral wheel anions of copper(II)-early lanthanides(III) with high optical-limiting properties.

A new family of chiral wheel anions {CuII22LnIII4} (La, Ce, Pr, Nd and Sm) was obtained from aqueous solution by the use of tartrate anions. It was found that these compounds, {CuII22SmIII4} in particular, exhibit remarkable optical-limiting properties.

Highly stable soliton and bound soliton generation from a fiber laser mode-locked by VSe2 nanosheets.

We demonstrate the highly stable soliton generation from a fiber laser mode-locked by the VSe2 nanosheets experimentally. The VSe2 nanosheets prepared via the liquid phase exfoliation method exhibit ultrafast relaxation time and excellent nonlinear optical behavior with saturation intensity and modulation depth of 14.28 MW/cm2 and 19.11%, respectively. A highly stable mode-locked Er3+-doped fiber laser with pulse duration of 714 fs and signal-to-noise ratio of 78.44 dB has been delivered successfully based on the VSe2 nanosheets saturable absorber. In addition, the transition from the conventional soliton to bound-state soliton has been observed experimentally. Our results reveal that VSe2 nanosheets possess excellent nonlinear optical performance and can act as a robust optical platform for versatile optical applications.

High energy switchable pulsed High-order Mode beams in a mode-locking Raman all-fiber laser with high efficiency.

High energy pulsed High-order Mode (HOM) beams has great potential in materials processing and particle acceleration. We experimentally demonstrate a high energy mode-locking Raman all-fiber laser with switchable HOM state. A home-made fiber mode-selective coupler (MSC) is used as the mode converter with a wide bandwidth of 60 nm. By combining advantages of MSC and stimulated Raman scattering, 1.1 µJ pulsed HOM beams directly emitting from the all-fiber cavity can be achieved. After controlling the category and phase delay of vector modal superposition, different pulsed HOM beams including cylindrical vector beams (CVBs) (radial and angular) and optical vortex beams (OVBs) are reasonably obtained with high purity (all over 95%), as well as arbitrary switching. Furtherly, the slope efficiency of HOM beams in the mode-locking and continuous wave operations are as much as 20.3% and 31.8%, respectively. It may provide an effective way to achieve high energy pulsed HOM beams.

Intestinal CD11b+ B Cells Ameliorate Colitis by Secreting Immunoglobulin A.

The intestinal mucosal immune environment requires multiple immune cells to maintain homeostasis. Although intestinal B cells are among the most important immune cells, little is known about the mechanism that they employ to regulate immune homeostasis. In this study, we found that CD11b+ B cells significantly accumulated in the gut lamina propria and Peyer's patches in dextran sulfate sodium-induced colitis mouse models and patients with ulcerative colitis. Adoptive transfer of CD11b+ B cells, but not CD11b-/- B cells, effectively ameliorated colitis and exhibited therapeutic effects. Furthermore, CD11b+ B cells were found to produce higher levels of IgA than CD11b- B cells. CD11b deficiency in B cells dampened IgA production, resulting in the loss of their ability to ameliorate colitis. Mechanistically, CD11b+ B cells expressed abundant TGF-ß and TGF-ß receptor II, as well as highly activate phosphorylated Smad2/3 signaling pathway, consequently promoting the class switch to IgA. Collectively, our findings demonstrate that CD11b+ B cells are essential intestinal suppressive immune cells and the primary source of intestinal IgA, which plays an indispensable role in maintaining intestinal homeostasis.

Watt-level superfluorescent fiber source near 3 µm.

We report a watt-level mid-infrared (mid-IR) superfluorescent fiber source from ${{\rm Er}^{3 +}}$-doped ZBLAN fiber near 3 µm spectral range. With the power amplifier configuration, the mid-IR superfluorescent fiber source with power up to 1.85 W has been delivered successfully with slope efficiency about 18.6%. The experimental results may pave an avenue toward a high-power, high-temporal-stability superfluorescent source for versatile mid-IR applications.

Correlation between geometric parametric instability sidebands in graded-index multimode fibers.

The spectral analysis of the light propagating in normally dispersive graded-index multimode fibers is performed under initial noisy conditions. Based on the obtained spectra with multiple simulations in the presence of noise, we investigate the correlation in energy between the well-separated spectral sidebands through both the scattergrams and the frequency-dependent energy correlation map and find that conjugate couples are highly correlated while cross-combinations exhibit a very poor degree of correlation. These results reveal that the geometric parametric instability processes associated with each sideband pair occur independently from each other, which can provide significant insights into the fundamental dynamical effect of the geometric parametric instability and facilitate the future implementation of high-efficiency photon pair sources with reduced Raman decorrelations.

Thermally switchable bifunctional plasmonic metasurface for perfect absorption and polarization conversion based on VO2.

Perfect absorption and polarization conversion of electromagnetic wave (EM) are of significant importance for numerous optical applications. Vanadium dioxide (VO2), which can be converted from insulating state to metallic state by being exposed to different temperatures, is introduced into a metallic square loop to constitute a switchable bifunctional plasmonic metasurface for perfect absorption and polarization conversion. Combined theoretical analyses and numerical simulations, the results show that at temperature T = 356 K, the metasurface acts as a perfect absorber with nearly 91% absorptance at the wavelength of 1547 nm. When the temperature decreases to T = 292 K, the metasurface expresses as a high efficiency (about 94%) polarization converter with the polarization conversion ratio up to 86% around 1550 nm. The designed bifunctional metasurface has plenty of potential applications such as energy harvesting, optical sensing and imaging. Moreover, it can also provide guidance to research tunable, smart and multifunctional devices.

Sub-hundred nanosecond pulse generation from a black phosphorus Q-switched Er-doped fiber laser.

Black phosphorus (BP), a prosperous two-dimensional optoelectronic material, has been deeply developed for various optoelectronics applications. Here, we demonstrate a sub-hundred nanosecond passively Q-switched Er-doped all-fiber laser with BP as the saturable absorber (SA). The BP-SA is fabricated by a controllable optical deposition technique. To achieve the sub-hundred nanosecond Q-switching output, we deliberately enlarge the modulation depth of the BP-SA by suitably increasing the time and laser power of the optical deposition and shortening the laser cavity length with an integrated multifunctional component. A stable Q-switched pulse train was obtained with a pulse duration as narrow as 91 ns, and the Q-switched lasing characteristics based on the BP-SA have also been investigated and discussed. The experimental results indicate that the BP material can be employed as an effective SA for the nanosecond pulse generation.

The correlation between phase transition and photoluminescence properties of CsPbX3 (X= Cl, Br, I) perovskite nanocrystals.

We report a correlation between the structural phase transition of CsPbX3 (X=Cl, Br, I) nanocrystals (NCs) and their temperature dependent steady-state photoluminescence (PL) and time-resolved PL (TRPL). In constrast to CsPbBr3 and CsPbI3 NCs which exhibited a continuous blue shift in their bandgap with increasing temperature, the CsPbCl3 exhibited a blue shift until ~193 K, followed by a red shift until room temperature. We attribute this change from a blue to a red shift to a structural phase transtion in CsPbCl3, which also manifested in the temperature dependent TRPL. Notably, the exciton recombination lifetimes showed a similar reverse trend due to the phase transition in CsPbCl3, which has not been reported previously.

Emission of multiple resonant radiations by spatiotemporal oscillation of multimode dark pulses.

In this paper, we illustrate how the periodically modulated nonlinear parameter induced by the spatial beam oscillation can be used to generate broadband resonant radiations, through a train of dark pulses in normally dispersive graded-index multimode fibers under the efficient quasi-phase-matching schemes. More precisely, we demonstrate that two co-propagating waves with equal intensities and certain temporal delays can induce the formation of a train of dark solitons, with each emitting multiple resonant radiation lines, which can possibly form multiple radiation continuums based on vast amount of excited dark solitons. The nonlinear-interaction-aided excitation of dark pulses and their radiations appear to occur through a deterministic pathway, in sharp contrast to the situation for bright pulses in the anomalous dispersion region. The quasi-phase-matching condition via periodic oscillation of spatial beam in the normal-dispersion regime adds a unique dimension to the physical design of multimode waveguides, allowing the spectrum to be engineered for specific applications.

Broadband Nonlinear Optical Response of Single-Crystalline Bismuth Thin Film.

Bismuth (Bi), a topological material, where many interesting condensed matter phenomena have been observed, possesses unique physical properties when its thickness is reduced to thin film. Here, we prepared the highly stable, single-crystalline, continuous Bi thin film via the vapor deposition (VD) method and found that the Bi thin film can exhibit broadband, ultrafast nonlinear optical response with low saturable intensity ranging from the near-infrared to mid-infrared spectral range under strong excitation. Moreover, we demonstrated that the Bi thin film was favorable to act as a nonlinear pulse modulator toward a high performance pulsed laser operating in optical communication and mid-infrared wavelengths. The experimental results highlight the prospects of Bi thin film as broadband pulsed modulators and may open new avenues toward advanced Bi-based broadband photonic devices.

CD1d highly expressed on DCs reduces lung tumor burden by enhancing antitumor immunity.

Dendritic cells (DCs), as professional antigen­presenting cells are essential for the initial activation of adaptive antitumor immunity. CD1d is considered to present phospholipid and glycosphingolipid antigens to NKT cells. However, it is currently unknown whether CD1d expression on DCs is capable of enhancing antitumor immunity, particularly T­cell related immunity. We observed that CD1d was predominantly expressed on DCs in 3LL tumor­bearing mice, whilst a deficiency of CD1d promoted tumor growth. Notably, CD1d expression on DCs was not only required for presenting antigen to NKT cells, but also markedly promoted CD4+T and CD8+T cell activation, particularly cytotoxic T cells. All the T cells (NKT, CD4+T and CD8+T cells) upregulated CD69, CD107a and IFN­Î³ after the adoptive transfer of CD1d­positive DCs (CD1d+DCs) and tumor growth was suppressed. With regard to the mechanism, we revealed that CD1d+DCs were concomitant with a higher expression of costimulatory molecules (CD40, CD80 and CD86) and MHCI/II, which are essential for DCs to present antigens to T cells. Consistently, CD1d+DCs displayed stronger activation­associated­ERK1/2 and NF­κB signals; whereas JAK2­STAT3/6 signaling was required for maintaining a high level of CD1d on DCs. In lung cancer patients, the antitumor activities of all the T cells were enhanced with the increase of CD1d+DCs. Analysis of TCGA data revealed that high levels of CD1d indicated better outcomes for patients. Collectively, CD1d enhanced DC­based antitumor immunity, not only by targeting NKT, but also by activating CD4+T and CD8+T cells. CD1d+DCs may be superior to the bulk population of DCs in cancer immunotherapy.