Auxin and abscisic acid antagonistically regulate ascorbic acid production via the SlMAPK8-SlARF4-SlMYB11 module in tomato.

Ascorbic acid (AsA) is a multifunctional phytonutrient that is essential for the human diet as well as plant development. While much is known about AsA biosynthesis in plants, how this process is regulated in tomato (Solanum lycopersicum) fruits remains unclear. Here, we found that auxin treatment inhibited AsA accumulation in the leaves and pericarps of tomato. The auxin response factor gene SlARF4 is induced by auxin to mediate auxin-induced inhibition of AsA accumulation. Specifically, SlARF4 transcriptionally inhibits the transcription factor gene SlMYB11, thereby modulating AsA accumulation by regulating the transcription of the AsA biosynthesis genes l-galactose-1-phosphate phosphatase, l-galactono-1,4-lactone dehydrogenase, and dehydroascorbate. By contrast, abscisic acid (ABA) treatment increased AsA accumulation in tomato under drought stress. ABA induced the expression of the mitogen-activated protein kinase gene SlMAPK8. We demonstrate that SlMAPK8 phosphorylates SlARF4 and inhibits its transcriptional activity, whereas SlMAPK8 phosphorylates SlMYB11 and activates its transcriptional activity. SlMAPK8 functions in ABA-induced AsA accumulation and drought stress tolerance. Moreover, ABA antagonizes the effects of auxin on AsA biosynthesis. Therefore, auxin- and ABA-induced regulation of AsA accumulation is mediated by the SlMAPK8-SlARF4-SlMYB11 module in tomato during fruit development and drought stress responses, shedding light on the roles of phytohormones in regulating AsA accumulation to mediate stress tolerance.

Efficient polarization-insensitive quasi-BIC modulation by VO2 thin films.

Bound states in the continuum (BIC) offer great design freedom for realizing high-quality factor metasurfaces. By deliberately disrupting the inherent symmetries, BIC can degenerate into quasi-BIC exhibiting sharp spectra with strong light confinement. This transformation has been exploited to develop cutting-edge sensors and modulators. However, most proposed quasi-BICs in metasurfaces are composed of unit cells with Cs symmetry that may experience performance degradation due to polarization deviation, posing challenges in practical applications. Addressing this critical issue, our research introduces an innovative approach by incorporating metasurfaces with C4v unit cell symmetry to eliminate polarization response sensitivity. Vanadium Dioxide (VO2) is a phase-change material with a relatively low transition temperature and reversibility. Here, we theoretically investigate the polarization-insensitive quasi-BIC modulation in Si-VO2 hybrid metasurfaces. By introducing defects into metasurfaces with Cs, C4, and C4v symmetries, we enable the emergence of quasi-BICs characterized by strong Fano resonance in their transmission spectra. Via numerically calculating the multipole decomposition, distinct dominant multipoles for different quasi-BICs are identified. A comprehensive investigation into the polarization responses of these structures under varying directions of linearly polarized light reveals the superior polarization-independent characteristics of metasurfaces with C4 and C4v symmetries, a feature that ensures the maintenance of maximum resonance peaks irrespective of polarization direction. Utilizing the polarization-insensitive quasi-BIC, we thus designed two different Si-VO2 hybrid metasurfaces with C4v symmetry. Each configuration presents complementary benefits, leveraging the VO2 phase transition's loss change to facilitate efficient modulation. Our quantitative calculation indicates notable achievements in modulation depth, with a maximum relative modulation depth reaching up to 342%. For the first time, our research demonstrates efficient modulation using polarization-insensitive quasi-BICs in designed Si-VO2 hybrid metasurfaces, achieving identical polarization responses for quasi-BIC-based applications. Our work paves the way for designing polarization-independent quasi-BICs in metasurfaces and marks a notable advancement in the field of tunable integrated devices.

High-temperature-insensitivity high-power Yb-doped fiber laser directly in-band pumping by 1018 nm laser diodes.

In this Letter, we demonstrate a high-power ytterbium-doped fiber laser (YDFL) based on a directly in-band pumping scheme (DIPS) which employs 1018 nm laser diodes (LDs) as pump sources. The wavelength of the LDs is designed theoretically, considering the distribution of Yb3+ absorption cross section (σa) as well as quantum defect (QD). The flat distribution of σa around 1018 nm ensures excellent temperature insensitivity and flexibility for the YDFL. Besides, lower QD and more compact structure promise higher optical-to-optical (O-O) and electrical-to-optical (E-O) efficiencies. Based on the experimental setup, as the cooling temperature of the 1018 nm LDs ranges from 6 to 23°C, an output power of 2 kW level is achieved that varies by only 2.01% without adjusting the operating current of the LDs subjectively. The output power is then scaled up to 5 kW level. Furthermore, there is a great potential to achieve higher output power and E-O efficiency in YDFLs based on the DIPS.

SlMYB99-mediated auxin and abscisic acid antagonistically regulate ascorbic acids biosynthesis in tomato.

Ascorbic acid (AsA) is a water-soluble antioxidant that plays important roles in plant development and human health. Understanding the regulatory mechanism underlying AsA biosynthesis is imperative to the development of high AsA plants. In this study, we reveal that the auxin response factor SlARF4 transcriptionally inhibits SlMYB99, which subsequently modulates AsA accumulation via transcriptional activation of AsA biosynthesis genes GPP, GLDH, and DHAR. The auxin-dependent transcriptional cascade of SlARF4-SlMYB99-GPP/GLDH/DHAR modulates AsA synthesis, while mitogen-activated protein kinase SlMAPK8 not only phosphorylates SlMYB99, but also activates its transcriptional activity. Both SlMYB99 and SlMYB11 proteins physically interact with each other, thereby synergistically regulating AsA biosynthesis by upregulating the expression of GPP, GLDH, and DHAR genes. Collectively, these results demonstrate that auxin and abscisic acid antagonistically regulate AsA biosynthesis during development and drought tolerance in tomato via the SlMAPK8-SlARF4-SlMYB99/11 module. These findings provide new insights into the mechanism underlying phytohormone regulation of AsA biosynthesis and provide a theoretical basis for the future development of high AsA plants via molecular breeding.

Amplification of random lasing enables a 10-kW-level high-spectral-purity Yb-Raman fiber laser.

By amplifying the cascaded random Raman fiber laser (RRFL) oscillator and ytterbium fiber laser oscillator, we present the first, to the best of our knowledge, demonstration of a 10-kW-level high-spectral-purity all-fiber ytterbium-Raman fiber amplifier (Yb-RFA). With a carefully designed backward-pumped RRFL oscillator structure, the parasitic oscillation between the cascaded seeds is avoided. Leveraging the RRFL with full-open-cavity as the Raman seed, the Yb-RFA realizes 10.7-kW Raman lasing at 1125 nm, which is beyond the operating wavelengths of all the reflection components used in the system. The spectral purity of the Raman lasing reaches 94.7% and the 3-dB bandwidth is 3.9 nm. This work paves a way to combine the temporal stability of the RRFL seed and the power scaling of Yb-RFA, enabling the wavelength extension of high-power fiber lasers with high spectral purity.

High-power and high-brightness Er:Yb codoped fiber MOPA operating at 1535 nm.

In this paper, we study the emerging 1535 nm Er: Yb codoped fiber MOPA with high power and high brightness. To characterize the interstage influence of this ASE-sensitive system, we conduct an interstage numerical model based on steady energy transfer model, where the seed and amplifier converge together. We analyze the amplifier setup, the seed pumping scheme, and feedback from inner reflection based on the model. Afterwards, we experimentally demonstrate a 1535 nm all fiber large mode area Er: Yb codoped fiber MOPA with the output power of 174.5 W, the brightness of 13.97 W/µm2sr, and ASE suppression ratio of 45 dB. To the best of our knowledge, this is the highest power and brightness of 1535 nm fiber lasers to date.

Spatiotemporal analysis of an all-fiber multimode interference-based saturable absorber via a mode-resolved nonlinear Schrodinger equation.

This paper presents an approach that combines the generalized multimode nonlinear Schrodinger equation with a transmission model to analyze spatiotemporal characteristics of multimode interference in single mode/large mode area fiber-graded-index multimode fiber-single mode fiber (SMF/LMA-GIMF-SMF) structures for the first time. Approximated self-imaging (ASIM) behavior in GIMF and the study of the latter structure used in spatiotemporal mode-locked fiber lasers are first demonstrated. Simulations show that these structures can work as saturable absorbers enabling high-energy pulse output due to nonlinear intermodal interactions and intensity-dependent multimode interference. Otherwise, underlying ASIM is proven that it can perturb the transmission of SMF/LMA-GIMF-SMF, causing instability of their saturable-absorption characteristics. This paper provides a theoretical guide for many applications, such as beam shaping, mode conversion, and high-energy ultrafast fiber laser.

Spectral pedestal during the kilowatt-level amplification of a random fiber laser operating near the lasing threshold.

The amplification of random fiber lasers (RFLs) attracts much attention due to their unique characteristics such as wavelength flexibility and low coherence. We present that, in the kilowatt-level amplification of RFL operating near its lasing threshold, a broad and flat spectral pedestal can co-exist with the narrow spectral peak of RFL. This phenomenon is different from the case in the amplification of fixed-cavity laser seeds. Time-domain measurements show that the broad and flat spectral pedestal, which extends to long wavelengths, is composed of temporal pulses, while few temporal pulses exist in the narrow spectral peak. We attribute the spectral pedestal to intensity fluctuations from the random seed laser and modulation instability in the amplification stage. Control experiments reveal that the working status of the random seed laser and the effective length of the amplifier can influence the spectral bandwidth. By taking advantage of this phenomenon, we propose a novel approach to achieve a high-power broadband light source through the amplification of RFLs operating near the lasing threshold.

219.6 W large-mode-area Er:Yb codoped fiber amplifier operating at 1600 nm pumped by 1018 nm fiber lasers.

We demonstrate, to the best of our knowledge, the first high-power large-mode-area Er:Yb codoped fiber amplifier pumped by 1018 nm fiber lasers. The output power reaches 219.6 W, which is the highest power operating at 1600 nm with near-diffraction-limitation beam quality. The 1018 nm pumping scheme contributes to the mitigation of Er,Yb fiber bottlenecking, improvement in signal gain, and reduction of heat generation. Also, we inject co-propagating C-band amplified spontaneous emission (ASE) into the master amplifier to avoid unwanted backward-propagating ASE.

Power scalability of a continuous-wave high-power Er-Yb co-doped fiber amplifier pumped by Yb-doped fiber lasers.

The power scaling of Er-Yb co-doped fiber lasers and amplifiers has been limited by the bottleneck effect of energy-transfer saturation between Yb ions and Er ions. The emerging method of Er-Yb co-doped fiber amplifiers pumped by Yb-doped fiber lasers is considered as an approach to enhance the threshold of the bottleneck effect. In this paper, we quantitatively characterize the threshold of the bottleneck effect via the method of extreme value analysis of the second-order derivative. The method facilitates the optimization of the amplifier configuration. Afterward, we numerically investigate the bottleneck effect of various Er-Yb co-doped fiber amplifiers off-peak cladding-pumped by 10××nm Yb-doped fiber lasers for what we believe, to the best of our knowledge, is the first time. The result shows that the most optimal configuration is long gain fiber over 20 m pumped by a 1020-1025 nm fiber laser, with more than two times the output limit of a conventional laser diode pumping scheme. The essential factors of an amplifier are discussed afterward, including the pump-launching direction, the optimization of large-mode-area fiber, the core-cladding ratio, the concentration of doping ions, the nonlinearity limit, and the distribution of the heat load.