<div><div><div><p>Pseudomonas syringae is an important pathogen of many agriculturally valuable crops. Among the various pathovars described P. syringae pv. syringae (Pss) has a particularly wide host range, infecting primarily woody and herbaceous host plants. The ability of Pss to cause bacterial apical necrosis of mango trees is dependent on the production of the antimetabolite toxin mangotoxin. The production of this toxin was shown to be regulated by a self-produced signaling molecule. In this study, we determined the structure of the Pss signal molecule belonging to the recently described family of diazeniumdiolate communication molecules. Employing a targeted mass spectrometry-based approach, we provide experimental evidence that the major signal produced by Pss is the volatile compound leudiazen, which controls mangotoxin production and virulence in a detached tomato leaflet infection model. Experimental results demonstrate that KMnO4 solution inactivates leudiazen and that treatment of infected leaves with KMnO₄ abolishes necrosis. This strategy represents the first example of chemically degrading a signaling molecule to interfere with bacterial communication. The application of KMnO4 solution, which is regulatorily approved in organic farming, may constitute an environmentally friendly strategy to control Pss infections.</p></div></div></div>

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Passively modelocked VECSELs continue to improve their performance in terms of output power, repetition rate and pulse duration. Recently, up to 6.4 W of average power in 28-ps pulses have been achieved from a modelocked VECSEL with an integrated saturable absorber (MIXSEL,[1]). The shortest pulse duration generated by a VECSEL was 60 fs and below 35 mW of average output power in harmonic modelocking [2]. To date, femtosecond VECSELs were based on quantum well (QW) gain structures and the average output power has been limited to <150 mW [3,4] (Fig. 1a). In contrast, modelocked VECSELs based on quantum dot (QD) gain structures have been restricted to 18 ps using QW-SESAMs [5].Here we report on record-high average output power of a femtosecond VECSEL ( Fig. 1a: 1 W, 784 fs) and present the first detailed study of femtosecond VECSELs modelocked by fast QD-SESAMs. We investigate the modelocking performance both for VECSELs with QD and QW gain structures. Based on our previous work on the influence of GDD on the pulse duration [6] we developed a top coating inspired by the work of Lumb et al. [7]. This top coating consists of 6 AlAs/Al0.2Ga0.8As pairs and a fused silica layer on top. The thicknesses are optimized using a Monte Carlo algorithm combined with a standard optimization. This provides a flat GDD with values between ±10 fs² over a range of 30 nm around the design wavelength (Fig. 1b) which is several orders of magnitude lower compared to previous designs. Furthermore, we optimized the positions of the gain layers in the standing wave pattern to broaden and flatten the spectral gain. The SESAM we used for the QW-VECSEL has a standard resonant design with QD saturable absorber. This SESAM has a fast absorption recovery component in the order of 800 fs. For the QD-VECSEL the same SESAM was made antiresonant by depositing a quarter-wave layer of fused silica on top. This leads to a higher saturation energy of the SESAM, which enables higher power levels. Additionally, the GDD is lowered to ±100 fs 2 in a 30 nm range around the design wavelength. -100 0 100 GDD (fs 2 ) 990 980 970 960 950 940 930 wavelength (nm) 10 mW 100 mW 1 W 10 W average output power 100 fs 1 ps 10 ps 100 ps pulse duration QW-or QD-VECSEL output coupler QD-SESAM c) a) b) Fig. 1 a) Overview of MIXSELs and ultrafast VECSELs with results presented here (red) and compared to QWVECSELs (green), QD-VECSELs (orange) and MIXSELs (blue). b) GDD of the VECSEL structure (red) and the antiresonant QD-SESAM (blue). c) Experimental setup consisting of the output coupler, the QW-or QD-VECSEL and the QD-SESAM.All these design improvements enabled the first operation of a QD-VECSEL in the femtosecond regime. For both, QD-and QW-based gain structures, we achieved a similar minimal pulse duration of 416 fs (QD) and 455 fs (QW) with 140 mW (QD) and 110 mW (QW) of average output power (Fig. 1b). Direct soldering of the QD-based gain chip onto a CVD diamond heat spreader and subsequent substrate removal enabled power scaling to 1 W average power with a pulse durati...