The echo-enabled harmonic generation (EEHG) scheme holds promising prospects for efficiently generating intense coherent radiation at very high harmonics of a conventional ultraviolet seed laser. We report the lasing of the EEHG free-electron laser (FEL) at an extreme ultraviolet (EUV) wavelength with a seeded FEL facility, the Shanghai soft x-ray FEL. For the first time, we have benchmarked the basic theory of EEHG by measuring the bunching factor distributions over one octave down to the EUV region. Our results demonstrated the key advantages of the EEHG FEL, i.e., generation of very high harmonics with a small laser-induced energy spread and insensitivity to beam imperfections, and marks a great step towards fully coherent x rays with the EEHG scheme.

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We present field data and data from the literature to highlight the effects of low-tide rainfall on particulate organic carbon (POC) redistribution in intertidal landscapes. The POC exchanges reported from disparate but related studies were standardized to a storm-induced exchange rate (gPOC m 22 mmRain 21 ) and compared. Results show that these intertidal areas have a characteristic response to rainfall with an average flux of 0.040 6 0.038 gPOC m 22 mmRain 21 . Further, low-tide rainfall can entrain and redistribute 7-54% of annual sedimentary POC accumulation, or 12-75% of annual POC export, based on current outwelling assessments. Finally, we provide a conceptual model describing the variability of rainfall-driven POC exchange through the hierarchical structure of intertidal landscapes and how observations of POC flux can be expected to change across the intertidal landscape. This information should be used to guide sampling strategies for continued intertidal zone rainfall work.