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A stable 50 mJ three-channel optical waveform synthesizer is demonstrated and used to reproducibly generate a high-order harmonics supercontinuum in the soft-x-ray region. This synthesizer is composed of pump pulses from a 10-Hz-repetition-rate Ti:sapphire pump laser and signal and idler pulses from an infrared two-stage optical parametric amplifier driven by this pump laser. With the full active stabilization of all relative time delays, relative phases, and the carrier-envelope phase, a shot-to-shot stable intense continuum harmonic spectrum is obtained around 60 eV with pulse energy above 0.24 µJ. The peak power of the soft-x-ray continuum is evaluated to be beyond 1 GW with a 140 as transform limit duration. Furthermore, we found a characteristic delay dependence of the multi-cycle waveform synthesizer and established its control scheme. Compared with the one-color case, we experimentally observe an enhancement of the cut-off spectrum intensity by one to two orders of magnitude through the three-color waveform synthesis.

Background During the coronavirus disease 2019 (COVID-19) epidemic, due to the traffic blockade and the shortage of medical resources, more and more premature infants could not receive timely and effective ROP screening, which delayed treatment and even caused children blindness. Therefore, how to carry out ROP screening safely and effectively during the epidemic was very important and urgent. This study aimed to evaluate the safety and feasibility of ROP screening assisted by telemedicine network during COVID-19 outbreak. Methods This retrospective study was conducted at Wuhan Children’s hospital in Wuhan, China, from January to October, 2020. The measures which were performed to make the ROP screening more safe and effective were summarized and the comparison between ROP screening assisted by telemedicine network in 2020 and usual screening in 2019 were analyzed. Results A total of 267 outpatient infants completed ROP screening. The median gestational age was 32 weeks (30w to 34w) and the median birth weight was 1780 g (1460 g to 2100 g). Meanwhile, 149 (55.8%) out of 267 infants were males. During January to May in 2020, 86 screening appointments were received, among which 67 (77.9%) were from telemedicine platform online. The completing percentage of total online ROP appointments was higher than that of total face-to-face appointments (58.1% VS 22. 1%, P = 0.018). As for the number of infants screened between 2020 and 2019 from Februaryto October, 54 infants completed ROP screening in 2020, which was higher than that (51participants) in 2019 on September. Furthermore, compared with the usual screening in 2019, ROP screening assisted by telemedicine network in 2020 had smaller gestational age (32w VS 33w, p<0.001) and lower birth weight (1780 g VS 1900 g, p = 0.001). However, of the 267 infants screened, 18(6.7%) had ROP while the percentage of ROP screened in 2019 was the same (44[6.7%]). During follow-up, none of medical staffs was infected and no adverse reaction was reported. Conclusions The screening for retinopathy of prematurity assisted by telemedicine network was safe and feasible during the COVID-19 pandemic. Preventive measures before and after screening were very necessary, which could effectively avoid cross infection.

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