The development of high-intensity ultrafast laser facilities provides the possibility to create novel physical phenomena and matter states.The timing fluctuation of the laser pulses is crucial for pump–probe experime...The development of high-intensity ultrafast laser facilities provides the possibility to create novel physical phenomena and matter states.The timing fluctuation of the laser pulses is crucial for pump–probe experiments,which is one of the vital means to observe the ultrafast dynamics driven by intense laser pulses.In this paper,we demonstrate the timing fluctuation characterization and control of the front end of a 100-PW laser that is composed of a high-contrast optical parametric amplifier(seed)and a 200-TW optical parametric chirped pulse amplifier(preamplifier).By combining the timing jitter measurement with a feedback system,the laser seed and preamplifier are synchronized to the reference with timing fluctuations of 1.82 and 4.48 fs,respectively.The timing system will be a key prerequisite for the stable operation of 100-PW laser facilities and provide the basis for potential pump–probe experiments performed on the laser.展开更多
An all-optical clock recovery scheme based on monolithic amplified feedback DFB laser （AFL） diode is proposed for nonreturn-to-zero （NRZ） quadrature phase shift keying （QPSK） format signals. By using a preproces...An all-optical clock recovery scheme based on monolithic amplified feedback DFB laser （AFL） diode is proposed for nonreturn-to-zero （NRZ） quadrature phase shift keying （QPSK） format signals. By using a preprocessing stage, clock recovery （CR） is successfully demonstrated for 40-Gbaud NRZ-QPSK signals based on this scheme. The dependence of the timing jitter of the recovered clock on the optical power of the injected signal is investigated. A minimum timing jitter of 362.8 fs （integrated within a frequency range from 10 Hz to 10 MHz） is obtained.展开更多
Corrective feedback is an important part of second language acquisition, and many researches have showed that the corrective feedback in general have a positive effect on second language acquisition. The present study...Corrective feedback is an important part of second language acquisition, and many researches have showed that the corrective feedback in general have a positive effect on second language acquisition. The present study aims to investigate corrective feedback and draw enlightening conclusions:1) Different corrective feedback types have different effects on second language acquisition; 2)The effect of corrective feedback is also influenced by the feedback timing, explicitness of the feedback and learners' individual differences; 3) Teachers should consider feedback types, feedback timing, and individual differences of students based on teaching contents when providing corrective feedback in foreign language teaching.展开更多
FERMI, the seeded free electron laser(FEL) in operation in Italy, is providing the User Community with unique fully coherent radiation, in the wavelength range 100–4 nm. FERMI is the first FEL fully synchronized by m...FERMI, the seeded free electron laser(FEL) in operation in Italy, is providing the User Community with unique fully coherent radiation, in the wavelength range 100–4 nm. FERMI is the first FEL fully synchronized by means of optical fibers. The optical timing system ensures an ultra-stable phase reference to its distributed clients. Several femtosecond longitudinal diagnostics verify the achieved performance; the bunch length monitor(BLM) and the bunch arrival monitor(BAM) will be presented in this paper. Feedback systems play a crucial role to guarantee the needed longterm electron beam stability. A real-time infrastructure allows shot-to-shot communication between front-end computers and the servers. Orbit feedbacks are useful in machine tuning, whereas longitudinal feedbacks control electron energy,compression and arrival time. A flexible software framework allows a rapid implementation of heterogeneous multiinput–multi-output(MIMO) longitudinal loops simply by selecting the appropriate sensors and actuators.展开更多
A high-quality low-timing-jitter 20-GHz optical pulse train is generated by using two cascaded sinusoidally driven electroabsorption modulators （EAMs） at very low bias voltage of -0.8 V in conjunction with atunable ...A high-quality low-timing-jitter 20-GHz optical pulse train is generated by using two cascaded sinusoidally driven electroabsorption modulators （EAMs） at very low bias voltage of -0.8 V in conjunction with atunable distributed feedback （DFB） semiconductor laser. An approximate transform-limited optical pulse, with the pulse width less than 7 ps, the spectral width of 0.3 nm, and the side-mode suppression ratio （SMSR） above 20 dB, is obtained by tuning the optical delay line.展开更多
基金supported by the Shanghai High Repetition Rate XFEL and Extreme Light Facility (SHINE) projectthe National Natural Science Foundation of China (62105346)+2 种基金the CAS Project for Young Scientists in Basic Research(YSBR-059)the 100 Talents Program of CASthe Basic Research Project of the Shanghai Science and Technology Innovation Action Plan (20JC1416000)
文摘The development of high-intensity ultrafast laser facilities provides the possibility to create novel physical phenomena and matter states.The timing fluctuation of the laser pulses is crucial for pump–probe experiments,which is one of the vital means to observe the ultrafast dynamics driven by intense laser pulses.In this paper,we demonstrate the timing fluctuation characterization and control of the front end of a 100-PW laser that is composed of a high-contrast optical parametric amplifier(seed)and a 200-TW optical parametric chirped pulse amplifier(preamplifier).By combining the timing jitter measurement with a feedback system,the laser seed and preamplifier are synchronized to the reference with timing fluctuations of 1.82 and 4.48 fs,respectively.The timing system will be a key prerequisite for the stable operation of 100-PW laser facilities and provide the basis for potential pump–probe experiments performed on the laser.
基金This work was supported by the National ＂973＂ Program of China （No. 2011CB301702）, in part by the National ＂863＂ Program of China （No. 2013AA014202）, and the National Natural Science Foundation of China （Nos. 61201103, 61335009, 61274045, and 61205031）.
文摘An all-optical clock recovery scheme based on monolithic amplified feedback DFB laser （AFL） diode is proposed for nonreturn-to-zero （NRZ） quadrature phase shift keying （QPSK） format signals. By using a preprocessing stage, clock recovery （CR） is successfully demonstrated for 40-Gbaud NRZ-QPSK signals based on this scheme. The dependence of the timing jitter of the recovered clock on the optical power of the injected signal is investigated. A minimum timing jitter of 362.8 fs （integrated within a frequency range from 10 Hz to 10 MHz） is obtained.
文摘Corrective feedback is an important part of second language acquisition, and many researches have showed that the corrective feedback in general have a positive effect on second language acquisition. The present study aims to investigate corrective feedback and draw enlightening conclusions:1) Different corrective feedback types have different effects on second language acquisition; 2)The effect of corrective feedback is also influenced by the feedback timing, explicitness of the feedback and learners' individual differences; 3) Teachers should consider feedback types, feedback timing, and individual differences of students based on teaching contents when providing corrective feedback in foreign language teaching.
基金the Italian Minister of University and Research(MIUR)the Regione Autonoma Friuli Venezia Giulia+2 种基金the European Investment Bank(EIB)the European Research Council(ERC)the European Commission(EC)
文摘FERMI, the seeded free electron laser(FEL) in operation in Italy, is providing the User Community with unique fully coherent radiation, in the wavelength range 100–4 nm. FERMI is the first FEL fully synchronized by means of optical fibers. The optical timing system ensures an ultra-stable phase reference to its distributed clients. Several femtosecond longitudinal diagnostics verify the achieved performance; the bunch length monitor(BLM) and the bunch arrival monitor(BAM) will be presented in this paper. Feedback systems play a crucial role to guarantee the needed longterm electron beam stability. A real-time infrastructure allows shot-to-shot communication between front-end computers and the servers. Orbit feedbacks are useful in machine tuning, whereas longitudinal feedbacks control electron energy,compression and arrival time. A flexible software framework allows a rapid implementation of heterogeneous multiinput–multi-output(MIMO) longitudinal loops simply by selecting the appropriate sensors and actuators.
基金This work was supported by Hundreds of Talents Plan of CAS.
文摘A high-quality low-timing-jitter 20-GHz optical pulse train is generated by using two cascaded sinusoidally driven electroabsorption modulators （EAMs） at very low bias voltage of -0.8 V in conjunction with atunable distributed feedback （DFB） semiconductor laser. An approximate transform-limited optical pulse, with the pulse width less than 7 ps, the spectral width of 0.3 nm, and the side-mode suppression ratio （SMSR） above 20 dB, is obtained by tuning the optical delay line.
