We present an approach,a Terahertz streaking-assisted photoelectron spectrum(THz SAPS),to achieve direct observations of ultrafast coherence dynamics with timescales beyond the pulse duration.Using a 24 fs probe pulse...We present an approach,a Terahertz streaking-assisted photoelectron spectrum(THz SAPS),to achieve direct observations of ultrafast coherence dynamics with timescales beyond the pulse duration.Using a 24 fs probe pulse,the THz SAPS enables us to well visualize Rabi oscillations of 11.76 fs and quantum beats of 2.62 fs between the 5S_(1/2) and 5P_(3/2) in rubidium atoms.The numerical results show that the THz SAPS can simultaneously achieve high resolution in both frequency and time domains without the limitation of Heisenberg uncertainty of the probe pulse.The long probe pulse promises sufficiently high frequency resolution in photoelectron spectroscopy allowing to observe Autler-Townes splittings,whereas the streaking THz field enhances temporal resolution for not only Rabi oscillations but also quantum beats between the ground and excited states.The THz SAPS demonstrates a potential applicability for observation and manipulation of ultrafast coherence processes in frequency and time domains.展开更多
The three-dimensional thermal properties of 18-core photonic crystal fiber lasers operated under natural convection are investigated.The temperature sensing technique based on a fiber Bragg grating sensor array is pro...The three-dimensional thermal properties of 18-core photonic crystal fiber lasers operated under natural convection are investigated.The temperature sensing technique based on a fiber Bragg grating sensor array is proposed to measure the longitudinal temperature distribution of a 1.6-m-long ytterbium-doped 18-core photonic crystal fiber.The results show that the temperature decreases from the pump end to the launch end exponentially.Moreover,the radial temperature distribution of the fiber end is investigated by using the full-vector finite-element method.The numerical results match well with the experimental data and the coating temperature reaches 422.7K,approaching the critical value of polymer cladding,when the pumping power is 40 W.Therefore the fiber end cooling is necessary to achieve power scaling.Compared with natural convection methods,the copper cooling scheme is found to be an effective method to reduce the fiber temperature.展开更多
The modal of 18-core photonic crystal fiber laser is discussed and calculated.And corresponding far-field distribution of the supermodes is given by Fresnel diffraction integral.For improving beam quality,the mode sel...The modal of 18-core photonic crystal fiber laser is discussed and calculated.And corresponding far-field distribution of the supermodes is given by Fresnel diffraction integral.For improving beam quality,the mode selection method based on the Talbot effect is introduced.The reflection coefficients are calculated,and the result shows that an in-phase supermode can be locked better at a large propagation distance.展开更多
Conventional analytical methods in the wavelet domain are used to present an analysis of terahertz （THz） waveguide modes.To obtain THz radiation pulses passing through a waveguide,we build a simple experimental syst...Conventional analytical methods in the wavelet domain are used to present an analysis of terahertz （THz） waveguide modes.To obtain THz radiation pulses passing through a waveguide,we build a simple experimental system with a 5-mm-long,230-μm-inner-diameter stainless steel waveguide.The single-mode guided signal from the experiments and the multi-mode signal of a similar THz waveguide reported in the literature are analyzed using the continuous wavelet transform （CWT）.The results demonstrate that analyzing THz waveguide modes in the wavelet domain not only possesses all the functionality of the traditional THz time-domain spectroscopy （TDS） data processing but also has the ability to unscramble quantitatively and intuitively detailed information about the target samples,such as mode type,cut-off frequency,amplitude distinction,and group velocity.展开更多
基金Supported by the National Natural Science Foundation of China(Grant Nos.11827806,11874368 and 61675213).
文摘We present an approach,a Terahertz streaking-assisted photoelectron spectrum(THz SAPS),to achieve direct observations of ultrafast coherence dynamics with timescales beyond the pulse duration.Using a 24 fs probe pulse,the THz SAPS enables us to well visualize Rabi oscillations of 11.76 fs and quantum beats of 2.62 fs between the 5S_(1/2) and 5P_(3/2) in rubidium atoms.The numerical results show that the THz SAPS can simultaneously achieve high resolution in both frequency and time domains without the limitation of Heisenberg uncertainty of the probe pulse.The long probe pulse promises sufficiently high frequency resolution in photoelectron spectroscopy allowing to observe Autler-Townes splittings,whereas the streaking THz field enhances temporal resolution for not only Rabi oscillations but also quantum beats between the ground and excited states.The THz SAPS demonstrates a potential applicability for observation and manipulation of ultrafast coherence processes in frequency and time domains.
基金Supported by the National Basic Research Program of China under Grant No 2010CB327801the Key Program of National Natural Science Foundation of China under Grant No 60637010THE Natural Science Research Project in University of Hebei Province under Grant No Z2010163.
文摘The three-dimensional thermal properties of 18-core photonic crystal fiber lasers operated under natural convection are investigated.The temperature sensing technique based on a fiber Bragg grating sensor array is proposed to measure the longitudinal temperature distribution of a 1.6-m-long ytterbium-doped 18-core photonic crystal fiber.The results show that the temperature decreases from the pump end to the launch end exponentially.Moreover,the radial temperature distribution of the fiber end is investigated by using the full-vector finite-element method.The numerical results match well with the experimental data and the coating temperature reaches 422.7K,approaching the critical value of polymer cladding,when the pumping power is 40 W.Therefore the fiber end cooling is necessary to achieve power scaling.Compared with natural convection methods,the copper cooling scheme is found to be an effective method to reduce the fiber temperature.
基金supported by the National Basic Research Program of China(No.2010CB327801)the Key Program of National Natural Science Foundation of China(No.60637010)
文摘The modal of 18-core photonic crystal fiber laser is discussed and calculated.And corresponding far-field distribution of the supermodes is given by Fresnel diffraction integral.For improving beam quality,the mode selection method based on the Talbot effect is introduced.The reflection coefficients are calculated,and the result shows that an in-phase supermode can be locked better at a large propagation distance.
基金supported by the National "973" Project of China(No. 2007CB310408)the National Natural Science Foundation of China(No. 60578037)+3 种基金the National Natural Science Foundation of China-Rassian Foundation for Basic Research Program 2007-2008(No. 60711120198)the Major Project of Tianjin Sci-Tech Support Program(No. 08ZCKFZC28000)the International Joint Program in Tianjin(No. 07ZCGHH01100)the Project 985 Program of Tianjin University
文摘Conventional analytical methods in the wavelet domain are used to present an analysis of terahertz （THz） waveguide modes.To obtain THz radiation pulses passing through a waveguide,we build a simple experimental system with a 5-mm-long,230-μm-inner-diameter stainless steel waveguide.The single-mode guided signal from the experiments and the multi-mode signal of a similar THz waveguide reported in the literature are analyzed using the continuous wavelet transform （CWT）.The results demonstrate that analyzing THz waveguide modes in the wavelet domain not only possesses all the functionality of the traditional THz time-domain spectroscopy （TDS） data processing but also has the ability to unscramble quantitatively and intuitively detailed information about the target samples,such as mode type,cut-off frequency,amplitude distinction,and group velocity.
