The spatial chirp generated in the Ti：sapphire multipass amplifier is numerically investigated based on the one- dimensional （1D） and two-dimensional （2D） Frantz-Nodvik equations. The simulation indicates that th...The spatial chirp generated in the Ti：sapphire multipass amplifier is numerically investigated based on the one- dimensional （1D） and two-dimensional （2D） Frantz-Nodvik equations. The simulation indicates that the spatial chirp is induced by the spatially inhomogeneous gain, and it can be almost eliminated by utilization of proper beam profiles and spot sizes of the signal and pump pulses, for example, the pump pulse has a top-hatted beam profile and the signal pulse has a super-Gaussian beam profile with a relatively larger spot size. In this way, a clear understanding of spatial chirp mechanisms in the Ti：sapphire multipass amplifier is proposed, therefore we can effectively almost eliminate the spatial chirp and improve the beam quality of a high-power Ti：sapphire chirped pulse amplifier system.展开更多
With a three-dimensional semiclassical ensemble method, we theoretically investigated the nonsequential double ionization of Ar driven by the spatially inhomogeneous few-cycle negatively chirped laser pulses. Our resu...With a three-dimensional semiclassical ensemble method, we theoretically investigated the nonsequential double ionization of Ar driven by the spatially inhomogeneous few-cycle negatively chirped laser pulses. Our results show that the recollision time window can be precisely controlled within an isolated time interval of several hundred attoseconds, which is useful for understanding the subcycle correlated electron dynamics. More interestingly, the correlated electron momentum distribution (CEMD) exhibits a strong dependence on laser intensity. That is, at lower laser intensity, CEMD is located in the first quadrant. As the laser intensity increases,CEMD shifts almost completely to the second and fourth quadrants, and then gradually to the third quadrant.The underlying physics governing the CEMD's dependence on laser intensity is explained.展开更多
<p> <span style="font-family:;" "="">The Ugandan economy is largely dependent on rural-based and rain-fed agriculture. This creates a critical need to understand the rainfall dynam...<p> <span style="font-family:;" "="">The Ugandan economy is largely dependent on rural-based and rain-fed agriculture. This creates a critical need to understand the rainfall dynamics at the local scale. However, the country has a sternly sparse and unreliable rain gauge network. This research, therefore, set</span><span style="font-family:;" "="">s</span><span style="font-family:;" "=""> out to evaluate the use of </span><span style="font-family:;" "="">the </span><span style="font-family:;" "="">CHIRPS satellite gridded dataset as an alternative rainfall estimate for local modelling of rainfall in Uganda. Complete, continuous and reliable <i>in</i></span><i><span style="font-family:;" "=""> </span></i><i><span style="font-family:;" "="">situ</span></i><span style="font-family:;" "=""> station observations for the period between 2012 and 2020 were used for the comparison with CHIRPS satellite data models in the same epoch. Rainfall values within the minimum 5 km and maximum 20 km radii</span><span style="font-family:;" "=""> </span><span style="font-family:;" "="">from the <i>in</i></span><i><span style="font-family:;" "=""> </span></i><i><span style="font-family:;" "="">situ</span></i><span style="font-family:;" "=""> stations were extracted at a 5 km interval from the interpolated <i>in</i></span><i><span style="font-family:;" "=""> </span></i><i><span style="font-family:;" "="">situ</span></i><span style="font-family:;" "=""> station surface and the CHIRPS satellite data model for comparison. Results of the 5 km radius were adopted for the evaluation as it</span><span style="font-family:;" "="">’</span><span style="font-family:;" "="">s closer to the optimal rain gauge coverage of 25 km<sup>2</sup>. They show the R<sup>2</sup> = 0.91, NSE = 0.88, PBias = <span style="white-space:nowrap;"><span style="white-space:nowrap;">-</span></span>0.24 and RSR = 0.35. This attests that the CHIRPS satellite gridded datasets provide a good approximation and simulation of <i>in</i></span><i><span style="font-family:;" "=""> </span></i><i><span style="font-family:;" "="">situ</span></i><span style="font-family:;" "=""> station data with high collinearity and minimum deviation. This tallies with related studies in other regions that have found CHIRPS datasets superior to interpolation surfaces and sparse rain gauge data in the comprehensive estimation of rainfall. With a 0.05<span style="white-space:nowrap;">°</span> * 0.05<span style="white-space:nowrap;">°</span> (Latitude, longitude) spatial resolution, CHIRPS satellite gridded rainfall estimates are therefore able to provide a comprehensive rainfall estimation at a local scale. Essentially these results reward research science in regions like Uganda that have sparse rain gauges networks characterized by incomplete, inconsistent and unreliable data with an empirically researched alternative source of rainfall estimation data. It further provides a platform to scientifically interrogate the rainfall dynamics at a local scale in order to infuse local policy with evidence-based formulation and application.</span><span></span> </p>展开更多
Three coupling coefficients are defined to describe spatiotemporal coupling in ultrashort pulses. With these coupling coefficients, the first-order spatiotemporal couplings of Gaussian pulse and beam are described ana...Three coupling coefficients are defined to describe spatiotemporal coupling in ultrashort pulses. With these coupling coefficients, the first-order spatiotemporal couplings of Gaussian pulse and beam are described analytically. Also, the first-order and the second-order spatiotemporal couplings caused by angular dispersion elements are studied using these coupling coefficients. It can be shown that these coupling coefficients are dimensionless and normalized, and readily indicate the severity of spatiotemporal coupling.展开更多
基金Project supported by 100 Talents Program of Chinese Academy of Sciencesthe National Natural Science Foundation of China(Grant Nos.61475169,61521093,and 11127901)the Youth Innovation Promotion Association of Chinese Academy of Sciences
文摘The spatial chirp generated in the Ti：sapphire multipass amplifier is numerically investigated based on the one- dimensional （1D） and two-dimensional （2D） Frantz-Nodvik equations. The simulation indicates that the spatial chirp is induced by the spatially inhomogeneous gain, and it can be almost eliminated by utilization of proper beam profiles and spot sizes of the signal and pump pulses, for example, the pump pulse has a top-hatted beam profile and the signal pulse has a super-Gaussian beam profile with a relatively larger spot size. In this way, a clear understanding of spatial chirp mechanisms in the Ti：sapphire multipass amplifier is proposed, therefore we can effectively almost eliminate the spatial chirp and improve the beam quality of a high-power Ti：sapphire chirped pulse amplifier system.
基金supported by the National Natural Science Foundation of China (Grant No. 12074329)Nanhu Scholars Program for Young Scholars of Xinyang Normal University。
文摘With a three-dimensional semiclassical ensemble method, we theoretically investigated the nonsequential double ionization of Ar driven by the spatially inhomogeneous few-cycle negatively chirped laser pulses. Our results show that the recollision time window can be precisely controlled within an isolated time interval of several hundred attoseconds, which is useful for understanding the subcycle correlated electron dynamics. More interestingly, the correlated electron momentum distribution (CEMD) exhibits a strong dependence on laser intensity. That is, at lower laser intensity, CEMD is located in the first quadrant. As the laser intensity increases,CEMD shifts almost completely to the second and fourth quadrants, and then gradually to the third quadrant.The underlying physics governing the CEMD's dependence on laser intensity is explained.
文摘<p> <span style="font-family:;" "="">The Ugandan economy is largely dependent on rural-based and rain-fed agriculture. This creates a critical need to understand the rainfall dynamics at the local scale. However, the country has a sternly sparse and unreliable rain gauge network. This research, therefore, set</span><span style="font-family:;" "="">s</span><span style="font-family:;" "=""> out to evaluate the use of </span><span style="font-family:;" "="">the </span><span style="font-family:;" "="">CHIRPS satellite gridded dataset as an alternative rainfall estimate for local modelling of rainfall in Uganda. Complete, continuous and reliable <i>in</i></span><i><span style="font-family:;" "=""> </span></i><i><span style="font-family:;" "="">situ</span></i><span style="font-family:;" "=""> station observations for the period between 2012 and 2020 were used for the comparison with CHIRPS satellite data models in the same epoch. Rainfall values within the minimum 5 km and maximum 20 km radii</span><span style="font-family:;" "=""> </span><span style="font-family:;" "="">from the <i>in</i></span><i><span style="font-family:;" "=""> </span></i><i><span style="font-family:;" "="">situ</span></i><span style="font-family:;" "=""> stations were extracted at a 5 km interval from the interpolated <i>in</i></span><i><span style="font-family:;" "=""> </span></i><i><span style="font-family:;" "="">situ</span></i><span style="font-family:;" "=""> station surface and the CHIRPS satellite data model for comparison. Results of the 5 km radius were adopted for the evaluation as it</span><span style="font-family:;" "="">’</span><span style="font-family:;" "="">s closer to the optimal rain gauge coverage of 25 km<sup>2</sup>. They show the R<sup>2</sup> = 0.91, NSE = 0.88, PBias = <span style="white-space:nowrap;"><span style="white-space:nowrap;">-</span></span>0.24 and RSR = 0.35. This attests that the CHIRPS satellite gridded datasets provide a good approximation and simulation of <i>in</i></span><i><span style="font-family:;" "=""> </span></i><i><span style="font-family:;" "="">situ</span></i><span style="font-family:;" "=""> station data with high collinearity and minimum deviation. This tallies with related studies in other regions that have found CHIRPS datasets superior to interpolation surfaces and sparse rain gauge data in the comprehensive estimation of rainfall. With a 0.05<span style="white-space:nowrap;">°</span> * 0.05<span style="white-space:nowrap;">°</span> (Latitude, longitude) spatial resolution, CHIRPS satellite gridded rainfall estimates are therefore able to provide a comprehensive rainfall estimation at a local scale. Essentially these results reward research science in regions like Uganda that have sparse rain gauges networks characterized by incomplete, inconsistent and unreliable data with an empirically researched alternative source of rainfall estimation data. It further provides a platform to scientifically interrogate the rainfall dynamics at a local scale in order to infuse local policy with evidence-based formulation and application.</span><span></span> </p>
基金supported by the Program for New Century Excellent Talents in University(NCET),China(Grant No.NCET-05-0784)
文摘Three coupling coefficients are defined to describe spatiotemporal coupling in ultrashort pulses. With these coupling coefficients, the first-order spatiotemporal couplings of Gaussian pulse and beam are described analytically. Also, the first-order and the second-order spatiotemporal couplings caused by angular dispersion elements are studied using these coupling coefficients. It can be shown that these coupling coefficients are dimensionless and normalized, and readily indicate the severity of spatiotemporal coupling.
