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An all fiberized novel sub-ns pulsed fiber laser was presented based on the "figure-of-eight" cavity mode-locking.The output pulse train was directed to pass a fiberized acousto-optic modulator based on first-order diffraction to reduce the pulse repetition rate from 2.78 MHz to 93 kHz by adjustable pulse picking.After the repetition rate decreasing,the peak power of the pulse laser was over 25 kW with the second amplifier,of which slope efficiency was 68.1%.Then the laser was used to excite bismuth doped silica fiber with optimization fiber length of 3m for supercontinuum generation.Finally the obtained laser spanned a spectral range of 1 100~2 200 nm with flatness better than 3 dB.

A gain-switched Yb-doped pulse fiber laser which was periodically pumped by a pulsed Laser Diode(LD) centering at wavelength of 975 nm was reported.The pulsed Yb fiber laser was composed of a piece of Yb doped double cladding gain fiber and a pair of fiber Bragg gratings.Under pump power of 20 W and pulse duration of 2.4 μs at repetition rate of 50 kHz,stable laser pulse trains were obtained at 1 060 nm with pulse duration of 100 ns.The shot energy of every pulse was measured up to 20 μJ.Using this pulsed Yb fiber laser as the seed,a maser-oscillator power amplifier(MOPA) structured high power Yb laser was constructed with pulse energy exceeding 200 μJ.The slope efficiency of the MOPA was about 60%.

Our previous research showed an increasing trend of rainfall in a temperate arid region of China.In this study,to address potential effects of additional rain on carbon emissions of an arid ecosystem,we conducted a field manipulative experiment with five simulated rain addition treatments(four rain addition treatments and one for comparison).Each treatment included four repetitive plots,each with an area of approximately 113 m2,in Dun Huang,Gansu.The design simulated rain increases of 0%(CK),50%,100%,200% and 300% of the long-term(1978—2008) average annual precipitation(40 mm) at the study site.We used the Li-8100 automated soil CO2 flux system in a Nitraria sphaerocarpa community during the growing season,from May to September 2010.Our results showed a linear positive correlation in soil carbon emissions between 09:00—11:00 and 24:00 hours for vegetated and bare soil(bare soil R2=0.31—0.76,P0.001;vegetated soil R2=0.85—0.96,P0.001).The rain increases accelerated vegetated and bare soil respiration in the plots.Compared with the control group,soil carbon emissions of bare soil increased by 8.83,11.03,26.64,31.69 g/m2,and the emissions of vegetated soil increased by 30.02,45.34,98.08,133.90 g/m2 with the 0%(CK),50%,100%,200% and 300% treatments,respectively.Soil carbon emissions of vegetated soil were three times greater than those of bare soil during the growing season,which was statistically significant.There was a significant linear correlation between soil carbon emissions and precipitation during the growing season,in both bare soil and vegetated soil.With a 1 mm increase in rainfall,soil carbon emissions in vegetated and bare soils increased 1.12 g/m2 and 0.27 g/m2,respectively.With a given community cover,every 1 mm rainfall increase produced an additional 0.69 g/m2 of soil carbon emission,relative to the control treatment. We developed a multiple linear regression model for community coverage,precipitation and soil carbon emissions of a community of Nitraria sphaerocarpa,and found that soil carbon emissions of the control group were 2.97—6.55 kg from May to September.During the growing season,when community coverage was eight percent,soil carbon emissions of the community increased by 0.62,2.18,5.30 and 8.42 kg with the 0%(CK),50%,100%,200% and 300% treatments,respectively.With community coverage at nineteen percent,the emissions respectively increased by 1.56,3.12,6.24 and 9.36 kg for those same treatments.For community coverage of thirty-eight percent,the respective emission increases were 2.50,4.06,7.18 and 10.30 kg.This study is important for estimating the ecosystem carbon budget in the arid region of Northwest China with future rainfall increases.

For optical short pulse with high frequency,it is needed to improve the pump power to obtain more shorter pulse;but,as increasing of the pump power,the gain of the amplifier is becoming saturated,and amplified spontaneous emission noise(ASE) is increasing,so signal to noise ratio(SNR) is decreased.A scheme of pulse compression through fiber-optical parametric amplifier and chirp management is proposed.First the pump light is phase modulated after intensity modulation to introduce linear positive chirps,after the parametric progress the frequency chirps of the idler are doubled,so its spectral width is increased,the pulse can be compressed through dispersion compensation medium.The experimental results of 10GHz operation is demonstrated,with 0.5W average pump power and phase modulated pump power,idler pulse is observed with 19ps pulse width.