The femtosecond electron diffraction (FED) is a unique method for the study of the changes of complex molecular
structures, and has been specifically applied in the investigations of transient-optics, opto-physics, crystallography,
and other fields. The FED system designed by the present group, consists of a 35nm Ag photocathode evaporated on
an ultraviolet glass, an anode with a 0.1mm aperture, two pairs of deflection plate for the deflection of electron beams
in X and Y directions, and the Y deflection plate can be used as a scanning plate while measuring the pulse width of
electron beams, the double MCPs detector for the enhancing and detecting of electron image. The magnetic lens was
used for the focusing of the electron beams, and the focal length is 125mm. The distance between the object(the
photocathode) and the image(the sample) is 503mm, and the size of electron beams is smaller than 17microns after
focusing, the convergence angle is of -0.075~0.075°, and the temporal resolution is better than 350fs.
We have constructed two kinds of table-top femtosecond terawatt (TW) Ti:sapphire laser systems based on the chirped-pulse
amplification (CPA). With a compact design using only two-stage amplifiers, output energies of 36mJ and 640mJ at 10hz
repetition rates were obtained with recompressed pulse duration of 25 fs, and 31 fs respectively, corresponding to peak
powers of about 1.4 TW and 20 TW. The total pump energy for the last stage is 260 mJ and 2.8 J at wavelength of 532 nm.
These results represent a significant efficiency in amplification and a compact configuration in size. By using an adaptive
optical system to correct the wave-front distortion of the 20TW laser. we further demonstrated the improvement of beam
quality br higher focusable laser intensity.
Two independent femtosecond Ti:sapphire lasers are synchronized by using a new passive synchronization design. By
enhancing the intracavity cross-phase modulation (XPM), stable synchronization operation of remaining for more than 24
hours with a timing jitter of 0.4fs was demonstrated; the tolerance of cavity length mismatch is larger than 10 micrometers.
Plasma emission or ablation from laser-irradiated targets shows very complicated properties. One novelty was observed at irradiation of neodymium glass laser pulses of ps duration and TW power if there was a very strong suppression of prepulses by a contrast ratio of about 108 until 100 ps before the main pulse arrived. The emitted ion maximum energy was more than 50 times below the values observed in all the comparable numerous experiments. The other anomaly is that the number of the fast ions did not change when the laser intensity varied by a factor 30. This permitted a separation of the usual effects of self-focusing and permitted an analysis fully based on simplified plane geometry as a skin layer interaction mechanism. The consequence is that plasma blocks are accelerated by the nonlinear (ponderomotive) force with ion current densities above 1010 A/cm2. This provides basically new aspects for laser fusion using uncompressed solid DT fuel and a new kind of x-ray laser process may be possible.
This paper presents a routing and wavelength assignment for survivability (RWAS) algorithm in optical networks. The attentions of most previous RWA algorithms focus on traffic balance, blocking performance, and network resource utilization, which are key performances of optical networks. However, with the development of DWDM systems and the increase of traffics in optical network, services survivability and network survivability must be paid much more attentions to. RWAS considers services survivability while routing and assigning wavelength(s) for a set of connections, which perhaps has not better resources utilization and blocking performances, but assures that as many service connections as possible can be restored in the current network in the case of any single link failure.
With the emergence of optical cross-connects (OXCs) and optical add/drop multiplexers (OADMs), all-optical networks
and a new layer named as optical layer are emerging. Although the number of available wavelength per fiber and the
bandwidth per wavelength are all becoming larger, the total bandwidth per fiber is limited. So for a network operator,
pre-allocating minimum spare capacity in an optical network under the advanced connection demands to meet to
survivability requirements is needed. In this paper, the above problem can be formulized as an ILP model, in which
different survivability requirements of connections are considered jointly. The solution to this problem has an advantage
over the result of the separate allocation problem, i.e., allocating resources for service connections and protection!
restoration connections are performed separately.
A Ne-like TCE (transient collisional excitation) x-ray laser at 19.6 nm (J equals 0 implied by 1, 3p implied by 3s) was investigated numerically using a sophistic hydrodynamic code for a 100-micrometers thick Ge planar target irradiated by a nano- second prepulse followed by a picosecond main optical laser pulse. The simulations indicate that for a given peak intensity, the main pulse has an optimal duration to generate the maximum effective gain. An effective gain as high as 200 cm-1 was obtained for the optimized drive pulse configuration.
Effects of laser polarization were studied on behaviors of fast electrons produced from an aluminum target irradiated by obliquely incident laser pulses at 8x1015 W/cm2. Jet emission of outgoing fast electrons collimated in the polarization direction was observed for the s-polarized laser irradiation, whereas for the p-polarized irradiation, very directional emission of outgoing fast electrons was found close to the normal direction of the target. The behaviors of in-going fast electrons into the target for s- and p-polarized irradiation were also investigated by observing x-ray Bremsstrahlung radiation at the backside of the target.
One distributed restoration algorithm used to protect optical transport networks against network failures is proposed in the paper. The algorithm takes advantage of the existing IP protocols, and therefore it can restore the affected traffic in the distributed and efficiently manner. By carrying the wavelength availability information in protocol data unit, the algorithm can reserve the required capacities as well as search the restoration routing.
One novel scheme for routing optical supervisory channels adhering to optical cross-connect (OXC) is developed in this paper. Beginning with the definition of the new frame to carry the optical channel (OCH) layer overheads, the proposed scheme processes the overhead associated the individual optical channel, which is carried by optical supervisory channel (OSC), in the similar way as the message-oriented data communication channel (DCC) in OSC. Therefore, all OCH-specified information carried by OSC can be routed by a uniform manner.
Optical Add/Drop Multiplexer (OADM) is an important network element. In the ring architecture, OADM can be introduced to make efficient use of network capacity, network protection, wavelength routing and many more good features. In this paper, an OADM with high performance realized by us is demonstrated. The key technical problem , solving method and design rule for the OADM are given. The experiment results of long distance transmission by use of the OADM are illuminated by some figure . It shows that the OADM realized by us is advanced, practical, reliable, and applied in China Advanced Info-Optical Network (CAINONet).
One FBG-MZI-based component and one mediator are proposed in this paper. The proposed OADM building module consists of one FBG-based MZI module and one reconfigurable module, and it can add/drop or pass-by the specified wavelength. OADM created by concatenating the proposed modules, owns wavelength modularity, and can add-drop and pass-by any specified wavelengths. The mediator is one simplified 4 x 4 optical switch matrix. It can be used to interconnect multiple OADM modules to build one OXC with multiple ports.
In this paper, one novel scheme for evaluating EDFA gain spectrum is introduced. In this scheme, one can determine the EDFA gain spectrum by adjusting one tunable F-P filter (TF) and one tunable attenuator (TA) embedded in the loop-locked configuration (LLC).
The behaviors of hot electrons in femtosecond laser-plasma interaction have been studied systematically under laser irradiance of 5 X 1015 Wcm-2micrometers 2. A very directional jet emission of hot electrons with energies above 170 keV has been observed in the normal direction to the target surface. The angular distribution of the jet emission of hot electrons has been found to be dependent on the energy of hot electrons. By measuring the Faraday rotation angle of the backscattered emission, a magnetic field in the axial direction has been detected for the first time. The maximum value of the magnetic field was estimated to be as high as 1.76 +/- 0.7 Mgauss at such a modest irradiance. It is believed that this axial magnetic field is generated by the dynamo effect in the laser-plasma interaction.
Intense lasing at 18.9, 20.3 and 28.5 nm from nickel-like molybdenum, niobium and neon-like chromium ions has been observed by using two 200 ps laser pulses with a total energy of 50 J at 1.053 micrometers from XingGuang II laser facility. This shows the possibility of extending nickel- like and neon-like x-ray lasing in low-Z elements and paves the way towards small scale x-ray lasers for applications at university laboratories. A comparison has been made of performance of the neon-like chromium soft x-ray lasing at 28.5 nm driven by a double 900 ps pulse at 6 TW(DOT)cm-2, with that driven by a double 200 ps pulse at similar irradiance. The double 200 ps pulse has been found to be more efficient to drive the neon-like x-ray lasing.