Laser fabrication of high-aspect-ratio holes and grooves in photoresist by time constant manipulation

We report on the cw-laser fabrication of sharp-edged holes and grooves in organic-dye-sensitized photoresists for g-line or i-line by manipulating its intensity and scanning rate. The laser fabrication is performed to locally control the reaction time constant of the photoresist. By scanning a tightly focused laser focal spot inside the transparent photoresist, various micron/submicron meter structures have been produced based on the reaction time constant depending on the beam intensity. The proposed method is considered to be a cost-effective technique for high-aspect-ratio holes and grooves fabrication.     

Measurements of neutron yields and spatial distributions in U/Pb, Pb and Hg thick targets bombarded by 0.5 and 1.0 GeV protons

Measurements have been carried out on neutron yields and spatial distributions in U/Pb, Pb and Hg thick targets and the surrounding paraffin moderators bombarded by 0.533 and 1.0 GeV protons. CR-39 detectors were deployed on the surfaces of targets and moderators to record the neutrons produced in the targets. The measurements show that:

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Study of initial shock wave in exhausted flow field by use of a Laser Moire Deflectometry instrument

The initial show wave is a non-stationary phenomenon in the initial stage of an exhausted flow field. Its movement characteristic and development process cannot be mastered accurately with the use of contact-type measurement methods, such as pressure and velocity measurements. An experimental study of the shock wave field by use of a Laser Moire Deflectometry instrument is introduced in this paper. The instrument has a large caliber, high sensitivity and high precision. A serial photograph of shock wave field is also presented. The formation mechanism and development trend of the initial shock wave can be drawn from analysis of flow field display photographs.     

Demonstration of massive wavelength-division multiplexing over transoceanic distances by use of dispersion-managed solitons

By combining a special dispersion map that has nearly constant path-average dispersion, a hybrid amplification scheme involving backward-pumped Raman gain, and sliding-frequency guiding filters, we have demonstrated massive wavelength-division multiplexing at 10 Gbits/s per channel, error free (bit-error rate, 相似文献   

Neutron yields upon irradiation of thick targets by ions with energies below 1.75 MeV/Nucleon

The yields of neutrons produced in thick LiF, Be, C, Al, Al₂O₃, and Cu targets irradiated by Li, C, and N ions with energies below 1.75 MeV/nucleon are measured on the DC-60 cyclotron at the Institute of Nuclear Physics, Astana Branch, Kazakhstan. The experimental angular distributions of the neutron yields from the targets are measured and an empirical equation to describe the distributions is proposed. The measured neutron yields are compared with the figures calculated by the LISE++ program. The measured and predicted neutron yields in the reactions coincide to within a factor of 2.     

Reduction of collision-induced timing jitter in dense wavelength-division multiplexing by the use of periodic-group-delay dispersion compensators

We show how replacement of a modest fraction of the usual fiber-based dispersion compensation with a periodic-group-delay dispersion-compensating module can result in a drastic reduction in collision-induced timing jitter in dense wavelength-division multiplexing with dispersion-managed solitons. The principal mechanism here is a correspondingly large reduction in the net path over which a pair of colliding pulses interact.     

Analysis of the impedance mismatch effect in foam-solid targets compressed by laser-driven shock waves

The impedance mismatch effect in a two-layer (low density plastic foam, and solid aluminum, respectively) plane target compressed by a laser driven shock wave is considered. In such targets the ablative pressure generated by absorption of laser light in the foam layer is amplified when crossing the foam-aluminum interface. In this paper an analytical model is developed to evaluate the shock pressure in the aluminum layer as a function of the density and thickness of the foam layer and of the laser parameters. The model is in good agreement with previously published experimental results [A. Benuzzi et al., Phys. Plasmas 5, 2827 (1998)]. Received 20 January 2000 and Received in final form 16 May 2000     

Experimental observation of ionization and shock fronts in foam targets driven by thermal radiation

The behaviours of ionization and shock propagation in radiatively heated material is crucial for the understanding of indirect drive inertial confinement fusion as well as some astrophysics phenomena. In this work, radiation field with a peak temperature of up to 155 eV was generated in a gold cavity heated by four laser beams on the SG-II laser system and was used to irradiate a plastic foam cylinder at one end. The radiatively ablated foam cylinder was then backlighted side-on by x-ray from a laser-irradiated Ti disk. By observing the transmission decrease due to the shock compression of the foam cylinder, the trajectories of shock front were measured, and from the onset of the intense thermal emission from the side of the cylinder, the propagations of the ionization front were also observed on the same shot. The experimental measurements were compared to predictions of the radiation hydrodynamics code Multi-1D and reasonable agreements were found.     

The influence of the state of a compressed thermonuclear substance on the combustion of inertial fusion targets under direct ignition by a short radiation pulse

One-dimensional numerical calculations were performed to study the dependence of conditions for initiating thermonuclear combustion and of the target gain of direct-ignition inertial fusion targets ignited by a short radiation pulse on the initial temperature of a preliminarily compressed fuel and the initial heat energy distribution between plasma electrons and ions in the ignition region (igniter). The igniter parameters at which an effective thermonuclear target explosion with a G ～ 10³ target gain occurred were shown to substantially depend on the initial temperature of the major fuel fraction and the initial heat energy distribution between igniter electrons and ions. The heat energy of the igniter passed a minimum as the size of the igniter decreased. The dependences of these minimum energies on the temperature of the major fuel fraction at various initial energy distributions between igniter electrons and ions were determined. An increase in the temperature of the major fuel fraction was shown to decrease the target gain.     

斜入射激光驱动的冲击波在样品中传播特性的实验研究

在“神光-Ⅱ”高功率激光装置上，利用弯折靶、双台阶靶实验及通过对等离子体喷射状态的实验测量，研究了激光斜入射情况驱动的冲击波传播特性.结果表明，即使在大角度(约45°)斜入射的激光驱动下，靶材料中的冲击波依然是沿着靶面法线方向传播的，并能形成很好的一维正击波. 关键词： 斜入射 冲击波 弯折靶 双台阶靶 激光状态方程     

Passively mode-locked Yb:YAG thin-disk laser with pulse energies exceeding 13 microJ by use of an active multipass geometry

We demonstrate the generation of high-energy picosecond pulses directly from a thin-disk laser oscillator by employing a self-imaging active multipass geometry. Stable single-pulse operation has been obtained with an average output power in excess of 50 W, excluding a cw background of 8%, at a repetition rate of 3.8 MHz. Self-starting passive mode locking was accomplished using a semiconductor saturable absorber mirror. The maximum pulse energy was 13.4 microJ at a pulse duration of 1.36 ps with a time-bandwidth product of 0.34. Single-pass external frequency doubling with a conversion efficiency of 60% yielded >28 W of average power at 515 nm.     

Extreme-ultraviolet spectral purity and magnetic ion debris mitigation by use of low-density tin targets

We investigate the extreme-ultraviolet (EUV) emission from targets that contain tin as an impurity and the advantages of using these targets for ion debris mitigation by use of a magnetic field. The EUV spectral features were characterized by a transmission grating spectrograph. The in-band EUV emission energy was measured with a calorimeter of absolute calibration. The ion flux coming from the plume was measured with a Faraday cup. Our studies indicate that 0.5% Sn density is necessary to obtain a conversion efficiency very close to that of full-density Sn. The use of Sn-doped low-Z targets provides a narrower unresolved transition array and facilitates better control of energetic ions in the presence of a moderate magnetic field of 0.64 T.     

Intense picosecond X-Ray pulses from laser plasmas by use of nanostructured "Velvet" targets

We describe the optical, radiative, and laser-plasma physics of a new type of nanostructured surface especially promising as a very high absorption target for high-peak-power subpicosecond laser-matter interaction. This oriented-nanowire material, irradiated by 1 ps pulses at intensities up to 10(17) W cm(-2), produces picosecond soft x-ray pulses 50x more efficiently than do solid targets. We compare this to "smoke" or metallic clusters, and solid nanogroove-grating surfaces; the "metal-velvet" targets combine the high yield of smoke targets with the brief emission of grating surfaces.     

π−-meson and nucleon yields from light targets irradiated by deuterium and tritium nuclei beams at energies of 1 GeV/nucleon

In this paper, we present a model of calculation with respect to the interactions of high-energy nuclei with matter. Based on this model, we obtain results on energy and angular spectra of the n- and π⁻-particles produced in collisions of deuterium and tritium nuclei at energiesT _d=1 GeV/nucleon with light targets such as Li, Be. We have also estimated the production yields of neutrons and π⁻-mesons in targets of various radii, as well as mean energies of these these particles. Summarizing, we find that the lithium target of radiusR=10−12 cm for which the energy cost ε_π to produce one π⁻-meson is estimated as 6.7 GeV/π for a d-beam and 5.3 GeV/π for a t-beam is the most preferred pion-production target.     

Prompt neutron and gamma-ray yields in fission induced in Pu by resonance neutrons: Existence of the (n, γf) reaction

Fluctuations of the fission neutron multiplicity and prompt γ-ray energy have been measured for resonance neutron induced fission of ²³⁹Pu below 110 eV. An observed anticorrelation between fluctuations of these two parameters is attributed to the role of the (n, γf) reaction.     

Laser cooling of calcium ions by use of ultraviolet laser diodes: significant induction of electron-shelving transitions

Calcium ions are laser cooled in a Paul trap by use of a grating-stabilized UV laser diode. Unusual quantum jumps or fluctuations in the fluorescence signal are observed without application of any shelving lasers. It has become clear that such phenomena can be ascribed to shelving transitions induced by background 393-nm spontaneous photons emitted from the laser medium. Shelving transitions are suppressed by use of an interference filter, and the ions are successfully cooled to crystallization temperature with sufficient reproducibility.     

用光学参量啁啾脉冲放大技术产生TW级激光脉冲系统的最优化设计

用数值模拟的方法,给出了一种适合以纳秒级的高功率钕玻璃激光系统为抽运源的光学参量啁啾脉冲放大(OPCPA)系统的最优化设计.该系统主要由一级LBO预放大器和一级LBO主放大器组成.数值模拟结果表明该系统能够把纳焦级能量的飞秒脉冲放大到焦级,从而产生几十个太瓦(1012W)的脉冲输出.这一结果为进一步利用OPCPA技术放大飞秒脉冲产生拍瓦(1015W)的超短超强激光脉冲输出奠定了基础,从而为强场科学研究提供崭新的技术手段.