氧化铋薄膜用于蓝光可录存储的研究

利用直流磁控溅射法在不同氧氩分压比条件下制备了BiOx薄膜。通过对薄膜在蓝光作用前后的反射率对比度变化的研究发现，氧氩分压比为50％时制备的薄膜具有最佳的光学对比度。利用X射线衍射仪(XRD)、X光电子能谱(XPS)和光谱仪研究了薄膜热处理前后的结构和光谱性质的变化。研究结果表明薄膜光学性质变化主要由薄膜中氧化铋的相变引起。蓝光静态测试结果显示氧氩分压比为50％条件下制备的BiOx薄膜具有很好好的记录敏感度，在11mW的记录功率和800ns的记录脉宽条件下，得到了52％的反射率对比度。此外，BiOx薄膜表现出了非常好的读出稳定性。

A Q-swicthed all-solid-state single-longitudinal-mode laser with adjustable pulse-width and high repetition rate

A single-longitudinal-mode (SLM) laser-diode pumped Nd: YAG laser with adjustable pulse width is developed by using the techniques of pre-lasing and changing polarization of birefingent crystal. The Q-switching voltage is triggered by the peak of the pre-lasing pulse to achieve the higher stability of output pulse energy. The output energy of more than 1 mJ is obtained with output energy stability of 3% (rms) at 100 Hz. The pulse-width can be adjusted from 30 ns to 300 ns by changing the Q-switching voltage. The probability of putting out single-longitudinal-mode pulses is almost 100%. The laser can be run over four hours continually without mode hopping.

Drift distance survey in direct plasma injection scheme for high current beam production

In a laser ion source, plasma drift distance is one of the most important design parameters. Ion current density and beam pulse width are defined by plasma drift distance between a laser target and beam extraction position. In direct plasma injection scheme, which uses a laser ion source and a radio frequency quadrupole linac, we can apply relatively higher electric field at beam extraction due to the unique shape of a positively biased electrode. However, when we aim at very high current acceleration such as several tens of milliamperes, we observed mismatched beam extraction conditions. We tested three different ion current at ion extraction region by changing plasma drift distance to study better extraction condition. In this experiment, C6+ beam was accelerated. We confirmed that matching condition can be improved by controlling plasma drift distance.

Parasitic lasing suppression in high gain femtosecond petawatt Ti: sapphire amplifier

New parasitic lasing suppression techniques are developed and high gain amplification is demonstrated in a petawatt level Ti:sapphire amplifier based on the chirped pulse amplification (CPA) scheme. Cladding the large aperture Ti: sapphire with refractive-index matched liquid doped with absorber suppresses the transverse lasing. The acousto-optic programmable dispersive filter (AOPDF) is used to realize side-lobe suppression in the temporal profile of the compressed pulse. The 800 nm laser output with peak power of 0.89 PW and pulse width of 29.0 fs is demonstrated. (c) 2007 Optical Society of America.

输出高重复频率脉冲列的全固态激光器

报道了利用声光振幅调制锁模的方法，在激光二极管端面抽运Nd：YVO4激光器上获得320MHz高重复频率脉冲列的实验结果。实验采用平一平腔结构，腔长452mm，耦合输出镜透过率为3．6％。所用声光介质为熔融石英晶体，以铌酸锂作换能器，在驱动功率4．5W时，对1064nm波长衍射效率为50，相应的调制深度为0．31。在最佳锁模状态下，激光二极管抽运功率为3．5W，此时激光平均输出功率为15mw。示波器记录脉冲宽度680ps，实测光束质量因子M^2小于1．5。并在实验基础上对激光器工作的稳定性进行了分析，结果表

Diode-pumped passively q-switched Nd : YAG ceramic laser with a Cr4+: YAG crystal-satiable absorber

Transparent polycrystalline Nd:YAG ceramics were fabricated by solid-state reactive sintering a mixture of commercial Al2O3,Y2O3, and Nd2O3 powders. The powders were mixed in ethanol and doped with 0.5 wt% tetraethoxysilane, dried, and pressed. Pressed samples were sintered at 1750 degrees C in vacuum. Transparent fully dense samples with average grain sizes of 10 mu m were obtained. The 1 at.% Nd:YAG ceramic was used to research passively Q-switched laser output with a Cr4+:YAG crystal as a saturable absorber. An average output power of 94 mW with a pulse width of 50 ns was obtained when the incident pump power was 750 mW. The slope efficiency was 13%. The pulse energy is 5 mu J, and the peak power is about 100 W.

Passively mode-locked YVO4/Nd : YVO4 composite crystal laser with a semiconductor saturable absorber as a high reflector

A passively mode-locked diode end-pumped YVO4/Nd:YVO4 composite crystal laser with a five-mirror folded cavity was first demonstrated in this paper by using a low temperature semiconductor saturable absorber mirror grown by metal organic chemical vapor deposition. Both the Q-switching and continuous-wave mode locking operation were realized experimentally. A stable averaged output power of 10.15 W with pulse width of about 11.2-ps at a repetition rate of 113 MHz was obtained, and the optical-to-optical efficiency of 43% was achieved.

基于DSP的永磁同步电机的控制设计与实现

介绍了采用TMS320LF2407A芯片实现对永磁同步电机(PMSM)的设计与控制,讨论了空间矢量脉宽调制(sVPWM)控制方法,并给出了控制系统的硬件设计和软件实现。试验结果表明该系统具有较好的跟踪性能,稳态精度较高;TMS320LF2407A作为DSP控制器24x系列的新成员,是电机数字化控制的升级产品。

梯度补偿法控温晶体的高功率绿光激光器

研究了平均功率超过30 W的稳定高效全固态绿光激光器,分析得出影响全固态腔内倍频激光器倍频效率和输出稳定性的主要因素是倍频晶体局部温升造成的相位失配和热透镜效应,采用温度梯度补偿控温法对大尺寸倍频晶体进行温度控制,降低激光器工作中倍频晶体内外温度梯度从而有效地克服因晶体局部温升造成的倍频相位匹配角失配和热透镜效应。采用三条60 W的半导体激光二极管阵列板条侧面抽运Nd:YAG激光增益介质棒,采用声光调Q,平凹直腔和腔内倍频结构配合温度梯度补偿控温法对大尺寸倍频晶体进行温度控制,得到了稳定高效的532 nm

High-power and low-threshold-current-density GaAs/AlGaAs quantum cascade lasers

We report on the realization of GaAs/AlGaAs quantum cascade lasers with an emission wavelength of 9.1 mu m above the liquid nitrogen temperature. With optimal current injection window and ridge width of 24 and 60 mu m respectively, a peak output power more than 500 mW is achieved in pulsed mode operation. A low threshold current density J(th) = 2.6 kA/cm(2) gives the devices good lasing characteristics. In a drive frequency of 1 kHz, the laser operates up to 20% duty cycle.

Generation of the high efficiency high peak-power femtosecond blue optical pulse

The analysis and calculation of the compensation for the phase mismatch of the frequency-doubling using the frequency space chirp introduced from prisms are made. The result shows that suitable lens can compensate the phase mismatch in a certain extent resulting from wide femtosecond spectrum when the spectrum is space chirped. By means of this method, the experiment of second harmonic generation is carried out using a home-made femtosecond KLM Ti:sapphire laser and BBO crystal. The conversion efficiency of SHG is 63 %. The average output power of blue light is 320 mW. The central wavelength is 420 nm. The spectrum bandwidth is 5.5 nm. It can sustain the pulse width of 33.6 fs. The tuning range of blue light is 404-420 nm,when the femtosecond Ti:sapphire optical pulse is tuned using the prisms in the cavity.

Control of Mean and Fluctuating Forces on a Circular Cylinder at High Reynolds Numbers

A narrow strip is used to control mean and fluctuating forces on a circular cylinder at Reynolds numbers from 2.0 x 10(4) to 1.0 x 10(5). The axes of the strip and cylinder are parallel. The control parameters are strip width ratio and strip position characterized by angle of attack and distance from the cylinder. Wind tunnel tests show that the vortex shedding from both sides of the cylinder can be suppressed, and mean drag and fluctuating lift on the cylinder can be reduced if the strip is installed in an effective zone downstream of the cylinder. A phenomenon of mono-side vortex shedding is found. The strip-induced local changes of velocity profiles in the near wake of the cylinder are measured, and the relation between base suction and peak value in the power spectrum of fluctuating lift is studied. The control mechanism is then discussed from different points of view.

Single attosecond pulse generation in He+ by controlling the instant ionization rate using attosecond pulse trains combined with an intense laser pulse

High-order harmonics and single attosecond pulse generation by using an infrared laser pulse combined with attosecond pulse trains (APT) interacting with He+ have been investigated. We show that the ionization for different instant time intervals can be controlled by altering the time delay between the APT and the infrared pulse. Consequently, APT can be used as a tool to control the efficiency of high-order harmonics emitted at different times. By choosing appropriate APT and time delay, the driving pulse width for single attosecond pulse generation can be extended up to six optical cycles. (c) 2007 Optical Society of America.

Generation of 1.5-12 ns width-tunable 532 nm pulses by adopting laser-induced plasma shutter technique

The pulse-shaping technique has found widespread applications in nonlinear optics and material processing. Experimental research on laser-induced plasma shutter to control the 532 nm pulse width is conducted. The impacts of the total pulse output energy on pulse compression are investigated, and a useful conclusion can be drawn that there exists an optimal value of pulse energy at which the shortest output pulse of 3.23 ns can be obtained without a device for delay-time. Once the device for delay-time is employed to change the optical differences between two laser paths, the pulse width can be further shortened to 1.51 ns. In short, the 1.5-12 ns width-tunable 532 nm laser pulses have been obtained by adopting the laser-induced plasma shutter technique. (C) 2007 Elsevier GmbH. All rights reserved.