Strong interactions in multimode random lasers

Unlike conventional lasers, diffusive random lasers (DRLs) have no resonator to trap light and no high-Q resonances to support lasing. Because of this lack of sharp resonances, the DRL has presented a challenge to conventional laser theory. We present a theory able to treat the DRL rigorously and provide results on the lasing spectra, internal fields, and output intensities of DRLs. Typically DRLs are highly multimode lasers, emitting light at a number of wavelengths. We show that the modal interactions through the gain medium in such lasers are extremely strong and lead to a uniformly spaced frequency spectrum, in agreement with recent experimental observations.     

Trapped ions, laser cooling, and better clocks

Ions that are stored in electromagnetic "traps" provid the basis for extremely high resolution spectroscopy. By using lasers, the kinetic energy of the ions can be cooled to millikelvin temperatures, thereby suppressing Doppler frequency shifts. Potential accuracies of frequency standards and clocks based on such experiments are anticipated to be better than one part in 10(15).     

脉冲掺铒波导激光器研究进展

目前发展的用于脉冲掺铒光波导激光器的技术主要有：调Q技术、半导体饱和吸收镜被动锁模技术以及带尾纤的碳纳米管（CNTs）饱和吸收被动锁模技术。对基于调Q技术的波导嫩光器、基于半导体饱和吸收镜被动锁模技术的波导激光器、带尾纤的碳纳米管（CNTs）饱和吸收被动锁模技术的波导激光器的发展现状以及存在的问题进行了分析研究,并针对目前存在的问题,指出了其发展方向。     

Stabilized lasers and precision measurements

This article traces the development of stabilized lasers from the Massachusetts Institute of Technology passive-stabilization experiments of the early 1960's up through the current epoch of highly stabilized helium-neon and carbon dioxide and continuous wave dye lasers. The utility, present performance, and limitations of stabilized lasers as standards of length or frequency for precision measurements are discussed. Examples considered of laser applications to physical measurements of outstanding scientific interest include determination of the speed of light, redefinition of the meter, resolution of the photon recoil-induced spectral doubling, use of optical "Ramsey" interference fringes from ultrahigh-resolution spectroscopy, and two improved tests of special relativity.     

微波陶瓷材料温度系数测试系统研制

基于开路型平行板介质谐振腔工作原理,介绍微波陶瓷材料频率温度系数的测试技术。为提高检测的可靠性与稳定性,缩短测试时间,充分利用微机接口技术和单片机电路组建快速测试系统,包括硬件和软件构成,实现控制测量。该方案对加快研究介质器件的应用作出探索。     

Quartz: extreme preferred orientation produced by annealing

Annealing of samples of flint under high pressure, after hot-working in the beta-quartz stability field, produced an exceedingly strong concentration of c-axes parallel to the direction of compression. A specimen deformed under identical conditions, but not annealed, exhibited a much weaker orientation. The strength of the annealed orientation rivals that of the remarkable "cube texture" produced by annealing some face-centered cubic metals after extreme reduction by rolling.     

Seismic determination of elastic anisotropy and mantle flow

When deformed, many rocks develop anisotropic elastic properties. On many seismic records, a long-period (100 to 250 seconds), "quasi-Love" wave with elliptical polarization arrives slightly after the Love wave but before the Rayleigh wave. Mantle anisotropy is sufficient to explain these observations qualitatively as long as the "fast" axis of symmetry is approximately horizontal. Quasi-Love observations for several propagation paths near Pacific Ocean subduction zones are consistent with either flow variations in the mantle within or beneath subducting plates or variations in the direction of fossil spreading in older parts of the Pacific plate.     

大功率半导体激光阵列远场光强分布研究

针对Bar和Stack两种类型激光器,运用双峰模型,对各个发光单元的光强进行非相干叠加,得出Bar和Stack两种激光器的远场光强模型,并根据此模型模拟出Bar和Stack的远场光强分布。分别定量描述了Bar和Stack光强分布均匀的区域以及开始出现类似单发光单元的双峰分布的位置,并给出了相应的经验计算公式。利用这些公式以及器件数据手册给出的参数即可方便的计算出Bar和Stack的均匀区域以及出现类似单发光单元的双峰分布的位置。理论分析与实验结果基本吻合。可为Bar和Stack在实际应用中设计光学系统以及光束质量评价提供理论依据。     

Direct mapping of nuclear shell effects in the heaviest elements

Quantum-mechanical shell effects are expected to strongly enhance nuclear binding on an "island of stability" of superheavy elements. The predicted center at proton number Z = 114, 120, or 126 and neutron number N = 184 has been substantiated by the recent synthesis of new elements up to Z = 118. However, the location of the center and the extension of the island of stability remain vague. High-precision mass spectrometry allows the direct measurement of nuclear binding energies and thus the determination of the strength of shell effects. Here, we present such measurements for nobelium and lawrencium isotopes, which also pin down the deformed shell gap at N = 152.     

Diode laser--pumped solid-state lasers

Diode laser-pumped solid-state lasers are efficient, compact, all solid-state sources of coherent optical radiation. Major advances in solid-state laser technology have historically been preceded by advances in pumping technology. The helical flash lamps used to pump early ruby lasers were superseded by the linear flash lamp and arc lamp now used to pump neodymium-doped yttrium-aluminum-garnet lasers. The latest advance in pumping technology is the diode laser. Diode laser-pumped neodymium lasers have operated at greater than 10 percent electrical to optical efficiency in a single spatial mode and with linewidths of less than 10 kilohertz. The high spectral power brightness of these lasers has allowed frequency extension by harmonic generation in nonlinear crystals, which has led to green and blue sources of coherent radiation. Diode laser pumping has also been used with ions other than neodymium to produce wavelengths from 946 to 2010 nanometers. In addition, Q-switched operation with kilowatt peak powers and mode-locked operation with 10-picosecond pulse widths have been demonstrated. Progress in diode lasers and diode laser arrays promises all solid-state lasers in which the flash lamp is replaced by diode lasers for average power levels in excess of tens of watts and at a price that is competitive with flash lamp-pumped laser systems. Power levels exceeding 1 kilowatt appear possible within the next 5 years. Potential applications of diode laser-pumped solid-state lasers include coherent radar, global sensing from satellites, medical uses, micromachining, and miniature visible sources for digital optical storage.     

番茄新品种冀番3号的选育

冀番３号番茄是以自交系冀农为母本,１０２为父本配制而成的一代杂种。无限生长类型,生长势强,高抗ＴＭＶ,兼抗疫病。果形园正,平均单果重１８０￣２００ｇ,畸形果少,裂果极轻,品质优良。丰产性突出,产量５０００￣６０００ｋｇ／６６７ｍ＾２。适应性广,适于全国各地春、秋露地及秋延后保护地栽培。现已在河北、云南、山西等省大面积推广,累计推广面积１２００ｈｍ＾２。     

关于O命题换位的再思考

对于直言命题的变形推理，传统上认为0命题不能换位。本文通过欧拉图我们可以证明以全称命题为前提的换质位法推理中0命题是能够换位的。它完全符合传统的直言命题变形推理规则。     

High-speed lightwave transmission in optical fibers

There has been considerable progress in the telecommunications technology based on the transmission of lightwaves through optical fibers. Systems experiments in the 1.55-micrometer band have now demonstrated the capability of transmitting at rates as high as 2 gigabits per second over fiber lengths exceeding 100 kilometers, without the use of repeaters to boost the signal. Elements of this progress are advances in the fabrication of low-loss single-mode fibers, in the spectral control of semiconductor junction lasers assuring single-frequency operation, and in high-speed detectors and receivers.     

油烟机清洁剂对泥鳅胚胎和仔鱼的毒性研究

[目的]研究油烟机清洁剂对水生生物安全性的影响。[方法]以胚胎孵化率、畸形率为指标,以胚胎发育的4个不同时期和仔鱼期为处理时间,研究了油烟机清洁剂对泥鳅胚胎及仔鱼发育的影响。[结果]油烟机清洁剂可诱使泥鳅胚胎孵化率降低、畸形率升高,对胚胎发育具有一定的致畸、致死作用。随着油烟机清洁剂浓度的增加,泥鳅胚胎孵化率逐渐降低,畸形率逐渐升高。尾芽期处理的胚胎孵化率和畸形率明显高于其他时期处理。油烟机清洁剂对泥鳅仔鱼生长的抑制作用不明显,其24h半数致死浓度和安全浓度分别为1.23和0.05ml/L。[结论]油烟机清洁剂对泥鳅有毒,且具有剂量效应。     

MATERIALS SCIENCE: Long-Wavelength Lasers Sniff Out New Uses

Just a few weeks after two physicists won the Nobel Prize for figuring out how to make lasers out of semiconductors, researchers announced that they have made those lasers much more useful. A new technique permits the lasers to shine light in regions of the infrared spectrum previously inaccessible to similar devices. The advance may open the door to cheap devices to sniff explosives and other robotic sensors.     

Modifying the ionosphere with intense radio waves

The ionospheric modification experiments provide an opportunity to better understand the aeronomy of the natural ionosphere and also afford the control of a naturally occurring plasma, which will make possible further progress in plasma physics. The ionospheric modification by powerful radio waves is analogous to studies of laser and microwave heating of laboratory plasmas (20). " Anomalous" reflectivity effects similar to the observed ionospheric attenuation have already been noted in plasmas modulated by microwaves, and anomalous heating may have been observed in plasmas irradiated by lasers. Contacts have now been established between the workers in these diverse areas, which span a wide range of the electromagnetic spectrum. Perhaps ionospheric modification will also be a valuable technique in radio communications.     

ELECTRONIC OPTICS: Organic Lasers Promise New Lease on Light

Many of today's lasers are made from ceramic chips that require expensive clean-room facilities to manufacture, and their color palette is somewhat limited. Researchers have long pinned their hopes on organic materials, which are typically easier and cheaper to process. Now, on page 599, a team reports that they've devised the first electrically powered solid state organic laser, a step that could open the floodgates for novel lasers that are cheaper and that shine in colors inorganics can't match.     

激光对小麦的诱变效果及其在育种上的应用

采用等电聚焦丙烯酰胺凝胶电泳法和微核技术,分析检测了三种激光对小麦L_1代的诱变效应,电冰分析表明:激光确有提高酯酶活性的作用,表现在酯酶带增加、电泳扫描图上反映出峰面扩大且色泽加深;在形态上植株生长健壮;在花粉母细胞分裂间划,微核率比对照增加0.13～1.99％,研究结果还表明,激光能诱发小麦L_1和L_2代性状的变异,对经激光处理后的L_1有促进生长的作用,而且使L_2的部份经济性状产生了变异,如出现的高秆突变率>矮秆突变率,以15 W的CO_2激光处理2分钟的诱变效果最好,我们利用CO_2激光辐射处理小麦干种子,选育出了浙娄3号和浙麦4号新品种。     

Self-mode-locking of quantum cascade lasers with giant ultrafast optical nonlinearities

We report on the generation of picosecond self-mode-locked pulses from midinfrared quantum cascade lasers, at wavelengths within the important molecular fingerprint region. These devices are based on intersubband electron transitions in semiconductor nanostructures, which are characterized by some of the largest optical nonlinearities observed in nature and by picosecond relaxation lifetimes. Our results are interpreted with a model in which one of these nonlinearities, the intensity-dependent refractive index of the lasing transition, creates a nonlinear waveguide where the optical losses decrease with increasing intensity. This favors the generation of ultrashort pulses, because of their larger instantaneous intensity relative to continuous-wave emission.     

Ultrahigh-density nanowire lattices and circuits

We describe a general method for producing ultrahigh-density arrays of aligned metal and semiconductor nanowires and nanowire circuits. The technique is based on translating thin film growth thickness control into planar wire arrays. Nanowires were fabricated with diameters and pitches (center-to-center distances) as small as 8 nanometers and 16 nanometers, respectively. The nanowires have high aspect ratios (up to 10(6)), and the process can be carried out multiple times to produce simple circuits of crossed nanowires with a nanowire junction density in excess of 10(11) per square centimeter. The nanowires can also be used in nanomechanical devices; a high-frequency nanomechanical resonator is demonstrated.