共查询到20条相似文献，搜索用时 46 毫秒
1.
Byer RL 《Science (New York, N.Y.)》1988,239(4841):742-747
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 The helical flash lamps used to pump early ruby lasers were superseded by the linear flash lamp and arc lamp now used to pump neodymium-doped yttrium-aluminum-garnet lasers.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. 相似文献
2.
功率因数校正(PFC)电路作为谐波补偿装置和提高功率因数的有效措施已成为电力电子技术研究的热点问题,且绝大多数PFC采用Boost电路,在中等及以上功率等级时PFC常采用电流连续模式,而功率二极管由于存在反向恢复特性,开关管的开通损耗被大大增加,电磁干扰加重。本文提出了一种新的电容型无源无损缓冲电路,其能够抑制二极管的反向恢复特性,减小开关管的开通损耗,提高PFC的效率。电路结构简单,软开关实现范围大,500W实验样机验证了PFC在半载时效率能提高1.08%。 相似文献
3.
Feng L Ayache M Huang J Xu YL Lu MH Chen YF Fainman Y Scherer A 《Science (New York, N.Y.)》2011,333(6043):729-733
Optical communications and computing require on-chip nonreciprocal light propagation to isolate and stabilize different chip-scale optical components. We have designed and fabricated a metallic-silicon waveguide system in which the optical potential is modulated along the length of the waveguide such that nonreciprocal light propagation is obtained on a silicon photonic chip. Nonreciprocal light transport and one-way photonic mode conversion are demonstrated at the wavelength of 1.55 micrometers in both simulations and experiments. Our system is compatible with conventional complementary metal-oxide-semiconductor processing, providing a way to chip-scale optical isolators for optical communications and computing. 相似文献
4.
Preliminary experiments indicate that tunable Pb(1-x)Sn(x)Te diode lasers will be useful in the identification and sensitive detection of most of the atmospheric pollutant gases. For point-sampling applications, concentrations in the parts-per-billion range should be measurable with very high specificity. For long-range atmospheric transmission techniques, the improved resolution capability and tunability of these diode lasers make them attractive replacements for spectrometers and fixed-frequency laser sources where operation at cryogenic temperatures is not a serious impediment. By using these lasers as tunable local oscillators in the infrared heterodyne configuration, remote passive detection of gases present in smokestack effluent appears possible. Finally, pulsed operation at temperatures available with simple cryogenic coolers permits immediate application to the fast detection of gases present in automobile exhaust and in chemical processing plants. 相似文献
5.
Krupa DJ Wiest MC Shuler MG Laubach M Nicolelis MA 《Science (New York, N.Y.)》2004,304(5679):1989-1992
Ensemble neuronal activity was recorded in each layer of the whisker area of the primary somatosensory cortex (SI) while rats performed a whisker-dependent tactile discrimination task. Comparison of this activity with SI activity evoked by similar passive whisker stimulation revealed fundamental differences in tactile signal processing during active and passive stimulation. Moreover, significant layer-specific functional differences in SI activity were observed during active discrimination. These differences could not be explained solely by variations in ascending thalamocortical input to SI. Instead, these results suggest that top-down influences during active discrimination may alter the overall functional nature of SI as well as layer-specific mechanisms of tactile processing. 相似文献
6.
介绍了采用单一电流传感器检测功率因数校正主电路中电感电流信号的控制方法.该方法可同时控制输入电流波形和输出电压,不需要分别检测输入电压和输出电压.被检测的电感电流主要用在2个方面:一是用于与锯齿波信号相比较去控制输入电流的波形;另一是用于当主开关处于开通或关断状态时,通过对电感电流变化率的处理得出输入和输出电压信号.同传统的APFC相比较,该方法具有以下优点:(1)不再使用耗能的分压电阻器采集信号;(2)自然实现了功率转换级同控制级的电气隔离;(3)不必进行复杂的数字采样和大量计算. 相似文献
7.
Efficient signal communication uses photons. Signal processing, however, uses an optically inactive medium, electrons. Therefore, an interconnection between electronic signal processing and optical communication is required at the integrated circuit level. We demonstrated control of exciton fluxes in an excitonic integrated circuit. The circuit consists of three exciton optoelectronic transistors and performs operations with exciton fluxes, such as directional switching and merging. Photons transform into excitons at the circuit input, and the excitons transform into photons at the circuit output. The exciton flux from the input to the output is controlled by a pattern of the electrode voltages. The direct coupling of photons, used in communication, to excitons, used as the device-operation medium, may lead to the development of efficient exciton-based optoelectronic devices. 相似文献
8.
半导体激光器稳功率电路设计 总被引：4，自引：0，他引：4
半导体激光二极管随着温度的增加，阈值电流提高，输出功率下降。为了使半导体激光二极管输出激光功率稳定，设计了激光二极管稳功率电路。试验结果表明，电路设计合理，输出激光功率稳定，达到了设计要求。 相似文献
9.
Dayan B Parkins AS Aoki T Ostby EP Vahala KJ Kimble HJ 《Science (New York, N.Y.)》2008,319(5866):1062-1065
Beyond traditional nonlinear optics with large numbers of atoms and photons, qualitatively new phenomena arise in a quantum regime of strong interactions between single atoms and photons. By using a microscopic optical resonator, we achieved such interactions and demonstrated a robust, efficient mechanism for the regulated transport of photons one by one. With critical coupling of the input light, a single atom within the resonator dynamically controls the cavity output conditioned on the photon number at the input, thereby functioning as a photon turnstile. We verified the transformation from a Poissonian to a sub-Poissonian photon stream by photon counting measurements of the input and output fields. The results have applications in quantum information science, including for controlled interactions of single light quanta and for scalable quantum processing on atom chips. 相似文献
10.
A p-n junction diode of cubic boron nitride was made by growing an n-type crystal epitaxially on a p-type seed crystal at a pressure of 55 kilobars and a temperature of about 1700 degrees C. A temperature-difference solvent method was used for the crystal growth, and beryllium and silicon were doped as acceptors and donors, respectively. Formation of the p-n junction was clearly confirmed at 1 bar by rectification characteristics and by existence of a space charge layer of the junction as observed by electron beam induced current measurement. This diode operated at 530 degrees C. 相似文献
11.
Photons are excellent information carriers but normally pass through each other without consequence. Engineered interactions between photons would enable applications as varied as quantum information processing and simulation of condensed matter systems. Using an ensemble of cold atoms strongly coupled to an optical cavity, we found that the transmission of light through a medium may be controlled with few photons and even by the electromagnetic vacuum field. The vacuum induces a group delay of 25 nanoseconds on the input optical pulse, corresponding to a light velocity of 1600 meters per second, and a transparency of 40% that increases to 80% when the cavity is filled with 10 photons. This strongly nonlinear effect provides prospects for advanced quantum devices such as photon number-state filters. 相似文献
12.
为了很好地消除电力系统中的谐波，提出了一种动态电力滤波器设计方案，它是在无源电力滤波器基础上，通过反并联晶闸管来控制滤波支路的投切。采用了频谱分析法和电压过零点控制相应的滤波支路投入运行。该动态电力滤波器结构简单、操作简便、造价低廉、维修容易，还具有动态稳定性高、选择性强、与系统谐振几率小、投切瞬间不存在振荡等优点。通过仿真，该动态电力滤波器能够很好地滤除谐波源中的各次谐波。 相似文献
13.
Quantum technologies based on photons will likely require an integrated optics architecture for improved performance, miniaturization, and scalability. We demonstrate high-fidelity silica-on-silicon integrated optical realizations of key quantum photonic circuits, including two-photon quantum interference with a visibility of 94.8 +/- 0.5%; a controlled-NOT gate with an average logical basis fidelity of 94.3 +/- 0.2%; and a path-entangled state of two photons with fidelity of >92%. These results show that it is possible to directly "write" sophisticated photonic quantum circuits onto a silicon chip, which will be of benefit to future quantum technologies based on photons, including information processing, communication, metrology, and lithography, as well as the fundamental science of quantum optics. 相似文献
14.
Lee N Benichi H Takeno Y Takeda S Webb J Huntington E Furusawa A 《Science (New York, N.Y.)》2011,332(6027):330-333
We report on the experimental quantum teleportation of strongly nonclassical wave packets of light. To perform this full quantum operation while preserving and retrieving the fragile nonclassicality of the input state, we have developed a broadband, zero-dispersion teleportation apparatus that works in conjunction with time-resolved state preparation equipment. Our approach brings within experimental reach a whole new set of hybrid protocols involving discrete- and continuous-variable techniques in quantum information processing for optical sciences. 相似文献
15.
基于光纤中的四波混频(FWM)产生高重复频率超短光脉冲的原理,并为抑制光纤中的受激Brillouin散射(SBS),采用非均匀掺杂高SBS阈值非线性光纤,通过FWM对双拍频信号进行整形压缩,实验上获得了100GHz的高重复率超短光脉冲序列,进而分析了入纤功率对输出光脉冲的影响。 相似文献
16.
The microscopic particle motions from the crystal to the disordered state of a dusty plasma with micrometer-sized silicon dioxide particle suspensions in a radio-frequency glow discharge system were studied through an optical microimaging system. Small-amplitude random motion around the lattice sites of the crystal state, relative domain motion with varying boundaries, cooperative hopping in the liquid state, and highly disordered motion with increasing radio-frequency power were observed. Chaotic states with different spatial scales under the coherent and stochastic coupling between dust particles and self-organized background plasma fluctuations were also demonstrated. 相似文献
17.
目前,国内会计师仍采用人工方式进行票据数据录入,完成账目的处理,错误率高且效
率低,针对该问题,本系统开发出一款对发票实现自动化信息识别并报账的软件,实现从数据采
集到报账完成一体的自动化服务。本系统在MATLAB 软件上运行,结合光学识别OCR 引擎
Tesseract 软件实现功能,基础功能包括:票据图像的无线收发、票据图像信息提取处理与识别,自
动生成财务报表等功能。此外,为了提高系统的可靠性,增加了如多段关键信息截取、图像的倾
斜校正、数学形态学处理等技术。 相似文献
18.
二极管双平衡混频器电路分析 总被引：1，自引：0，他引：1
探讨了二极管环形混频电路的工作原理,通过分析和计算,得出最终输出电流的组合频率分量.分析认为,由于二极管特性不配对,变压器中心抽头不对称,各端口之间的隔离是不理想的,总会有极少量功率在各端口之间窜通.提出了解决组合频率干扰问题的3种措施. 相似文献
19.
Visual resolution in humans is nearly equal for vertically and horizontally oriented detail, but for some subjects there is a substantial difference in resolving power for these orientations. Although subjects who exhibit this difference invariably have ocular astigmatism, optical explanations of the effect can be ruled out. Direct evidence has been found for an electrophysiological correlate to the psychophysical finding. Subjects who have reduced resolution for a pattern of a particular orientation also show a decreased evoked potential response elicited by a target of the same orientation. The results are consistent with the hypothesis that a deficiency of specific features in the early visual input can alter the organization of the visual pathways. 相似文献
20.
A cantilever resonant microbeam, laser diodes, and a photodiode have been fabricated on the surface of a gallium arsenide substrate. The microbeam is excited photothermally by light from a laser diode. The vibration is detected with a photodiode as the variation in light output caused by the difference in optical length between the microbeam and another laser diode. A high carrier-to-noise ratio (45 decibels) is achieved with a short (3 micrometers) external cavity length. Such a small distance allows a lensless system, which increases the ease of fabrication. This work could lead to applications in which photomicrodynamic systems are monolithically integrated on a gallium arsenide substrate with surface micromachining technology. 相似文献