共查询到20条相似文献，搜索用时 62 毫秒
1.
Shelton RK Ma LS Kapteyn HC Murnane MM Hall JL Ye J 《Science (New York, N.Y.)》2001,293(5533):1286-1289
We generated a coherently synthesized optical pulse from two independent mode-locked femtosecond lasers, providing a route to extend the coherent bandwidth available for ultrafast science. The two separate lasers (one centered at 760 nanometers wavelength, the other at 810 nanometers) are tightly synchronized and phase-locked. Coherence between the two lasers is demonstrated via spectral interferometry and second-order field cross-correlation. Measurements reveal a coherently synthesized pulse that has a temporally narrower second-order autocorrelation width and that exhibits a larger amplitude than the individual laser outputs. This work represents a new and flexible approach to the synthesis of coherent light. 相似文献
2.
Ma LS Bi Z Bartels A Robertsson L Zucco M Windeler RS Wilpers G Oates C Hollberg L Diddams SA 《Science (New York, N.Y.)》2004,303(5665):1843-1845
A femtosecond laser-based optical frequency synthesizer is referenced to an optical standard, and we use it to demonstrate the generation and control of the frequency of electromagnetic fields over 100 terahertz of bandwidth with fractional uncertainties approaching 1 part in 10(19). The reproducibility of this performance is verified by comparison of different types of femtosecond laser-based frequency synthesizers from three laboratories. 相似文献
3.
High rates of volcanic and tectonic activities are inferred from Venus's high surface temperature. The effects of volcanic effluents, gas and dust, on obscuration in the atmosphere are considered. The optical extinction due to particulate matter is estimated from assumed distributions as to particle size and altitude. As few as ten explosive eruptions per annum would cause significant absorption and scattering of visible light. 相似文献
4.
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
5.
Interfering light waves produce an optical interference pattern in any medium that interacts with light. This modulation of some physical parameter of the system acts as a classical holographic grating for optical radiation. When such a grating is produced through interaction of pulsed light waves with an optical transition, a transient grating is formed whose decay is a measure of the relaxation time of the excited state. Transient gratings can be formed in real space or in frequency space depending on the time ordering of the interfering light waves. The two gratings are related by a space-time transformation and contain complementary information on the optical dynamics of a system. The status of a grating can be probed by a delayed third pulse, which diffracts off this grating in a direction determined by the wave vector difference of the interfering light beams. This generalized concept of a transient grating can be used to interpret many picosecond-pulse optical experiments on condensed-phase systems. Examples of some low-temperature experiments will be presented. In principle, many of these experiments could also be performed by using stochastic broad-band excitation. In these nonlinear photon-interference experiments the time resolution is determined by the correlation time of the light source rather than its pulse width. 相似文献
6.
对大兴安岭地区阔叶低质林进行6、10、14、18 m带宽皆伐后,并种植西伯利亚红松(Pinus koraiensis)进行诱导改造,利用LI-8150多通道土壤碳通量自动测量仪测定土壤表面CO2通量,分析不同带宽诱导改造土壤呼吸速率的影响因子。结果表明:不同带宽土壤呼吸速率均高于对照样地,表现为18 m带宽6.51μmol.m-2.s-1>10 m带宽5.33μmol.m-2.s-1>14 m带宽5.26μmol.m-2.s-1>6 m带宽3.53μmol.m-2.s-1>对照样地3.12μmol.m-2.s-1。在Spearman相关性检验中,不同带宽诱导改造后土壤密度与土壤呼吸速率呈现显著负相关性,土壤有机质、半分解层枯落物质量与土壤呼吸速率表现出显著正相关性(p<0.05)。6 m带宽、10 m带宽、14 m带宽、18 m带宽和对照样地的土壤呼吸敏感指数(Q10)值分别为3.72、1.09、2.77、4.31和2.58。随着土壤含水量的升高土壤呼吸速率逐渐升高,但达到一定临界值后土壤呼吸速率呈现出下降的趋势,而不同诱导改造林这一临界值不同。 相似文献
7.
Ultrashort laser pulses have thus far been used in two distinct modes. In the time domain, the pulses have allowed probing and manipulation of dynamics on a subpicosecond time scale. More recently, phase stabilization has produced optical frequency combs with absolute frequency reference across a broad bandwidth. Here we combine these two applications in a spectroscopic study of rubidium atoms. A wide-bandwidth, phase-stabilized femtosecond laser is used to monitor the real-time dynamic evolution of population transfer. Coherent pulse accumulation and quantum interference effects are observed and well modeled by theory. At the same time, the narrow linewidth of individual comb lines permits a precise and efficient determination of the global energy-level structure, providing a direct connection among the optical, terahertz, and radio-frequency domains. The mechanical action of the optical frequency comb on the atomic sample is explored and controlled, leading to precision spectroscopy with an appreciable reduction in systematic errors. 相似文献
8.
Yu N Genevet P Kats MA Aieta F Tetienne JP Capasso F Gaburro Z 《Science (New York, N.Y.)》2011,334(6054):333-337
Conventional optical components rely on gradual phase shifts accumulated during light propagation to shape light beams. New degrees of freedom are attained by introducing abrupt phase changes over the scale of the wavelength. A two-dimensional array of optical resonators with spatially varying phase response and subwavelength separation can imprint such phase discontinuities on propagating light as it traverses the interface between two media. Anomalous reflection and refraction phenomena are observed in this regime in optically thin arrays of metallic antennas on silicon with a linear phase variation along the interface, which are in excellent agreement with generalized laws derived from Fermat's principle. Phase discontinuities provide great flexibility in the design of light beams, as illustrated by the generation of optical vortices through use of planar designer metallic interfaces. 相似文献
9.
The precise manipulation of a propagating wave using phase control is a fundamental building block of optical systems. The wavefront of a light beam propagating across an interface can be modified arbitrarily by introducing abrupt phase changes. We experimentally demonstrated unparalleled wavefront control in a broadband optical wavelength range from 1.0 to 1.9 micrometers. This is accomplished by using an extremely thin plasmonic layer (~λ/50) consisting of an optical nanoantenna array that provides subwavelength phase manipulation on light propagating across the interface. Anomalous light-bending phenomena, including negative angles of refraction and reflection, are observed in the operational wavelength range. 相似文献
10.
研究了啁啾高斯光脉冲信号对带前置放大器光接收机灵敏度的影响,进行了理论分析和数值摸拟,并以常见的G652A光纤为例研究了啁啾、群速度色散、光信号码元速率和高斯光脉冲信号的占空比对光接收机灵敏度恶化量的影响。研究表明,适当选取高斯光脉冲信号的占空比、啁啾、光接收机均衡滤波器输出的升余弦波形滚降因子的值可以提高光接收机灵敏度;群速度色散存在时,占空比的减小反而导致灵敏度恶化量的增加,说明光信号脉冲宽度并非越小越好。适当选取啁啾、群速度色散的参量β2和风以及占空比的值可以使光接收机灵敏度的恶化量降低。该研究结果对光接收机的分析和设计有一定的指导意义。 相似文献
11.
Joiner S 《Science (New York, N.Y.)》2000,290(5498):1907-1908
The unsatiable demand for more bandwidth threatens to lead to the Internet's collapse. In his Perspective, Joiner explains that new optical technologies are the key to resolving both today's "last-mile" bottleneck and future intrasystem bottlenecks. At the core of the new technology lies the vertical cavity surface emitting laser. 相似文献
12.
杨家坚 《上海水产大学学报》2008,17(6)
使用LHRH—A2＋DOM＋PG混合催产剂对从海南引进经池塘驯化养殖5冬龄的海南长臀鲍进行催产,并用日产80i光学显微镜观察胚胎发育过程。取得平均催产率88．9％,平均受精率82．3％,平均孵化率68．7％的效果。成熟的卵子为圆球形、淡黄色、粘性卵。在水温24．8～27．0℃条件下,其受精卵经细胞期、囊胚期、原肠期、体节出现期、器官出现期和出膜前期等多个发育时期孵化出膜,所需时间为82h 15min。拍摄了胚胎发育照片25幅。 相似文献
13.
Although the identity and interactions of signaling proteins have been studied in great detail, the complexity of signaling networks cannot be fully understood without elucidating the timing and location of activity of individual proteins. To do this, one needs a means for detecting and controlling specific signaling events. An attractive approach is to use light, both to report on and control signaling proteins in cells, because light can probe cells in real time with minimal damage. Although optical detection of signaling events has been successful for some time, the development of the means for optical control has accelerated only recently. Of particular interest is the development of chemically engineered proteins that are directly sensitive to light. 相似文献
14.
The diffraction limit of light, which is causd by the loss of evanescent waves in the far field that carry high spatial frequency information, limits the resolution of optical lenses to the order of the wavelength of light. We report experimental demonstration of the optical hyperlens for sub-diffraction-limited imaging in the far field. The device magnifies subwavelength objects by transforming the scattered evanescent waves into propagating waves in an anisotropic medium and projects the high-resolution image at far field. The optical hyperlens opens up possibilities in applications such as real-time biomolecular imaging and nanolithography. 相似文献
15.
By exploiting nonlinear optical effects, a technology of unprecedented flexibility for the production of tunable coherent light has been developed. Referred to as optical parametric generation, it provides sources with spectral coverage extending all the way from the ultraviolet to the mid-infrared, and with temporal coverage extending over all time domains from the femtosecond pulse to the continuous wave. Such sources generate coherent light of outstanding optical quality and are now finding wide-ranging applications. 相似文献
16.
Righini R 《Science (New York, N.Y.)》1993,262(5138):1386-1390
In the optical Kerr effect, the electric field of light incident on a transparent sample induces an anisotropic refractive index, which is measured by its effect on the passage of a second light beam. The advent of lasers powerful enough to generate a measurable effect, and which can be pulsed on femtosecond time scales, has made the optical Kerr effect into a practical technology for investigating the molecular structure and interactions of condensed systems such as pure liquids, liquid solutions, and plastic crystals. 相似文献
17.
Hayatsu R 《Science (New York, N.Y.)》1966,153(3738):859-861
Scattered light produces spurious optical rotations of up to 80 milli degrees in commercial polarimeters. Even larger "rotations," up to 180 milli-degrees, are observed when the sample simultaneously absorbs and scatters light.These effects may account for the optical activity reported in the Orgueil meteorite. 相似文献
18.
Circular dichroism of biological macromolecules 总被引：11，自引：0，他引：11
S Beychok 《Science (New York, N.Y.)》1966,154(754):1288-1299
Circular dichroism, the unequal absorption of right and left circularly polarized light, is a manifestation of optical activity in the vicinity of absorption bands. To the experimental scientist interested in the conformation of macromolecules and in the sensitive response of optical activity to conformational alteration, it offers a relatively new and powerful means of understanding the environment of chromophoric residues. As a tool in the elucidation of electronic spectra, it should be useful to the theoretical scientist in identifying weakly allowed absorption bands as well as in providing rotational parameters which can be compared with the developing theory of optical activity. I have stressed application of circular dichroism, to experimental aspects of protein and nucleic acid conformation in solution. Much is still uncertain in particular quantitative details. However, even these early results shed new light and yield new information on the conformation of these molecules. 相似文献
19.
Mühlschlegel P Eisler HJ Martin OJ Hecht B Pohl DW 《Science (New York, N.Y.)》2005,308(5728):1607-1609
We have fabricated nanometer-scale gold dipole antennas designed to be resonant at optical frequencies. On resonance, strong field enhancement in the antenna feed gap leads to white-light supercontinuum generation. The antenna length at resonance is considerably shorter than one-half the wavelength of the incident light. This is in contradiction to classical antenna theory but in qualitative accordance with computer simulations that take into account the finite metallic conductivity at optical frequencies. Because optical antennas link propagating radiation and confined/enhanced optical fields, they should find applications in optical characterization, manipulation of nanostructures, and optical information processing. 相似文献
20.
Plasmonics provides a route to develop ultracompact optical devices on a chip by using extreme light concentration and the ability to perform simultaneous electrical and optical functions. These properties also make plasmonics an ideal candidate for dynamically controlling nonlinear optical interactions at the nanoscale. We demonstrate electrically tunable harmonic generation of light from a plasmonic nanocavity filled with a nonlinear medium. The metals that define the cavity also serve as electrodes that can generate high direct current electric fields across the nonlinear material. A fundamental wave at 1.56 micrometers was frequency doubled and modulated in intensity by applying a moderate external voltage to the electrodes, yielding a voltage-dependent nonlinear generation with a normalized magnitude of ~7% per volt. 相似文献