Ultrashort light pulses

Experimental techniques are now available for the generation of repetitive and single coherent optical pulses of extremely short time duration and high peak power. These pulses should find extensive application in basic and applied research. Additional shortening of optical pulse durations can be obtained by means of the stimulated Raman effect, second-harmonic generation, or amplification with nonlinear laser amplifiers.     

Electrically controlled nonlinear generation of light with plasmonics

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.     

Resonant optical antennas

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.     

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.     

Parametric Generation of Tunable Light from Continuous-Wave to Femtosecond Pulses

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.     

Optical frequency synthesis and comparison with uncertainty at the 10(-19) level

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.     

基于光外差技术的毫米波ROF系统的研究与仿真

毫米波的产生是ROF系统的技术关键和难点,光外差法是光生毫米波的主要方法之一.介绍了ROF系统的工作原理,给出了ROF系统中光外差法产生毫米波的方案,通过OPTISYSTEM软件仿真实现,并进行了性能分析,经证实,该方案可行且有效.     

Physics and device applications of optical microcavities

Optical microcavities are resonators that have at least one dimension on the order of a single optical wavelength. These structures enable one to control the optical emission properties of materials placed inside them. They can, for example, modify the spatial distribution of radiation power, change the spectral width of the emitted light, and enhance or suppress the spontaneous emission rate. In addition to being attractive for studying the fundamental physics of the interaction between materials and vacuum field fluctuations, optical microcavities hold technological promise for constructing novel kinds of light-emitting devices. One of their most dramatic potential features is thresholdless lasing. In this way and others, controlled spontaneous emission is expected to play a key role in a new generation of optical devices.     

Measurement of ultrafast phenomena in the femtosecond time domain

Considerable progress has taken place in the generation and application of ultrashort optical pulses. The methods and techniques for extending time-resolved measurements into the femtosecond (10(-15) second) time domain are described, and recent applications and fertile areas for investigation with femtosecond pulses are discussed.     

Light propagation with phase discontinuities: generalized laws of reflection and refraction

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.     

Frontiers in Ultrashort Pulse Generation: Pushing the Limits in Linear and Nonlinear Optics

Optical pulses in the 5-femtosecond range are produced by a variety of methods. Although different in technical detail, each method relies on the same three key components: spectral broadening due to the nonlinear optical Kerr effect, dispersion control, and ultrabroadband amplification. The state of the art of ultrashort pulse generation is reviewed with a focus on direct laser oscillator schemes.     

Microresonator-based optical frequency combs

The series of precisely spaced, sharp spectral lines that form an optical frequency comb is enabling unprecedented measurement capabilities and new applications in a wide range of topics that include precision spectroscopy, atomic clocks, ultracold gases, and molecular fingerprinting. A new optical frequency comb generation principle has emerged that uses parametric frequency conversion in high resonance quality factor (Q) microresonators. This approach provides access to high repetition rates in the range of 10 to 1000 gigahertz through compact, chip-scale integration, permitting an increased number of comb applications, such as in astronomy, microwave photonics, or telecommunications. We review this emerging area and discuss opportunities that it presents for novel technologies as well as for fundamental science.     

Plasmonics: merging photonics and electronics at nanoscale dimensions

Electronic circuits provide us with the ability to control the transport and storage of electrons. However, the performance of electronic circuits is now becoming rather limited when digital information needs to be sent from one point to another. Photonics offers an effective solution to this problem by implementing optical communication systems based on optical fibers and photonic circuits. Unfortunately, the micrometer-scale bulky components of photonics have limited the integration of these components into electronic chips, which are now measured in nanometers. Surface plasmon-based circuits, which merge electronics and photonics at the nanoscale, may offer a solution to this size-compatibility problem. Here we review the current status and future prospects of plasmonics in various applications including plasmonic chips, light generation, and nanolithography.     

The most distant known galaxies

Ever since the proposal of the idea of an expanding universe more than 50 years ago, each generation of investigators has found that some current theory could be (marginally) tested by the properties of the most distant known galaxies. There has consequently been a continuing effort to identify very remote objects, especially to confront theories of the evolution of galaxies (since galaxies are seen as they were at prior epochs) and to confront cosmological theories (which make predictions about the overall dynamics of the expansion of the universe). These theories have yet to be definitively tested, but a new generation of optical telescopes and detectors provides hope for significant progress during this decade.     

Combination active optical and passive thermal infrared sensor for low-level airborne crop sensing

An integrated active optical, and passive thermal infrared sensing system was deployed on a low-level aircraft (50 m AGL) to record and map the simple ratio (SR) index and canopy temperature of a 230 ha cotton field. The SR map was found to closely resemble that created by a RapidEye satellite image, and the canopy temperature map yielded values consistent with on-ground measurements. The fact that both the SR and temperature measurements were spatially coincident facilitated the rapid and convenient generation of a direct correlation plot between the two parameters. The scatterplot exhibited the typical reflectance index-temperature profile generated by previous workers using complex analytical techniques and satellite imagery. This sensor offers a convenient and viable alternative to other forms of optical and thermal remote sensing for those interested in plant and soil moisture investigations using the ‘reflectance index-temperature’ space concept.     

光生微波／毫米波系统中信号控制研究

提出了一种基于单模光纤FP腔的光生微波／毫米波技术中的输出信号控制方法,得到了输出信号数目与外加应力之间的解析表达式。利用波长为1550.337nm的连续激光,经过100MHz的RF信号调制后入射单模光纤FP腔,得到了频率为1．25GHz微波信号序列的波形图。通过适当调节所施加的外力,可得到从微波到毫米波的光生信号。     

Stilbazolium-MPS3 Nanocomposites with Large Second-Order Optical Nonlinearity and Permanent Magnetization

Intercalated layered materials comprising an organic dye and inorganic MPS(3) [where M is either the manganese ion (Mn(2+)) or the cadmium ion (Cd(2+))] phases have been prepared. The intercalation process induces a spontaneous poling, giving rise to an efficiency of 750 times that of urea in second-harmonic generation for the cadmium derivative. In addition, the manganese derivative displays a permanent magnetization below 40 kelvin. Thus, these materials exhibit both a large optical nonlinearity and magnetic ordering.     

植食性昆虫产卵寄主选择影响因素 及机制的研究进展

昆虫产卵行为在昆虫与寄主的协同进化中起着重要作用,而母代产卵偏好性和子代生长发育情况的关系是植食性昆虫与寄主植物协同进化研究的核心.文章综述了寄主种类、环境丰富度、寄主生长发育状况和寄主被同种其他个体的利用程度等对植食性昆虫产卵寄主选择的影响,以及嗅觉、视觉和触觉在植食性昆虫产卵寄主选择过程中的作用机制.提出今后应从昆虫视觉生态学和听觉生态学两个角度深入研究植食性昆虫的产卵行为,尤其是加强植食性昆虫与环境中光信号间的联系及如何利用光信号进行寄主定位、 植食性昆虫产卵行为过程中是否利用听器进行声波测探定位产卵寄主及不同波段声音对植食性昆虫产卵行为的影响等研究,为研究害虫行为调控措施开拓新思路.     

基于演化加密的二维码生成技术及在农产品质量安全溯源系统中的应用

二维码技术作为一种电子标签技术,是以计算机和光电技术发展为基础的一项综合性科学技术,是信息采集、输入的重要方法和手段。二维码技术在物流、生产自动化、电子商务各领域被广泛应用的同时,产生了一系列的安全问题。基于演化加密技术,对传统的二维码生成算法进行改进,以提高二维码的防伪性能。并将其在农产品质量安全溯源系统中进行应用,结果表明改进的算法可以进一步提高二维码的安全性。     

Spatiotemporal coherent control of lattice vibrational waves

We achieved automated optical control over coherent lattice responses that were both time- and position-dependent across macroscopic length scales. In our experiments, spatiotemporal femtosecond pulse shaping was used to generate excitation light fields that were directed toward distinct regions of crystalline samples, producing terahertz-frequency lattice vibrational waves that emanated outward from their multiple origins at lightlike speeds. Interferences among the waves resulted in fully specified far-field responses, including tilted, focusing, or amplified wavefronts. Generation and coherent amplification of terahertz traveling waves and terahertz phased-array generation also were demonstrated.