Two-Dimensional Visualization of Fluorescence Lifetimes by use of a Picosecond Laser and a Streak Camera

Two-dimensional distributions of the effective lifetime of the fluorescence emission induced by short-pulsed laser radiation are obtained from two-dimensional images recorded with a streak camera and a charge-coupled device by means of a separation algorithm method (SAM). In theory, the best response with respect to noise is obtained for lifetimes corresponding to a range of pixels of 5-50 in the CCD, that is, 5-50 ps at the fastest streak speed. In experiments the SAM is compared with pure time-resolved measurements, and it is used for two-dimensional lifetime evaluation. The laser-pulse duration is 25 ps, and the lower limit of the lifetime resolution as used in the experiments is estimated to be 200-250 ps. The results demonstrate the possibility of performing pattern recognition independently of the relative distribution of emission intensity between regions of different fluorescence lifetimes. The technique is demonstrated for static objects but can in principle be extended to nonstationary objects if two detectors are used.     

A Coplanar Waveguide with a Gallium Arsenide Substrate for an Electro-Optic Sampling System with a Bandwidth Over 110 GHz

Measurement Techniques - The problem of the measurement of the parameters of picosecond electric pulses with bandwidth greater than 110 GHz was examined. In order to measure the parameters of the...     

通过晶格失配调节有盖层张应变Ge量子点的光电特性

利用Ge与不同衬底形成的不同晶格失配度来调节有盖层的张应变Ge量子点的光电特性。通过有限元方法模拟并获得张应变Ge量子点内的应变分布,而后通过形变势理论和有效质量近似计算得到量子点的电子结构。与无盖层张应变Ge量子点相比,有盖层Ge量子点能保持更大的应变量。另外,随着量子点尺寸和晶格失配度的增大,导带Γ谷与导带L谷的能量差缩减,最终使Ge转变为直接带隙材料。直接带隙能量随着量子点尺寸的增大而减小。该研究结果表明张应变Ge量子点是制备包含激光器在内的Si基光源的理想材料,在未来光电子应用中有巨大潜力。     

Picosecond Laser Surface Texturing of a Stavax Steel Substrate for Wettability Control

In this investigation, a picosecond laser was employed to fabricate surface textures on a Stavax steel substrate, which is a key material for mold fabrication in the manufacturing of various polymer products. Three main types of surface textures were fabricated on a Stavax steel substrate: periodic ripples, a two-scale hierarchical two-dimensional array of micro-bumps, and a micro-pits array with nano-ripples. The wettability of the laser-textured Stavax steel surface was converted from its original hydrophilicity into hydrophobicity and even super-hydrophobicity after exposure to air. The results clearly show that this super-hydrophobicity is mainly due to the surface textures. The ultrafast laser-induced catalytic effect may play a secondary role in modifying the surface chemistry so as to lower the surface energy. The laser-induced surface textures on the metal mold substrates were then replicated onto polypropylene substrates via the polymer injection molding process. The surface wettability of the molded polypropylene was found to be changed from the original hydrophilicity to super-hydrophobicity. This developed process holds the potential to improve the performance of fabricated plastic products in terms of wettability control and easy cleaning.     

Frequency Tuning and Chirping of a Pulsed CO2 Laser by an Intracavity Prism

Abstract

Based on results of TEA-CO₂ laser-frequency tuning by an intracavity dispersive prism, the feasibility of CO₂ laser-frequency chirping by a nonlinear intracavity prism or due to self-bending effects is discussed. The proposed scheme is shown to be superior to other nonlinear optics methods for CO₂ laser-frequency chirping.     

Principles of Dye Laser Operation and Dye Laser Tuning Methods

Organic dye lasers have proved to be a high-intensity source of monochromatic radiation that can be tuned to any desired wavelength in the visible range of the spectrum. In this contribution the basic principles of dye laser operation are treated within the model of a suitably modified four-level laser, described in the rate equation approach. The tuning methods based on dispersion by prisms, diffraction by gratings, interferometric effects and polarization effects are discussed. In addition, examples of dye lasers, which are rapidly tunable or which emit simultaneously two or more wavelengths, and some interesting properties of ring lasers are presented.     

High-Contrast Spatial Light Modulator by use of the Electroabsorption and the Electro-Optic Effects in a GaAs Single Crystal

A new spatial light modulator that uses the electroabsorption and the electro-optic effects in a GaAs single crystal is proposed. The device has the same structure as a Pockels readout optical modulator and can be operated at a frame rate higher than 500 Hz. When the electroabsorption and the electro-optic effects are combined, the dynamic range (contrast ratio) becomes larger than that which results when either effect is used singly. It was experimentally confirmed that the modulator has a high contrast ratio (greater than 2000:1), high sensitivity, and consequently large gamma characteristics.     

Picosecond soliton transmission by use of concatenated gain-distributed nonlinear amplifying fiber loop mirrors

Stable picosecond soliton transmission is demonstrated numerically by use of concatenated gain-distributed nonlinear amplifying fiber loop mirrors (NALMs). We show that, as compared with previous soliton transmission schemes that use conventional NALMs or nonlinear optical loop mirror and amplifier combinations, the present scheme permits a significant increase of loop-mirror (amplifier) spacing. The broad switching window of the present device and the high-quality pulses switched from it provide a reasonable stability range for soliton transmission. We also show that a soliton self-frequency shift can be suppressed by the gain-dispersion effect in the amplifying fiber loop and that soliton-soliton interactions can be partially reduced by using lowly dispersive transmission fibers.     

Picosecond Diode-Pumped Laser System with 9.3-W Average Power and 2.3-mJ Pulse Energy

We describe a diode-pumped Nd:YAG laser that is suitable for micromachining applications and is capable of generating 2.3-mJ pulses at a 4-kHz pulse repetition frequency. The output pulse duration is 20.5 ps. The system is based on a Nd:YAG regenerative amplifier with a novel four-pass postamplifier. The postamplifier incorporates birefringent depolarization compensation and simultaneously prevents parasitic laser oscillation by use of a nonreciprocal beam path. These output pulse energies are achieved without the use of chirped pulse amplification.     

Characterization of Diffraction Gratings by use of a Tabletop Soft-X-Ray Laser

We have demonstrated the use of a high-repetition-rate 46.9-nm tabletop laser to characterize diffraction gratings designed for grazing-incidence operation in the soft-x-ray spectral region. The efficiencies for various diffraction orders were measured as a function of angle of incidence and compared with the results of model simulations. This measurement technique provides benchmarks with which to improve electromagnetic codes used in the design of soft-x-ray diffraction gratings. The results illustrate the potential of compact tabletop soft-x-ray lasers for use as a new tool for characterization of short-wavelength optics at the manufacturer's site.     

用于激光加工工艺的脉冲抽样器的设计

在激光加工技术中，就激光打孔而言，制造出规则的序列脉冲是进行高精度打孔的关键。文章介绍了用于对驻波腔腔长进行扫描的脉冲抽样器的设计及制作，利用我们制作的脉冲抽样器对压电陶瓷堆进行高频调制，从而达到扫描激光器谐振腔腔长的目的。此脉冲抽样器在脉冲激光加工工艺，特别是激光打孔技术中有非常实用的价值。此项工作为激光打标工艺作了相应的探索和准备。     

Generation of Picosecond Pulses by Lasers with Distributed Feedback at a Wavelength of 1064 nm

Technical Physics Letters - The mode of generation of picosecond optical pulses in the spectral range near 1064 nm by semiconductor lasers with distributed feedback and active region based on an...     

Picosecond semiconductor lasers with a multisection saturable absorber, fabricated by heavy ion implantation

A method of implanting high-energy heavy ions across the emitter layer of a semiconductor laser has been developed to create distributed regions of ultrafast saturable absorber integrated into the cavity of a quantum-well laser. This method was used to fabricate picosecond laser diodes having high average powers and to demonstrate colliding-pulse mode-locking of a diode laser with a multisection saturable absorber. Pis’ma Zh. Tekh. Fiz. 25, 4–9 (July 12, 1999)     

Signal Recovery in Sinusoid-Crossing Sampling by use of the Minimum-Negativity Constraint

High-frequency components that are lost when a signal s(x) of bandwidth W is low-pass filtered in sinusoid-crossing sampling are recovered by use of the minimum-negativity constraint. The lost high-frequency components are recovered from the information that is available in the Fourier spectrum, which is computed directly from locations of intersections {x(i)} between s(x) and the reference sinusoid r(x) = A cos(2pif(r)x), where the index i = 1, 2, ..., 2M = 2Tf(r), and T is the sampling period. Low-pass filtering occurs when f(r) < W/2. If ?s(x)? 相似文献   

Tuning the Structural and Optoelectronic Properties of Cs2AgBiBr6 Double-Perovskite Single Crystals through Alkali-Metal Substitution

Lead-free double perovskites have great potential as stable and nontoxic optoelectronic materials. Recently, Cs₂AgBiBr₆ has emerged as a promising material, with suboptimal photon-to-charge carrier conversion efficiency, yet well suited for high-energy photon-detection applications. Here, the optoelectronic and structural properties of pure Cs₂AgBiBr₆ and alkali-metal-substituted (Cs_1−xY_x)₂AgBiBr₆ (Y: Rb⁺, K⁺, Na⁺; x = 0.02) single crystals are investigated. Strikingly, alkali-substitution entails a tunability to the material system in its response to X-rays and structural properties that is most strongly revealed in Rb-substituted compounds whose X-ray sensitivity outperforms other double-perovskite-based devices reported. While the fundamental nature and magnitude of the bandgap remains unchanged, the alkali-substituted materials exhibit a threefold boost in their fundamental carrier recombination lifetime at room temperature. Moreover, an enhanced electron–acoustic phonon scattering is found compared to Cs₂AgBiBr₆. The study thus paves the way for employing cation substitution to tune the properties of double perovskites toward a new material platform for optoelectronics.     

非线性光学活性分子的线性电光效应

报道了反射型电光调制法研究６种偶氮化合物的线性电光效应,分析了给体－受体强度、掺杂浓度对线性电光系数的影响。结果表明,掺杂偶氮化合物４－「２－羟乙基苯甲氨基」－４－硝基偶氮苯的极化聚合物薄膜具有较强的线性电光效应,其线性电光系数随参杂浓度的增大而增大。     

Efficient High-Gain Laser Amplification from a Low-Gain Amplifier by use of Self-Imaging Multipass Geometry

We characterize a self-imaging multipass amplifier scheme that provides both high extraction efficiency and overall gain. A diode-pumped slab amplifier with a single-pass small-signal gain of 2.5 is used in a 16-pass mode to amplify an input pulse from 50 muJ to 50 mJ, extracting approximately 22% of the stored energy. A stimulated Brillouin-scattering phase-conjugate mirror provides isolation from amplified spontaneous emission, prevents gain depletion, and also ensures good beam quality. The system can be operated from 10 Hz to in excess of 450 Hz, with modest changes in the beam quality and energy. The scheme has the potential to be scaled to higher-energy and higher-power systems.     

Utilization of the Yellow Component of a Copper-Vapor Laser for Extending the Tuning Range of a Rhodamine 6G Dye Laser by Use of an Additional Dye in a Novel Coupled Resonator Scheme

We demonstrate the use of both 510.6- and 578.2-nm components and the extension of the tuning range of a Rhodamine 6G dye laser in a novel coupled resonator scheme. Rhodamine 6G is pumped by 510.6-nm light in one resonator and Sulforhodamine B is pumped by 578.2 nm in the other. The spectral tuning range of 564-609 nm of the Rhodamine 6G laser is extended up to 640 nm. A two-mirror arrangement ensures continuous tuning across the spectral ranges of the two dyes by rotation of a single plane mirror.     

Estimating Productive Work by Work Sampling with a Preassigned Relative Error

This article discusses a two-stage sampling procedure with a preassigned relative precision for estimating the percent of time spent in an activity of work when little information is available about the actual population percentages beforehand. Only a minimum number of observations will be taken. A table is included to aid in the sample size computations.