利用共焦显微成像系统实现磷光寿命时域测量

在光路中加入斩波器，将共焦显微成像系统中Ar^ 激光器产生的连续光转换为脉冲光，实现对样品的脉冲激发。共焦成像系统以灰度值同时记录了激发光和样品发射磷光的强度变化信息。通过对磷光强度衰减的时间分辨分析，实现对磷光寿命的测量。利用此系统成功地实现了对置于不同环境中的磷光探针氧卟啉（Oxy-Phor R2）衰减寿命的测量。     

单分子的双光子激发光漂白速率

研究了多种条件下的光漂白几率与激发光强度间的定量依赖关系。利用MRC1024多光子激发显微系统和单光子计数技术,测量了单个若丹明B（RhB）分子在不同强度光激发时的双光子激发（TPE）和光漂白寿命。实验结果表明：单个RhB分子和TPE光漂白寿命与激发光强度倒数的平方成正比,亦即光漂白速率与荧光基团分子处于激发态的几率成线性依赖关系,该结果与单光子激发（1PE）时的光漂白结果相同,但是却不同于多分子TPE光漂白的实验结果。     

Lamb波驱动器的最佳激励波形选择

采用高斯窗、海明窗和汉宁窗调制正弦脉冲信号得到不同循环次数的激励波形,分别激励压电式Lamb波驱动器产生Lamb波;引入品质因数(Q)分析信号的频带和频域内强度分布,研究不同窗函数抑制Lamb波频散的效果.实验结果表明,对于相同循环次数不同窗函数调制的激励波形中,经汉宁窗调制的激励信号产生的Lamb波Q值高,频带窄;对于相同窗函数调制的激励波形,随着循环次数的增加,Q值增大.实际应用时可用汉宁窗调制并根据传播距离确定循环次数得到Lamb波最佳激励波形.     

Pure Organic Room Temperature Phosphorescence from Unique Micelle‐Assisted Assembly of Nanocrystals in Water

Pure organic room temperature phosphorescence (RTP) is highly preferable because of its long lifetime and potential applications. However, these kinds of materials are still very scarce due to the weak spin–orbit coupling between singlet and triplet states and easily nonradiative decay of the excited states. Achieving room temperature phosphorescence under visible light excitation is particularly challenging in aqueous solution. Herein, a micelle‐assisted assembling strategy has been developed to realize pure organic RTP in water by using donor–acceptor molecules. A visible‐light responsive long‐lived RTP in water with a lifetime more than 3 ms is obtained by the prepared nanocrystals. However, the same molecules show no RTP as rigid bulk crystals. Spectroscopic studies, single‐crystal structure analysis, X‐ray diffraction patterns, and density functional theory calculations reveal that the intermolecular interactions, heavy atom effect, and the molecular packing way play critical role to the long‐lived RTP character for the assembled nanocrystals in water and thermally activated delayed fluorescence for crystals in solid.     

Coherent self-heterodyne Brillouin OTDR for measurement ofBrillouin frequency shift distribution in optical fibers

Time domain reflectometry of spontaneously Brillouin scattered lightwaves in a single-mode optical fiber is demonstrated with a coherent self-heterodyne detection system employing a recently proposed frequency translator, a DFB laser diode, and erbium-doped fiber amplifiers. Since the probe pulse frequency is up-converted by the translator by an amount approximately equal to the Brillouin frequency shift, the self-heterodyne beat frequency can be reduced to a sufficiently low frequency in the IF band. The system enables one-end measurement of the Brillouin frequency shift distribution in optical fibers with a single way dynamic range (SWDR) of 16 dB and a frequency resolution of 5 MHz for a spatial resolution of 100 m     

All‐Organic,Temporally Pure White Afterglow in Amorphous Films Using Complementary Blue and Greenish‐Yellow Ultralong Room Temperature Phosphors

Organic molecules exhibiting afterglow emission (lifetime longer than 0.1 s) under ambient conditions have sparked tremendous attention in recent years as a sustainable energy source with potential applications in displays, lighting, and bioimaging. However, white afterglow organic materials with color purity during the entire period of delayed emission, after the cessation of excitation source, are yet to be achieved due to the different excited state lifetimes of its primary or complementary components. Herein, a remarkable, ambient “temporally pure white afterglow,” which lasts for over 7 s, by coorganizing complementary blue and greenish‐yellow organic room temperature phosphors with similar ultralong lifetimes and efficiency, in an amorphous polymer film is demonstrated. One of the most efficient blue afterglow room temperature phosphors is also reported, with an ultralong lifetime up to 2.26 s and maximum quantum efficiency of 36.8%, from purely organic triazatruxenes en route to the realization of this white afterglow. Further, broad and complementary absorption features of the coorganized phosphors in the visible region facilitates an excitation‐dependent dynamic color‐tuning of the afterglow from sky‐blue to greenish‐yellow.     

Projecting interconnect electromigration lifetime for arbitrarycurrent waveforms

A vacancy-relaxation model is proposed. It predicts the DC lifetime, pulse DC (arbitrary unidirectional waveform) lifetime, pure AC lifetime, and AC-plus-DC-bias lifetime for all waveforms and all frequencies above 1 kHz. The predictions are verified by experiments and significantly raise the projected lifetimes beyond the widely assumed A_dc T/J_rms^m. The pure AC lifetimes of aluminum interconnect are experimentally found to be more than 10³ times larger than DC lifetime for the same current density. In addition, AC stress lifetimes are observed to follow the same dependences on current magnitude and temperature, for T<300°C, as the DC stress lifetime     

飞秒激光作用下啁啾镜膜层内损伤相关动力学

光学元器件的激光损伤问题,一直以来都困扰着超强超短激光系统的进一步发展。飞秒激光领域,激光脉冲引起的光学器件损伤主要由材料的本征特性决定。光学材料内的多光子电离、雪崩电离、导带电子弛豫等一系列非线性过程,与材料的激光损伤过程密切相关。利用泵浦探测技术,采用中心波长为800 nm,重复频率1 kHz的飞秒激光脉冲,对Nb2O5/SiO2啁啾镜介质膜的内部与飞秒激光损伤相关的超快动力学进行了研究。发现强的泵浦光脉冲辐照结束后飞秒乃至几十皮秒的范围内,啁啾镜对探测光的反射率有一定程度的下降。反射率降低的主要原因是泵浦光在介质膜的Nb2O5层内激发的大量的自由电子对探测光吸收所致,且该过程对激光诱导损伤过程起主导作用。通过反射率的变化,对其介质膜内导带电子弛豫过程进行探究,测定得到其衰减寿命,分别为1.31、6.88、22.34 ps。     

Electromigration performance of electroless platedcopper/Pd-silicide metallization

The electromigration reliability of Cu interconnects has been studied under DC, pulse-DC, and bipolar current stressing conditions. Electroless plating was used to selectively deposit Cu in oxide trenches by using Pd silicide as a catalytic layer at the bottom of the trenches to initiate copper deposition. The DC and pulse-DC lifetimes of Cu are found to be about two orders of magnitude longer than that of Al-2%Si at 275°C, and about four orders of magnitude longer than that of Al-2%Si when extrapolated to room temperature. On the other hand, Cu AC lifetimes are found to be comparable to the AC lifetimes of Al-2%Si. The pulse-DC lifetime of copper interconnects follows the similar frequency and duty factor dependence as aluminium and the prediction of the vacancy relaxation model     

Aging studies of PBGA solder joints reflowed at different conveyorspeeds

In this paper, the shear cycle fatigue properties of plastic ball grid array (PBGA) assemblies' solder joints reflowed with three different profiles, and aged at 125°C for four, nine, 16, 25, and 36 days are studied. The profiles were devised to have the same "heating factor," which was defined as the integral of the measured temperature above the liquidus (183°C) with respect to dwell time in the reflow profile, but to have different conveyor speeds. The effects of conveyor speed on the solder joint (nonaged and aged) fatigue lifetimes were investigated. It was found hat with increasing the conveyor speed the solder joint shear fatigue lifetime could be improved substantially. Also, the shear fatigue lifetimes of aged solder joints decreased with increasing aging time and variation in fatigue lifetimes increased for faster conveyor speed. SEM and optical micrographs show that faster cooling rate caused a rougher interface of solder/IMC and less crystallization microstructure in solder joints. Rougher interface solder joints have a longer nonaged fatigue life. The thickness of IMC increases with increasing aging time and the growth rate for solder with faster cooling rate was larger. SEM cross section views reveal that cracks initiated at the acute position near the solder pad, then propagated along the interface of the bulk solder/IMC layer. Thicker IMC layers deteriorated fatigue life, so the fatigue lifetime variation of aged solder joints with fast cooling rate was larger     

Impedance characteristics of double-hetero structure laser diodes

The effects of the onset of lasing on the I-V characteristics, the impedance characteristics and the light modulation characteristics of laser diodes have been discussed by introducing the rate equations which involve carrier diffusion process in the active layer interacting with the radiation field intensity. The static I-V characteristics exhibit a kink at lasing threshold current, reflecting the decrease of effective lifetime of carriers. Effective carrier lifetimes decrease with increasing light intensity, which results in a steep attenuation of injected carrier density in the active region. The impedance and light modulation characteristics are obtained in the small signal approximation. The small signal light modulation characteristics depend strongly on whether the laser diode is excited by the constant current modulation or the constant voltage modulation. The impedance is changed drastically by the onset of lasing and exhibits a resonance which coincides exactly with the optical modulation resonance frequency.     

Low-profile helical array antenna fed from a radial waveguide

A low-profile array antenna composed of two-turn 4° pitch angle helices is designed for a frequency band of 11.7 GHz to 12.0 GHz. The feed wire of each helix is inserted into a radial waveguide through a small hole and excited by a traveling wave flowing in the transverse electromagnetic mode between the two parallel plates of the waveguide. The measured aperture efficiency shows a maximum value of 77% for a beam radiated in the normal direction and 69% for a 30° beam tilt     

Temperature dependent optical properties of self-organized InAs/GaAs quantum dots

We report photoluminescence (PL), time-resolved PL, and PL excitation experiments on InAs/GaAs quantum dots (QDs) of different size as a function of temperature. The results indicate that both the inhomogeneous properties of the ensemble and the intrinsic properties of single QDs are important in understanding the temperature-dependence of the optical properties. With increasing temperature, excitons are shown to assume a local equilibrium distribution between the localized QD states, whereas the formation of a position-independent Fermi-level is prevented by carrier-loss to the barrier dominating thermally stimulated lateral carrier transfer. The carrier capture rate is found to decrease with increasing temperature and, at room temperature, long escape-limited ground state lifetimes of some 10 ps are estimated. PL spectra excited resonantly in the ground state transition show matching ground state absorption and emission, indicating the intrinsic nature of exciton recombination in the QDs. Finally, the PL excitation spectra are shown to reveal size-selectively the QD absorption, demonstrating the quantum-size effect of the excited state splitting.     

Electromigration characteristics of copper interconnects

The electromigration characteristics of electroless plated copper interconnects have been investigated under DC and time-varying current stressing. A scheme for selected electroless Cu plating by using 150-Å Co as the seeding layer is reported. The Cu DC and pulse-DC lifetimes are found to be one and two orders of magnitude longer than that of Al-4% Cu/TiW and Al-2% Si interconnects at 275°C, and the extracted Cu lifetime at 75°C is about three and five orders of magnitude longer than that of Al-4% Cu/TiW and Al-2% Si, respectively. As previously reported for Al metallization, the Cu bipolar lifetimes were found to be orders of magnitude longer than their DC lifetimes under the same peak stressing current density because of the partial recovery of electromigration damage during the opposing phases of bipolar stressing     

Spectroscopic study of Ga-doped Ge under uniaxial pressure

To identify the optical transitions responsible for the excitation of long-wavelength stimulated emission in uniaxially compressed Ga-doped Ge, the optical absorption and photoconductivity spectra of the material were investigated at a wide range of pressures in directions [111] and [001]. The dependence of the valence band splitting between the light-and heavy-hole subbands in Ge as a function of the applied pressure was found. As determined from this dependence, the deformation potential constants for the valence band appeared to be less than the presently accepted values. It is shown that, as pressure increases, some of the excited states of the Ga impurity levels reach the light-hole band, enter it, and remain close to its edge (the resonant states). It is possible that a population inversion of these resonant states gives rise to the excitation of stimulated emission at a photon energy of about 10 meV. No specific features confirming the existence of resonant impurity states near the edge of the heavy-hole band were found in the spectra.     

High‐Performance Dibenzoheteraborin‐Based Thermally Activated Delayed Fluorescence Emitters: Molecular Architectonics for Concurrently Achieving Narrowband Emission and Efficient Triplet–Singlet Spin Conversion

Thermally activated delayed fluorescence (TADF) materials, which enable the full harvesting of singlet and triplet excited states for light emission, are expected as the third‐generation emitters for organic light‐emitting diodes (OLEDs), superseding the conventional fluorescence and phosphorescence materials. High photoluminescence quantum yield (Φ_PL), narrow‐band emission (or high color purity), and short delayed fluorescence lifetime are all strongly desired for practical applications. However, to date, no rational design strategy of TADF emitters is established to fulfill these requirements. Here, an epoch‐making design strategy is proposed for producing high‐performance TADF emitters that concurrently exhibiting high Φ_PL values close to 100%, narrow emission bandwidths, and short emission lifetimes of ≈1 µs, with a fast reverse intersystem crossing rate of over 10⁶ s^?1. A new family of TADF emitters based on dibenzoheteraborins is introduced, which enable both doped and non‐doped TADF‐OLEDs to achieve markedly high external electroluminescence quantum efficiencies, exceeding 20%, and negligible efficiency roll‐offs at a practical high luminance. Systematic photophysical and theoretical investigations and device evaluations for these dibenzoheteraborin‐based TADF emitters are reported here.     

Optical thermometry through infrared excited upconversionfluorescence emission in Er3+- and Er3+-Yb3+-doped chalcogenide glasses

Optical thermometry based upon infrared excited upconversion fluorescence emission in Er³⁺- and Er³⁺-Yb³⁺ - doped Ga₂S₃-La₂O₃ chalcogenide glasses excited at 1.54 and 1.06 μm, respectively, is presented. Temperature sensing in the region of 20°C-220°C with 0.3°C accuracy using excitation powers readily obtainable from commercially available semiconductor lasers was achieved. The temperature sensing approach is independent of fluctuations in excitation intensity and transmission and requires a simple and low-cost signal detection and processing system. The results also indicate that the glassy host material plays a major role in the performance of the sensing system     

High-power ultralow-chirp 10-Gb/s electroabsorption modulator integrated laser with ultrashort photocarrier lifetime

A high-power, ultralow-chirp electroabsorption modulator (EAM) integrated with a distributed-feedback laser diode (EML) having ultrashort lifetime of photogenerated holes in the EAM quantum-well (QW) structure is reported for the first time. A shallow QW structure having a small valence band offset to enhance the sweepout of photogenerated holes was employed as EAM absorption layer. The measured hole lifetimes were 7-11 ps, and the measured frequency chirp (/spl alpha/-parameter) was low or negative at low EAM reverse bias voltages even under high optical output power conditions. Successful 10-Gb/s 80-km normal-dispersion single-mode fiber transmission (chromatic dispersion D=1600 ps/nm) and the record average fiber optical output power (P/sub f/) of +5.3 dBm were achieved at 25/spl deg/C. In addition, semicooled operation of EML at enhanced bit rates has been demonstrated for application in small-form-factor protocol-agnostic optical transceivers. A 10.7-Gb/s 1600-ps/nm transmission was achieved at 45/spl deg/C and P/sub f/=+3.0 dBm.     

Optical bandwidth considerations in p-i-n multiple quantum-wellmodulators

We investigate the optical bandwidth of p-i(multiple quantum well [MQW])-n modulators employing various MQW designs. The optical bandwidth translates directly into an operating temperature range due to the shift of the band gap with temperature. We find that although greater maximum modulation may be obtained with narrow (~90 Å) quantum wells operating below the band edge (absorption increases with field), uniform large performance may be obtained over a larger bandwidth using wider (~110 Å) quantum wells operating at the exciton (absorption decreases with field). We obtain a usable bandwidth of 7.7 nm, which translates into a operating temperature range of 27°C