微腔中CdSe量子点荧光增强效应

文章主要研究了CdSe量子点微腔结构,微腔结构包括上下分布式布拉格反射镜(DBR),中间的有源层为溶解在聚甲基丙烯酸甲酯(PMMA)中的CdSe胶体量子点.采用传递矩阵法模拟微腔的反射光谱,对实验测试曲线进行较好的拟合.通过测试微腔结构的光致荧光(PL)光谱,其半峰宽(FWHM)由未加入微腔的CdSe量子点样品的27.9 nm,减小到微腔结构的7.5 nm,在微腔中的量子点,由于腔模式的出现,其发光谱的品质因数增加了3.6倍,达到了荧光增强的效果. 关键词： CdSe量子点 微腔效应 荧光增强     

电致发光色纯性增强的硅基有机微腔

报道了硅基有机微腔的电致发光（EL）.该微腔由上半透明金属膜、中心有源多层膜和多孔硅分布Bragg反射镜（PS DBR）组成.半透明金属膜由Ag（２０nm）构成，充当发光器件的负电极和微腔的上反射镜.有源多层膜由Al (1 nm) / LiF(05 nm) /Alq3/Alq3:DCJTB/NPB/CuPc/ITO/SiO2组成，其中的Al/LiF为电子注入层，ITO为正电极，SiO2为使正、负电极电隔离的介质层.该PS DBR是采用设备简单、成本低廉且非常省时的电化学腐蚀法用单晶Si来制备的；该PS 关键词： 电化学腐蚀 电致发光 窄峰发射 硅基有机微腔     

Strong exciton-photon coupling in an organic single crystal microcavity

We demonstrate strong exciton-photon coupling of Frenkel excitons at room temperature in a microcavity composed of a melt grown thin film anthracene single crystal and two distributed Bragg reflectors. Angle-resolved reflectivity and normal incidence photoluminescence under weak excitation are observed. The microcavity spectrum is a function of the anisotropy of the crystalline material and the strong exciton-photon coupling of the excitonic resonances to the cavity photon. The photoluminescence spectrum is found to be completely polarized along the crystal axes.     

On the antiresonances of a microcavity with quarter-wave dielectric mirrors

The amplitude reflectivity spectrum and the associated finesse of a microcavity with quarter-wave dielectric mirrors have been theoretically analysed. Triangular-shaped antiresonances were obtained when the radius of the incident beam was not much larger than a wavelength. This was due to the dispersion caused by high spatial frequency components of the incident beam. The dispersion resulted in an increase of the width of the high-transmission region, and therefore greatly degraded the finesse of the cavity.     

微腔有机电致发光器件的谐振腔反射镜性能

根据微腔原理运用传输矩阵法对构成微腔有机电致发光器件(MOLED)谐振腔的两个反射镜进行模拟计算并比较,可观察到:随金属反射镜的反射率增大,微腔器件的电致发光(PL)谱的半峰全宽(FWHM)逐渐窄化;峰值逐渐蓝移至设计的谐振峰值520nm处;峰值强度和光谱积分强度逐渐增强。结果表明:金属反射镜反射率越大越好。随DBR反射镜的周期数从1增加到9,EL的峰值均为520nm,半峰全宽逐渐窄化,积分强度逐渐减弱;峰值强度由弱增强再减弱,4个周期时峰值强度最大,所以设计微腔器件时,DBR的周期是一项很重要的参数。DBR反射率太大不利于出光,太小微腔效应小。需要根据制作目的和需要进行合理选择。     

Optical characterization of a GaAs/AlGaAs vertical cavity surface emitting quantum well laser structure grown by MOCVD

In this work we report on the characterization and modelling of the reflectivity of a vertical cavity surface emitting quantum well laser (VCSEQWL) grown by MOCVD. The theoretical simulation of the reflectivity was developed for the purpose of designing VCSEQWL cavity multilayer reflectors. Included in the model are the effects of the n = 1 electron/heavy hole (e-hh) and electron/light hole (e-lh) exciton absorptions and the dispersion of the multilayer materials on the cavity mirror reflectivity. Using this model we analysed the influence of systematic deviations of the multilayer thicknesses on the VCSEQWL cavity reflectivity. Good agreement was achieved between the measured and simulated reflectivity if we allowed for systematic deviations in the thicknesses of the epilayers of ± 2.5%. Electroluminescence measurements from the VCSEQWL showed the n = 1 (e-hh) quantum well transition to be matched to the laser cavity resonance. Both calculated and measured results showed that when the n = 1 (e-hh) exciton transition matched the microcavity resonance the exciton absorption was strongly enhanced due to the multiple reflections of the incident light beam in the cavity.     

Polariton thermalization in GaN microcavities in the strong light–matter coupling regime

We discuss the thermalization of the polariton population from a bulk GaN λ/2 microcavity at room temperature. Simultaneous optical measurements of reflectivity and photoluminescence (PL), as well as time resolved measurements, reveal strong light–matter coupling. Transfer matrix theory is used to calculate reflectivity, absorption, and transmission coefficients for the structure. The PL emission is found to be thermalized, despite its very short lifetime, suggesting the existence of very fast energy relaxation channels.     

共轴环光子晶体的缺陷微腔特性

 采用数值计算方法,模拟了共轴环光子晶体缺陷微腔的谐振模式场分布,计算了此微腔的品质因数和功率损耗,并分析其几何参数对谐振特性的影响。以此缺陷微腔为基础构建周期性慢波系统,讨论了该系统的色散特性。结果表明,微腔中能够存在单一的谐振模式,微腔的纵向长度和介质环介电常数对谐振特性影响较大。所构建的慢波系统有较宽的慢波频域,且慢波比曲线较为平坦。增大电子注开孔半径和减小周期长度对于提高工作频率及增加带宽较为有效。     

Temperature dependent polariton emission from strongly coupled organic semiconductor microcavities

We investigated the absorption and photoluminescence (PL) of J-aggregates of a cyanine dye both in a thin film format and when used as the active layer in a strongly-coupled microcavity. We show that as temperature is reduced, the absorption linewidth of the J-aggregates narrows and shifts to higher energy. When the J-aggregate is placed in a microcavity we find that the energy of the polariton modes also shifts to higher energies as temperature is reduced. We compare the intensity of PL emission from the upper and lower branches at resonance as a function of temperature, and find that it can be described by an activation energy of 25 meV. PL emission spectra at resonance also suggest that uncoupled excitons inside the microcavity populate the upper polariton branch states.     

Controllable electromagnetic transmission based on metallic nanoslit with a microcavity

In this paper, we explore the electromagnetic transmission through a vertical metallic nanoslit with a horizontal microcavity. The introduction of microcavity gives rise to the changes of slit transmission spectrum in the number and amplitude of transmission peak and dip, owing to the electromagnetic coupling between slit and microcavity. The transmission through the slit with microcavity strongly depends on whether the isolated slit is in resonance or not, and the microcavity resonance is an additional factor that influences the transmission. The transmission spectrum can be adjusted by changing the opening position of slit, and the slit depth, the width and depth of microcavity. Our results are analysed and discussed from the view of Fano resonance. These results may be of value in tuning electromagnetic wave in subwavelength optics and designing plasmonic devices based on composite metallic nanoslit structures.     

Resonances near the classical separatrix of a weakly deformed circular microcavity

We study localized resonance patterns of a weakly deformed circular dielectric microcavity. The dominant pattern among them is detected when the classical motion of the light is on the separatrix of the effective potential. In this case, the topological shape of the pattern is automatically determined by the refractive index of the microcavity n. Also, the pattern can be interpreted as a linear combination of nearly degenerate eigenstates in the circular dielectric microcavity. Applying this analysis to a spiral-shaped microcavity, we generate quasiscarred patterns for n=2 and n=3.     

Influence of optical confinement and excitonic absorption on strong coupling in a bulk GaN microcavity grown on silicon

We report the optical study of a lambda-thick GaN microcavity grown by molecular beam epitaxy on a silicon substrate. Angle-resolved reflectivity measurements evidence the strong coupling regime at room temperature on the half cavity (without the top mirror), but at low temperature, the high excitonic absorption quenches the optical cavity mode at the excitonic energies. On the whole microcavity, the improved quality factor leads to the observation of the polariton emission whatever the temperature. No bottleneck is observed at 70 K even at low pumping power and large negative detuning. The impact of the optical confinement and the excitonic absorption, studied through reflectivity measurements are accurately reproduced by the transfer-matrix formalism. The optimization of the design in this structure leads to a large Rabi splitting (52 meV) at room temperature.     

Dynamics of a Dipolariton Optical Parametric Oscillator in a Semiconductor Microcavity

The dynamics of dipolariton states in a planar microcavity has been studied upon pumping of a state corresponding to the middle dipolariton branch. It has been shown that, under exact resonance conditions, both periodic and aperiodic regimes of conversion of pump dipolaritons to dipolaritons of idler and signal modes occur. The periodic regime of conversion of signal and idler dipolaritons without involving pump dipolaritons on the middle branch has also been analyzed.     

电极对CuPc/C60双层异质结有机太阳能电池光学性能的影响

采用传输矩阵法的光学模型以及MATLAB软件模拟了电极对CuPc/C₆₀双层异质结有机太阳能电池光学性能的影响。模拟结果表明:当把微腔结构引入到双层异质结电池时,对于入射电极,发现活性层的吸光率主要受其反射相移的影响而非其透射率,并且通过变化入射电极相移调节层到合适厚度可以使活性层吸光率相比于传统器件增加很多;而当把正负折射率交替的光子晶体引入到电池中作为背电极时,发现活性层的吸光率和背电极反射率、反射相移都有很大关系,在获得高反射率的同时可以通过调节背电极厚度从而使活性层在整个吸收光谱内的吸光率大于传统器件。     

镶嵌于多孔硅微腔中8-羟基喹啉铝的窄峰发射

利用浸渍法将8羟基喹啉铝(Alq₃)镶嵌到多孔硅微腔中,制备了多孔硅微腔—Alq₃镶嵌膜,研究了多孔硅微腔对镶嵌其中的Alq₃自发发射的微腔效应,观察到了光谱窄化、发光强度增强等现象。镶嵌于多孔硅微腔中的Alq₃荧光光谱的半峰全宽只有15nm,而非微腔样品,即镶嵌于普通的单层多孔硅中Alq₃荧光谱半峰全宽在85nm以上。并且有微腔时Alq₃发光强度比没有微腔时Alq₃发光强度增强一个数量级。随机改变微腔中Bragg反射镜高折射率层的几何厚度可使高反射区展宽,从而更加有效地抑制了多孔硅本身的发光模,使发光色度更纯,但由于峰值透射率减小,导致共振峰强度有所减小。多孔硅微腔有机镶嵌膜有可能成为进一步发展Alq₃在电致发光器件方面应用的一条新途径。     

Atom-photon cluster as an elementary emitter

The interaction of an atomic ensemble localized in a microcavity with external electromagnetic fields under Raman resonance conditions with an optically forbidden atomic transition involving photons of the microcavity mode has been described in terms of third-order polynomial algebra. It has been shown that atoms and photons localized in the microcavity under these conditions form a united object, an atom-photon cluster, on the states of which the irreducible representations of polynomial algebra are implemented. Classical coherent and quantum broadband electromagnetic fields are considered as external fields. The effective Hamiltonian, effective dipole moment operator, and relaxation operator of the atom-photon cluster are expressed in terms of the generators of polynomial algebra, which is the algebra of the dynamical symmetry of the problem. The developed mathematical technique has been applied to describe the main radiative processes—spontaneous emission and nutation effect—on atom-photon clusters. All of these effects are peculiar and differ from similar phenomena on two-level atoms, but only simple cases of the mentioned radiative processes have been considered.     

Isotropic photonic bandgap in Penrose textured metallic mircocavity

Photonic microcavity has modified photonic modes that have intense localized electric field, which can couple strongly with the embedded emission centers. In this work, we fabricated 2D photonic microcavities with Penrose quasicrystal pattern with 10-fold symmetry. Organic luminescence material tris(8-hydroxyquinoline) aluminum (Alq₃) was embedded into the microcavity and the angle resolved transmission (ART) and photoluminescence (ARPL) spectra of the microcavity were measured. The results showed that the normal Gaussian photoluminescence spectrum of Alq₃ has been strongly modified by the microcavity dispersion characteristic. In addition, omni-directional photonic band gap exists in the microcavity. The higher symmetry of Penrose quasicrystal pattern means that there was minimal difference in the directional dispersion characteristics.     

Coherent response of a semiconductor microcavity in the strong coupling regime

We have studied the coherent dynamics of a semiconductor microcavity by means of interferometric correlation measurements with subpicosecond time resolution in a backscattering geometry. Evidence is brought of the resolution of a homogeneous polariton line in an inhomogeneously broadened exciton system. Surprisingly, photon-like polaritons exhibit an inhomogeneous dephasing. Moreover, we observe an unexpected stationary coherence up to 8 ps for the lower polariton branch close to resonance. All these experimental results are well reproduced within the framework of a linear dispersion theory assuming a coherent superposition of the reflectivity and resonant Rayleigh scattering signals with a well-defined relative phase.     

石英玻璃微球吸收光谱上的结构共振

通过CO2激光器熔融不同直径的熔锥光纤以得到相应直径的石英玻璃微球,利用此微球和熔锥光纤,构造了球微腔耦合系统。实验中利用光腰直径为3.1μm的熔锥光纤与直径为143.1μm的石英玻璃微球进行耦合,通过最大分辨力为1pm的可调谐半导体激光器对该耦合系统进行光谱扫描,发现石英玻璃微球的吸收光谱中出现分立的结构共振峰。利用光学微球腔理论讨论了石英玻璃微球吸收光谱中的结构共振,并用米氏散射理论公式对一阶TE模共振峰的位置以及它们的间隔进行了计算,共振峰位置实验结果与理论结果的误差仅为0.03%,表明实验与计算结果相符。