Widely tunable amplified spontaneous emission of Pyrromethene-650-doped nematic liquid crystal

We study amplified spontaneous emission of Pyrromethene-650-doped nematic liquid crystal deposited onto quartz and glass substrates. We prepare samples with different dye-doped concentrations pumped with a Nd:YAG laser at 532 nm. With an applied electric field, a tuning range of the amplified spontaneous emission of more than 20 nm was realized in each sample due to changing the effective refractive index of the nematic-liquid-crystal layer caused by the reorientation of nematic-liquid-crystal molecules. We show that there exist a threshold voltage and a saturation voltage for all the samples. With the increase in the dye-doped concentration, the peak wavelength of the amplified spontaneous emission has a red shift of about several nanometers.     

LDS dye-doped zirconia-organically modified silicate distributed feedback planar waveguide lasers

LDS dye-doped pure zirconia and zirconia-organically modified silicate (ORMOSIL) thin film waveguides were prepared on glass substrates by a low-temperature sol–gel technique. The absorption, fluorescence and amplified spontaneous emission properties of the waveguides were investigated. Near infrared distributed feedback laser action was induced in the LDS dye-doped zirconia-ORMOSIL waveguides. Tunable narrow linewidth lasing output from 670 up to 930 nm in a transmission grating geometry was realized in the zirconia-ORMOSIL films.     

Amplified spontaneous emission in neat films of arylene-vinylene polymers

Amplified spontaneous emission (travelling-wave lasing) was achieved for a set of 18 poly(2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylene-vinylene) (MEH-PPV) related arylene-vinylene copolymers, a part of which substituted with additional phenyl groups at the vinyl double bond. Wave-guiding neat thin films on glass substrates were used. The samples were transversally pumped with single second harmonic pulses of a mode-locked ruby laser (wavelength 347.15 nm). Travelling-wave emission occurred in the wavelength region between 485 and 650 nm. Repeat unit based absorption cross-section spectra, normalized fluorescence quantum distributions, and amplified spontaneous emission spectra are presented. Ground-state absorption cross-sections at the wavelengths of peak amplified emission are extracted from effective gain length measurements. Effective stimulated emission cross-sections are derived from pump pulse energy densities necessary for optical narrowing.     

Amplified spontaneous emission and its application for population of resonant states of the Xe and Kr atoms

To extend the capabilities of the existing spectroscopic methods of investigation and diagnostics of gaseous media, we consider a macroscopic effect of an increase in the rate of spontaneous emission, which results in the transition of a considerable part of excited molecules to lower-lying optically accessible states with light pulse emission along the direction of propagation of the exciting laser radiation. As an application of the effect of amplified spontaneous emission, we propose the population with its help of optically inaccessible electronic states of atoms and molecules.     

Effect of stimulated raman scattering on the formation of the random lasing spectrum of dyes

The nature of the line structure of the random lasing spectrum of vesicular films activated by dyes (rhodamine 6G, pyrromethene 597) has been analyzed. The spectral lines appear above the random lasing threshold and are manifested only within the spectrum of the amplified spontaneous radiation of dye molecules against the continuous-pedestal background. Their intensities are proportional to the product of the intensities of the pump and continuous spectrum at the frequencies of these lines, and the frequencies are exactly reproduced from pulse to pulse. The shifts of the lines are strongly correlated with the pump frequency and the frequencies of these lines coincide with the frequencies of the Raman scattering lines of dye molecules. Using these properties, it has been shown that the observed lines are due to stimulated resonant Raman scattering by dye molecules, which occurs simultaneously with the stimulated emission of these molecules. These two processes affect each other and jointly form a united nonlinear process where all of the oscillations active in Raman scattering are manifested.     

Theoretical investigation of amplified spontaneous emission with picosecond light pulses in dye solutions

The amplified spontaneous emission in dye solutions excited with intense picosecond light pulses is studied theoretically. A multi-level model is applied to take into account the effects of the various dye parameters such as ground-state absorption, stimulated emission, excited-state absorption, reabsorption and relaxations from populated excited levels. The influence of the pump laser duration and intensity and of the dye concentration and sample length is investigated. Optimum situations are derived for the generation of intense picosecond light pulses at new frequencies by amplified spontaneous emission. On the other hand, conditions are found where amplification of spontaneous emission may be neglected. The analysis allows the determination of unknown dye parameters by comparing the calculations with the experiment.     

光诱导分布反馈激发染料掺杂向列相液晶的放大自发发射

随着OLEDs的发展,有机/聚合物材料体系的放大自发发射也得到了广泛深入的研究。利用Lloyd镜面体系构建了分布反馈体系,研究了DCJTB在向列相液晶中的放大自发发射过程,利用布拉格方程计算了发射光谱的峰值波长。实验结果表明,DCJTB向列相液晶体系的放大自发发射阈值为与平面波导结构相比,分布反馈体系提供了良好的模式,半峰全宽明显变窄;随着电场的变化,不同角度的输出信号强度也变化明显,利用电场可以有效的对TE、TM两种模式的强度进行调制。     

Effects of gordon-haus jitter on soliton transmission

The bit error rate (BER) performance of an optical soliton communication system is analyzed. Based on the jitter variance equation and the chi-square distribution for the amplified spontaneous emission noise, an analytic expression for the BER calculation is obtained. We have investigated the effects of Gordon-Haus jitter, which is due to the random phase shift of the soliton individual central wavelength induced by the amplified spontaneous emission noise of the amplifiers. Very good agreement has been obtained between our theory and the reported experimental results.     

Room-temperature amplified spontaneous emission at 1300 nm in solution-processed PbS quantum-dot films

We report room-temperature amplified spontaneous emission and spectral narrowing at infrared wavelengths in solution-processed films made up of PbS quantum-dot nanocrystals. The results are relevant to optical amplification and lasing integrated upon a variety of substrates. The active optical medium operates at room temperature without any additional matrix material, providing an optical gain of 260 cm(-1) and a pump threshold of 1 mJ/cm(-2). Nanocrystals synthesized in an aqueous solution and stabilized by use of short ligands result in high quantum-dot volume fractions in solid films and in a redshift emission relative to absorption.     

Two-photon absorption and emission dynamics of bulk GaAs

Bulk n-type GaAs (dopant silicon) is investigated with picosecond pump pulses of a passively mode-locked Nd:glass laser. The two-photon absorption, the spontaneous emission, and the longitudinal amplified spontaneous emission are measured. The experimental results are compared with computer simulations and relevant material parameters are determined.     

Glass-clad Cr4+:YAG crystal fiber for the generation of superwideband amplified spontaneous emission

Glass-clad Cr4+:YAG crystal fiber is demonstrated by a codrawing laser-heated pedestal growth method. As much as 2.45 mW of superwideband amplified spontaneous emission (ASE) is generated in the optical fiber communication band with a 3-dB width of 240 nm. The simulation indicates that the ASE power could be in excess of 20 dBm for a 5-microm-diameter core at a pump power of 2.5 W.     

Investigation on RF styrene plasma by emission spectroscopy

In order to gain an insight into the processes in an RF styrene plasma, gas phase plasmas were investigated by emission spectroscopy. The plasma reactor was a bell-jar-type chamber with two parallel plate electrodes. The measurement of plasma emission spectra was made with axial resolution. The correlations among the emission intensities of CH and C₄H₂⁺ species, the polymer deposition rate and the polymeric structure of the deposited films were studied. The proposed analysis showed that the gas flow pattern in the plasma reactor, and the difference in collisions between styrene monomer molecules and energetic free electrons occurring in the plasma region and RF sheath, made the fragments and ions produced change in the different regions, resulting in a change in polymeric structure and deposition rate of the polymer films. With increasing distance between the substrate position and the lower electrode, the deposition rate and the concentration of phenyl groups both at the polymer surface and in the bulk decreased     

Spatially inhomogeneous saturation of gain in organic solutions caused by amplified spontaneous emission

A theoretically predicted phenomenon, the spatially inhomogeneous saturation of the gain caused by amplified spontaneous emission, was investigated. The direct measurements of the population of excited states are in good qualitative agreement with the theoretical calculations.     

原电池法室温制备Ba_(1-x)Ca_xMoO_4固溶体薄膜

在含Ca_~(2+)和Ba~(2+)的碱性溶液中,通过原电池法在室温条件下制备了Ba_(1-x)Ca_xMoO_4多晶固溶体薄膜。通过X射线衍射(XRD)、扫描电子显微镜(SEM)、X射线光电子能谱(XPS)和荧光分析(FA)对所制备的薄膜进行了分析表征,研究了Ba摩尔分数对薄膜的晶相结构、表面形貌和发光性能的影响。结果表明,原电池法制备的Ba_(1-x)Ca_xMoO_4薄膜致密、均匀、结晶完好,为四方相结构。随着初始溶液中Ba含量的增加,所得Ba_(1-x)Ca_xMoO_4固溶体薄膜的形貌逐渐从CaMoO_4微晶的球形转变为BaMoO_4微晶的四方锥形。在290nm紫外光的激发下,制备的薄膜均在350nm和495nm附近呈现两个宽的发射带,其中495nm的蓝光发射明显强于350nm的紫光发射。初始溶液中的Ba/Ca的量比对所制备的Ba_(1-x)Ca_xMoO_4固溶体薄膜的发射光谱的形状和发射波长影响甚微,但对其发射强度有明显影响。     

Emission spectrum of concentrated dye solutions excited by high-power laser radiation

Emission spectra of concentrated (~10¹⁸–10¹⁹ cm^–3) ethanol solutions of Rhodamine C excited by high-power (~10²⁵–10²⁶ cm^–2s^–1) laser radiation were measured. The emission spectrum consists of two narrow bands (with half-widths of ~200–300 cm^–1). The long-wavelength band was interpreted as cooperative spontaneous emission, and the short-wavelength band was assigned to the amplified spontaneous emission. The ratio of their intensities depends on the dye concentration and the pump power density. The ratio of band intensities is assumed to be determined by the dephasing rate of excited molecules responsible for cooperative spontaneous emission.     

Population inversion in fluorescing fragments of super-excited molecules inside an air filament

An original idea is reviewed.When a molecule is pumped into a super-excited state,one of its decay channels is neutral dissociation.One or more of the neutral fragments will fluoresce.Hence,if a lower state of such fluorescing fragments was populated through other channels but with a lower probability,population inversion of the fluorescing fragments would be naturally realized.This idea seems to be validated,so far,by comparing published work on three hydrocarbon molecules,CH4,C2H2,C2H4,and water vapor,H2O.After super-excitation in a femtosecond laser filament in air mixed with these molecules,the fluorescence from the CH or OH fragments exhibits population inversion,i.e.,amplified spontaneous emission was observed in the backscattering direction of the filament.     

Effects of gordon-haus jitter on soliton transmission

Abstract

The bit error rate (BER) performance of an optical soliton communication system is analyzed. Based on the jitter variance equation and the chi-square distribution for the amplified spontaneous emission noise, an analytic expression for the BER calculation is obtained. We have investigated the effects of Gordon-Haus jitter, which is due to the random phase shift of the soliton individual central wavelength induced by the amplified spontaneous emission noise of the amplifiers. Very good agreement has been obtained between our theory and the reported experimental results.     

Spontaneous-emission spectrum of the nonlasing supermodes in semiconductor laser arrays

It is shown that the interference between amplified spontaneous emission into the nonlasing supermode and the laser field of a semiconductor laser array causes spatial hole burning, which couples the dynamics of the amplified spontaneous emission with the laser field. In particular, phase locking between the amplified spontaneous emission and the lasing mode leads to the formation of a spectral triplet composed of in-phase relaxation oscillation sidebands and an out-of-phase line at the lasing frequency.     

交叉增益调制型波长转换器噪声特性的研究

对基于半导体光放大器的交叉增益调制型波长转换器相向和同向两种工作方式进行了研究。实验上分别实现了两种工作方式在1550nm波段的波长转换,比较了相同外部条件下两种工作方式的噪声特性,在全面考虑放大自发辐射噪声及其消耗载流子,增益谱的色散性和有源区内部损耗等因素的基础上,运用放大器的分段模型,计算了不同条件下两种方式的输出噪声功率,结果表明：相向型工作方式受放大自发辐射噪声的影响要远大于同向工作方式,输出放大自发辐射噪声功率的大小主要取决于载流子浓度的高低,而载流子空间分布的不均匀程度则决定两种工作方式输出噪声功率的差值大小。     

Laser performance and photostability of Rhodamin B in solid host matrices

Laser dye Rhodamine B was incorporated at different concentrations in GMA polymer, sol–gel glass and organic–inorganic hybrid material synthesized using the sol–gel process. The amplified spontaneous emission (ASE) was studied using Nd-YAG laser of 532 nm. The effect of laser excitation in transfer pumping configuration and the influence of dye concentration on the ASE were studied. Also, the gain and the energy conversion efficiencies were investigated. Relatively high efficiencies (to ～48%) were obtained with good photostabilities where a decrease to ～30% of the initial amplified spontaneous emission output energy were observed after pumping by 35000 shots at relatively high repetition rate (10 Hz) and energy (15 mJ). The composition and the properties of the matrix were found that optimize the laser performance and photostability of an investigated dye.