Nonlinear Absorption and Low-threshold Two-photon Pumped Amplified Stimulated Emission from FAPbBr_(3) Nanocrystals

Formamidinium lead bromide(FAPbBr_(3))nanocrystals(NCs)have been considered to be a good optoelectronic material due to their pure green emission,excellent stability and superior carrier transport characteristics.However,two-photon pumped amplified spontaneous emission(ASE)and the corresponding nonlinear optical properties of FAPbBr_(3) NCs are scarcely revealed.Herein,we synthesized colloidal FAPbBr_(3) NCs with different sizes by changing the molar ratio of FABr/PbBr_(2) in the precursor solution,using ligand assisted precipitation(LARP)technology at room temperature.Photoluminescence(PL)and time resolved photoluminescence(TRPL)spectroscopy were measured to characterize their ASE properties.And their nonlinear optical properties were studied through the Zscan technique and the two-photon excited fluorescence method.The stimulated emission properties including oneand two-photon pumped ASE have been realized from FAPbBr_(3) NCs.With large two-photon absorption coefficient(0.27 cm/GW)and high non-linear absorption cross-section(7.52×10^(5) GM),ASE with threshold as low as 9.8μJ/cm^(2) and 487μJ/cm^(2) have been obtained from colloidal FAPbBr_(3) NCs using one-and two-photon excitations.These results indicate that as a new possible green-emitting frequency-upconversion material with low thresholds,FAPbBr_(3) NCs hold great potential in the development of high-performance two-photon pump lasers.

Impact of amplified spontaneous emission noise on the SRS threshold of high-power fiber amplifiers

Impact of amplified spontaneous emission(ASE)noise on the stimulated Raman scattering(SRS)threshold of highpower fiber amplifiers is demonstrated numerically through a spectral evolution approach.The simulation results confirm that ASE noise in the Raman wavelength band could reduce the SRS threshold of high-power fiber amplifiers significantly.As for ASE noise originated the main amplifier,it becomes stronger and reduces the SRS threshold at shorter operation wavelength below 1052 nm.As for ASE noise originated from the seed laser,it reduces the SRS threshold at different operation wavelength under the condition that the Raman ratio is over-90 dB in the seed laser.The theoretical method and results in this work could provide a well reference to extend the operation wavelength of high-power fiber lasers.

A Temperature-Insensitive Amplified Spontaneous Emission Broadband Source Based on Er-Doped Fiber

To obtain a stable amplified spontaneous emission（ASE） source for complex environment applications, we design an ASE source and study the output power and spectral characteristics under different ambient temperatures.We optimize the structure of the ASE source to flatten the ASE spectrum, and study the output characteristics in terms of output power and optical spectrum under different pump powers. Then the performance of the ASE source is investigated in the temperature range from-18.9°C to 50°C. A stable-power and flat-spectrum ASE source can be obtained by structural optimization and pump control.

Solvent-vapour treatment induced performance enhancement of amplified spontaneous emission based on poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene]

In this work, performance enhancements of amplified spontaneous emission （ASE） from poly[2-methoxy-5-（2＇- ethyl-hexyloxy）-l,4-phenylene vinylene] （MEH-PPV） have been achieved via solvent vapour treatment. Correlations between the morphology of the film and the optical performance of polymer-based ASE are investigated. The active layers are characterised by atomic force microscopy and optical absorption. The results show that the solvent-vapour treatment can induce the MEH-PPV self-organisation into an ordered structure with a smooth surface, leading to enhanced optical gain. Thus the solvent-vapour treatment is a good method for improving the optical properties of the MEH-PPV.

Broadband amplified spontaneous emission from Er^3＋ -doped single-mode tellurite fibre

This paper reports on the fabrication and characterization of a newly erbium-doped single-mode tellurite glass-fibre applicable for 1.5-μm optical amplifiers. A very broad erbium amplified spontaneous emission in the range 1450-1650 nm from erbium-doped single-mode tellurite glass-fibre is obtained upon excitation of a 980-nm laser diode. The effects of the length of glass-fibre and the pumping power of laser diode on the amplified spontaneous emission are discussed. The result indicates that the tellurite glass-fibre is a promising candidate for designing fibre-optic amplifiers and lasers.

Theoretical study of amplified spontaneous emission intensity and bandwidth reduction in polymer

Amplified spontaneous emission （ASE）, including intensity and bandwidth, in a typical example of BuEH-PPV is calculated. For this purpose, the intensity rate equation is used to explain the reported experimental measurements of a BuEH-PPV sample pumped at different pump intensities from Ip = 0.61 MW/cm2 to 5.2 MW/cm2. Both homogeneously and inhomogeneously broadened transition lines along with a model based on the geometrically dependent gain coefficient （GDGC） are examined and it is confirmed that for the reported measurements the homogeneously broadened line is responsible for the light-matter interaction. The calculation explains the frequency spectrum of the ASE output intensity extracted from the sample at different pump intensities, unsaturated and saturated gain coefficients, and ASE bandwidth reduction along the propagation direction. Both analytical and numerical calculations for verifying the GDGC model are presented in this paper. Although the introduced model has shown its potential for explaining the ASE behavior in a specific sample it can be universally used for the ASE study in different active media.

Effect of different metal-backed waveguides on amplified spontaneous emission

We investigate the effect of a metallic electrode on the ability for poly[2-methoxy-5-（2＇-ethylhexyloxy）-1,4- phenylene vinylene] （MEH-PPV） film to undergo amplified spontaneous emission （ASE）. The threshold of the device with Ag cladding is about 10 times greater than that of a metal-free device, but metal such as Al completely shuts off ASE. The ASE recurs when a thin spacer layer, such as a few nanometers of SiO2, is introduced between the MEH-PPV film and the Al cladding. Compared with the Cu or Al electrode, the Ag cladding is most suited to serve as an electrode with its low optical loss due to its high work-function and reflectivity.

Amplified spontaneous emission from metal-backed poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene] film

We investigate the amplified spontaneous emission （ASE） from an Ag-backed poly[2-methoxy-5-（2＇-ethylhexyloxy）- 1,4-phenylenevinylene] （MEH-PPV） film with different film thicknesses. The ASE characteristics of Ag-backed MEH- PPV films with different thicknesses show that increasing the film thickness can reduce the influence of the Ag cladding. The threshold, the gain, and the loss of the device with a thickness of 170 nm are comparable to those of a metal-free device. The lasing threshold of this device is about 7.5 times that of a metal-free device. Our findings demonstrate that Ag-backed MEH-PPV film with an appropriate thickness can still be a good polymer gain material for the fabrication of solid-state lasers.

Size-dependent Amplified Spontaneous Emission from Organic Crystal Slabs

The authors investigated size-dependent amplified spontaneous emission（ASE） from organic crystals. Specifically, N-（4-{4-[4-（diphenylamino）styryl]styryl}phenyl）-N-phenylbenzene amine（Ph-TPA2） organic crystals were used in the experiment. The ASE threshold was decreased with the decrease of the width of the crystal at the same gain length, which reflects that total internal reflection plays an important role on the ASE properties in these slab organic crystals. The ASE properties pumped by one- and two-photon were also comparatively studied. We found that the thresholds of ASE in two-photon pumping condition are less size-dependent than those in singlephoton condition because of the nonlinear light generation processes in two-photon absorption processes.

Loss prediction of three-level amplified spontaneous emission sources in radiation environment

A model of three-level amplified spontaneous emission(ASE)sources,considering radiation effect,is proposed to predict radiation induced loss of output power in radiation environment.Radiation absorption parameters of ASE sources model are obtained by the fitting of color centers generation and recovery process of gain loss data at lower dose rate.Gain loss data at higher dose is applied for self-validating.This model takes both the influence of erbium ions absorption and photon bleaching effect into consideration,which makes the prediction of different dose and dose rate more accurate and flexible.The fitness value between ASE model and gain loss data is 99.98%,which also satisfies the extrapolation at the low dose rate.The method and model may serve as a valuable tool to predict ASE performance in harsh environment.

A位取代和缺陷钝化实现钙钛矿薄膜的低阈值红光放大自发辐射

作为发红光的光学增益介质,CsPbI_(2)Br钙钛矿材料具有良好的热稳定性和合适的光学带隙,引起了研究者的广泛关注。然而,溶液法制备的CsPbI2Br薄膜在高湿度环境下易发生相变,同时薄膜存在大量缺陷,阻碍了其性能提升。鉴于此,采用部分FA^(+)(CH_(4)N_(2)^(+))进行A位取代以提高钙钛矿薄膜的相稳定性,然后利用聚甲基丙烯酸甲酯(PMMA)对钙钛矿薄膜进行表面钝化。得益于FA^(+)阳离子带来的薄膜形貌的改善和PMMA良好缺陷钝化效果,实现了Cs_(0.7)FA_(0.3)PbI_(2)Br钙钛矿薄膜的低阈值红光放大自发辐射(ASE),其发射波长为689 nm,纳秒激光激发下的阈值为15μJ/cm^(2)。同时,该薄膜具有良好的疏水性和光稳定性,在大气湿度环境下(RH为(40±10)%),采用3000μJ/cm^(2)脉冲激光持续照射120 min,其ASE强度仍能维持其初始值的93%。这项工作为实现低阈值高稳定的红光ASE和激光提供了参考。

应用于三轴光纤陀螺中的双程后向ASE光源

根据三轴光纤陀螺的高精度需求,采用大功率高稳定性的高精度双程后向方案掺铒光纤光源。通过对ASE光源的理论分析建立数学模型,并根据所用掺铒光纤及泵浦光源的参数对光源进行谱型分析,确定光路方案。再以掺铒光纤和泵浦激光器的温度特性和补偿为研究重点,对掺铒光纤的长度和掺杂浓度以及泵浦功率和铒纤的匹配性进行试验,最终采用铒纤长度19 m,泵浦波长974.6 nm,泵浦功率140 m A,得到光源光功率为20 m W,平均波长变化量小于0.5′10^(-6)/℃,满足光纤陀螺对ASE光源的要求。

掺铒光纤ASE宽带光源的实验研究

掺铒光纤ASE源是一种优良的宽带光源,受到人们广泛关注。实验研究了掺铒光纤ASE宽带光源单、双程结构后向ASE输出光谱特性,当泵浦光中心波长为1480 nm时,分别考察了掺铒光纤长度、泵浦光功率对后向ASE输出平坦区间宽度和平坦度的影响。通过对两种结构下后向ASE输出光谱的分析比较发现,双程结构在L波段长波长处,尤其是1570～1620 nm波长范围,功率显著提升,从而使得ASE光谱的平坦区间宽度增大,平坦度提高。所得实验结果将为掺铒光纤ASE宽带光源的研制提供依据。

SASE自由电子激光起振问题及统计特性的数值模拟

介绍一种自放大自发辐射自由电子激光(SASEFEL)的自发辐射和电子束噪声的数学描述,运用修正的一维非定态程序,对SASEFEL起振问题及光场统计特性进行了数值模拟,分析了自发辐射谱的发展过程及一定频带宽度内光场随机特性的统计规律,数值模拟结果与理论结果符合较好。

基于MgO:PPLN晶体的1554.8nm倍频器

为满足风云四号气象卫星搭载的闪电成像仪图像定位精度检验的光源需求,设计了一台基于两级主振荡功率放大器结构(MOPA)和掺氧化镁的周期极化铌酸锂(MgO:PPLN)晶体倍频技术,中心波长为777.4 nm,连续输出功率为1.5 W的激光器。采用反向940 nm off-peak泵浦方式较好地抑制了光放大器中自激放大辐射(ASE)和受激布里渊散射(SBS)效应,主放大器光-光转换效率达37.2%,获得了输出光功率为15 W,信噪比为59.6 dB,线宽为323.4 kHz,相对强度噪声为-145 dBc/Hz的单频窄线宽激光。在理论分析所用MgO:PPLN晶体倍频效率、温度调谐带宽以及可接收的波长带宽基础上,采用单通倍频方式获得了功率为1.5 W的777.4 nm连续光。

一种高效率的L波段掺铒光纤ASE宽带光源

利用双程双向泵浦单级掺铒光纤的结构实现高效率的L波段掺铒光纤放大自发辐射输出，同时选择1480nm半导体激光器作为泵浦源，高掺杂铒光纤为增益介质，通过优化铒光纤长度，获得了在1566～1604nm（38nm），自发辐射谱功率高于-16dBm，总输出功率13．7dBm的L波段掺铒光纤放大自发辐射光源。该光源结构相比于双程前向泵浦结构的L波段掺铒光纤放大自发辐射光源，其泵浦效率从11．8％提高到23．4％。

一种SASE-FEL用摇摆器机制探讨

利用带电粒子在均匀等离子体中传播时 ,在其后激发的尾波场作为自发辐射自放大自由电子激光(SASE -FEL)的摇摆器 ,称为尾波摇摆器。分析了此摇摆器在工作机制及其相应的周期、场强度 ,根据SASE -FEL理论计算了其增益长度Lg,并和APS的SASE实验参数作了比较。

利用C波段ASE补偿的双通掺铒光纤宽带光源(英文)

报道了一种基于掺铒光纤的两级宽带光源.通过采用双通结构和循环利用C波段放大自发辐射,极大地节省了用于产生L波段放大自发辐射所需的泵光功率.利用一支啁啾布拉格光栅作为光谱平坦器,实现了76 nm的平坦输出光谱.

高功率光纤激光器中ASE噪声的测量方法（英文）

高峰值功率脉冲光纤激光器在激光雷达系统中有着广泛的应用。然而,光纤激光器中放大自发辐射噪声(ASE)严重影响了系统的探测性能。提出一种测量高峰值功率脉冲光纤激光器中ASE噪声的方法。在该方法中,首先对高峰值功率的激光脉冲衰减,然后在时域分别测量和计算ASE噪声和激光脉冲的相对能量。给出了光纤激光器在驱动电流分别为6A,7A和8A时衰减后的ASE噪声廓线以及ASE噪声占激光脉冲能量的比例。

旋光纤喇曼放大器中ASE噪音模型及仿真计算

通过分析旋光纤喇曼放大器中信号光、抽运光的非线性薛定谔波动方程及放大自发辐射噪音特性,提出一种能同时在旋光纤喇曼放大器中产生预计波形放大自发辐射噪音,又方便计算的方法.根据放大自发辐射噪音时域特性,建立并在波动方程中加入放大自发辐射非高斯噪音模型.在考虑旋光纤双折射的非线性效应同时,通过分步傅里叶法对波动方程求解,计算了旋光纤喇曼放大器中的放大自发辐射噪音,并与实验结果吻合.