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.

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.

Laser-annealing-made amplified spontaneous emission of "giant" CdSe/CdS core/shell nanocrystals transferred from bulk-like shell to quantum-confined core

'Giant' Cd Se/Cd S core/shell nanocrystals(NCs) were synthesized with thick Cd S shell(15 monolayers), and the x-ray diffraction(XRD) measurement indicates there is a zinc blende phase in the thick Cd S shell, whereas it transformed into wurtzite phase under 5 min radiation with a 400 nm, 594 μJ∕cm2femtosecond(fs) laser beam.The evolution of the NCs’ spontaneous emission under the fs laser radiation was recorded with a Hamamatsu streak camera. The as-synthesized NCs exhibit an amplified spontaneous emission(ASE) at 530 nm, which comes from a bulk-like Cd S shell due to the interfacial potential barrier, which could slow down the relaxation of holes from the shell to the core. After being annealed by an fs laser, the ASE of the g-NCs is transferred from a bulk-like Cd S shell to a quantum-confined Cd Se core because the phase transformation determined with the XRD measurement could remove the interfacial barrier. Besides the ASE at 643 nm, two shorter-wavelength ASE peaks at 589 and 541 nm, corresponding to optical transitions of the second(1P) and third(1D) electron quantization shells of the Cd Se core, also appear, thus indicating that Auger recombination is effectively suppressed.

Pump pulse characteristics of quasi-continuous-wave diode-side-pumped Nd:YAG laser

The influence of pumping laser pulse on the property of quasi-continuous-wave(QCW)diode-side-pumped Nd:YAG laser is investigated theoretically and experimentally.Under remaining a fixed duty cycle,the average output power increases,and the corresponding thermal focal length shorten with the increase of the pump pulse duration,which attributes to the decrease of the ratio of pulse buildup time to the pulse duration.At a pump power of 146 W,the laser output power changes from 65.1 W to 81.2 W when the pulse duration is adjusted from 150μs to 1000μs,confirming a significant enhancement of 24.7%.A laser rate equation model incorporating the amplified spontaneous emission is also utilized and numerically solved,and the simulated results agree well with the experimental data.

相位分布管理的准二维钙钛矿薄膜在纳秒脉冲激光泵浦下实现高效放大自发发射

准二维钙钛矿表现出独特的光物理性质,这使它们成为激光技术潜在进步的优秀候选材料.高性能纳秒脉冲激光和放大自发发射(ASE)是实现连续波抽运光电泵浦激光器的关键工艺.然而,在纳秒脉冲激光泵浦下发展准二维钙钛矿ASE或激光仍然存在一些困难,包括表面缺陷浓度高、俄歇复合和能量传递效率低.本文通过无添加剂的Cs^(+)阳离子掺杂策略,可以很好地控制准二维钙钛矿膜的形貌和相分布,从而解决了低n相导致的能量传递途径不足的问题.本文通过快速的能量传递过程揭示了增益性质和载流子复合.基于此,掺杂适当比例Cs^(+)阳离子的PEA_(2)(FA_(0.7)Cs_(0.3))_(2)Pb_(3)Br_(10)钙钛矿膜的净增益系数比原始钙钛矿薄膜提高了近3倍,从而将纳秒激光激发下的放大自发发射阈值降低到1/3.研究结果表明,在准二维钙钛矿中掺杂Cs^(+)可为实现高性能激光器件的相位分布设计提供见解.

Controllable optical emission wavelength in all-inorganic halide perovskite alloy microplates grown by two-step chemical vapor deposition

All-inorganic halide perovskites(IHP),CsPbX_(3)(X=Cl,Br,I)exhibiting efficient optical emissions within the spectral range of 410 to 730 nm are potential candidates for many optoelectronic devices.Anion alloying of these IHPs is expected to achieve tunable emission wavelength covering the entire visible spectrum.Here,we developed a two-step chemical vapor deposition(CVD)process for growing quaternary IHP CsPbX_(3)(X=Cl/Br and Br/I)alloys.By exploiting the fast diffusion of halide anions in IHPs,the alloy composition can be precisely controlled by the growth time of the respective layers once the growth of the individual ternary IHP is optimized.Hence complexities in the multi-parameter optimization in the conventional CVD growth of quaternary alloys can be mitigated.Using this process,we synthesized single crystalline,homogeneous and thermally stable CsPbCl3_((1−X))Br_(3x)and CsPbBr3_((1−X))I_(3x)perovskites alloy microplates and demonstrated continuously tunable emission covering the spectrum from 428 to 715 nm by varying the halide compositions in the alloys.These alloy microplates also exhibit room temperature amplified spontaneous emissions(ASE)along with strong photonic discharges from the microplate’s edges and hence are potentially useful as a gain medium as well as optical cavities for emissions with wavelengths covering the visible spectrum.

Theoretical Modelling of Cascaded Er3+-Doped, Tm3+-Doped and Nd3+-Doped Fibers for 0.4 to 2.0 μm Emission Spectra

We present a cascaded system designed with Er^3+-Doped,Tm^3+-doped and Nd^3+-doped fibers to realize amplified spontaneous emission(ASE)spectra covering 0.4—2.0μm.The system is excited with a pump laser emitting 808 nm photons with 500 m W pump power.The emission spectra of the cascaded system covering0.4—2.0μm are realized with the Er^3+,Tm^3+and Nd^3+ion doping densities optimized to 8×10^19,2×10^20 and8×10^20 ion/m^3,respectively,and the fiber length optimized to 1 m.Numerical methods reveal that the peak ASE power for the cascaded system can reach 20.9 m W.A minimum ASE power of 4.39 m W is attainable.Using numerical calculations and analytical techniques,we provide a detailed insight into optimized Er^3+-doped,Tm^3+-doped and Nd^3+-doped fiber lengths and their doping concentrations for ASE power spectra covering 0.4—2.0μm.We believe that the cascaded system can potentially provide significant applications in various optical fields which include but not limited to wavelength-division multiplexing,various optical communications and other salient medical imaging processes.

Improving the performance of high-power broad-area lasers by suppressing cavity modes propagating in the lateral dimension

We first study the effect of cavity modes propagating in the lateral dimension on high-power semiconductor lasers with a large stripe width.A sidewall microstructure was fabricated to prevent optical feedback of lateral resonant modes.Theoretically,we demonstrate the existence of lateral resonant modes in the Fabry–Perot cavity with a large stripe width.Experimentally,we design the corresponding devices and compare them with conventional broad-area diode lasers.About a 15%reduction in threshold current and a 27%increase in maximum electro-optical conversion efficiency are achieved.The amplified spontaneous emission spectrum is narrowed,which proves that lateral microstructures suppress optical feedback of lateral resonant modes.Under a large continuous-wave operation,the maximum output power of laser device is43.03 W,about 1 W higher than that of the standard broad-area laser at 48 A.

External focusing dependence of spatial distribution of air lasers during femtosecond laser filamentation in air

The spatial distribution of the forward-propagating amplified spontaneous emission(ASE) of nitrogen molecular ions during femtosecond laser filamentation in air is studied via numerical simulations. The results suggest that the divergence angle and signal intensity are extremely sensitive to the external focal length. Concurrently, we show that the optical Kerr effect plays a significant role in concentrating the directivity of ASE signals, particularly in cases of loose focusing. Furthermore,the simulations demonstrate that ASE signals are enhanced for a tight focus, although the corresponding filament length is shorter. The main physical mechanism underlying this process is the competition between the plasma defocusing and optical Kerr effects. The result is important for filamentation-based light detection and ranging applied to remote sensing.

Intense,wideband optical waveform generation by self-balanced amplification of fiber electro-optical sideband modulation

We demonstrate a simple method to obtain accurate optical waveforms with a gigahertz-level programmable modulation bandwidth and a watt-level output power for wideband optical control of free atoms and molecules.Arbitrary amplitude and phase modulations are transferred from microwave to light with a low-power fiber electro-optical modulator.The sub-milliwatt optical sideband is co-amplified with the optical carrier in a power-balanced fashion through a tapered semiconductor amplifier(TSA).By automatically keeping TSA near saturation in a quasi-continuous manner,typical noise channels associated with pulsed high-gain amplifications are efficiently suppressed.As an example application,we demonstrate interleaved cooling and trapping of two rubidium isotopes with coherent nanosecond pulses.

Ultrahigh temporal contrast performance of the PHELIX petawatt facility

We report on the temporal contrast performance of the PHELIX facility in view of the requirements imposed by solidtarget interaction experiments. The requirement analysis for the nanosecond and picosecond temporal contrast is derived from empirical data and simple theoretical modeling, while the realization shows that using an ultrafast optical parametric amplifier and plasma mirrors enables meeting this specification.