Soft X-Ray Laser Gain from Neon like Gallium and Germanium

Gain coefficients are calculated for neon-like gallium and germanium ions. Shorter wavelengths are calculated and predicted to be emitted. The gain coefficients are calculated among 457 energy levels of the neon-like ions. Collisional excitations were calculated through the distorted wave approximations through five electron temperatures Te = 300, 500, 700, 1000 and 1500 eV.

Strongly Gain Coupled DFB Laser Monolithically Integrated with a Self Alignment Spot Size Converter

A new type strongly gain coupled (GC) DFB laser and a new type self alignment spot size converter (SA SSC) are proposed and successfully fabricated.The strongly GC DFB laser is monolithically integrated with the SA SSC with three step epitaxies.A high single mode yield and large side mode suppression ratio is obtained from the strongly GC DFB laser.A near circle far field pattern is obtained by using the SA SSC.

A theoretical and experimental investigation of an in-band pumped gain-switched thulium-doped fiber laser

In this paper, the theoretical rate equation model of an in-band pumped gain-switched thulium-doped fiber （TDF） laser is investigated. The analytical formulations of pump energy threshold, peak power extraction efficiency, and pulse extraction efficiency are derived through analyzing the interaction process between the pump pulse and the laser pulse. They are useful for understanding, designing, and optimizing the in-band pumped TDF lasers in a 1.9 μm-2.1 μm wavelength region. The experiment with an all-fiber gain-switched TDF laser pumped by a 1.558-μm pulse amplifier is conducted, and our experimental results show good agreement with theoretical analysis.

Passively Mode-Locked Femtosecond Disordered Crystal Laser with Nd:CGA as Gain Medium

We present a laser-diode-pumped passively mode-locked femtosecond disordered crystal laser by using Nd：CaGdAI04 （Nd：CGA） as the gain medium. With a pair of SF6 prisms to control the dispersion compensation, laser pulses as short as 850fs at 1079nm are obtained with a repetition rate of 124.6 MHz. The measured threshold pump power is 1.45 W. A maximum average output power of 122mW is obtained under the pump power of 5.9 W. These results show that Nd：CGA could be a promising laser medium for generating femtosecond ultrashort pulse at about 1 μm.

A kW Continuous-Wave Ytterbium-Doped All-Fiber Laser Oscillator with Domestic Fiber Components and Gain Fiber

We demonstrate a kW continuous-wave ytterbium-doped all-fiber laser oscillator with M1 domestic fiber compo- nents： a 7× I fused fiber bundle combiner, a fiber Bragg grating and a double-clad gain fiber. The oscillator operates at 1079.48nrn with 80.94% slope efficiency and shows no limit of temperature and nonlinear effects. These indicate that the passive fiber components and the gain fiber are all qualified for the high power environ- ment. No evidence of the signal power roll-over shows that this oscillator possesses the capacity to higher output with available pump power.

EXPERIMENTAL STUDIES ON SOFT X-RAY LASER GAIN

Soft X-ray laser gain experiments were successfully carried out to test recombination pumping scheme at the 6-beam laser facility and the LF12 laser facility of Shanghai Institute of Optics and Fine Mechanics, Academia Sinica. Amplifications of soft X-ray spontaneous emission (ASE) have been observed in Li-likealuminium and silicon ions in plasmas produced by irradiation of slab targets with line-focused lasers. Time-integrated intensities of the Li-like aluminum and silicon ion spectral lines emitted along the axis of the plasma show that the intensities of the spectral lines for Al^(10+) 5f—3d (105.7) and Si^(11+)+5f—3d (88.9) and 5d—3p (87.3) transitions increase nonlinearly with plasma lengths, and the corresponding gain coefficients are 3.1±0.9, 1.5±0.5, and 1.4±0.5cm^(-1), respectively, the maximum gain-length product being about 2.5. These results were obtained at much lower intensity of driving laser, 1.5—2.0×10^(12)W/cm^2.

Analysis of gain distribution in cladding-pumped thulium-doped fiber laser and optical feedback inhibition problem in fiber-bulk laser system

The steady-state gain distribution in cladding pumped thulium-doped fiber laser（TDFL） is analytically and numerically solved based on the rate equations including loss coefficients and cross relaxation effect. With the gain curve, a problem, which is named optical feedback inhibition（OFI） and always occurs in tandem TDFL-Ho：YAG laser system, is analyzed quantitatively. The actual characteristics of output spectra and power basically prove the conclusion of theoretical analysis. Then a simple mirror-deflected L-shaped cavity is employed to restrain the external feedback and simplify the structure of fiber-bulk Ho：YAG laser. Finally, 25 W of 2097-nm laser power and 51.2% of optical-to-optical conversion efficiency are obtained, and the beam quality factor is less than 1.43 obtained by knife-edge method.

Control of gain and thermal carrier loss profiles for mode optimization in 980-nm broad-area vertical-cavity surface-emitting lasers

Optical gain and thermal carrier loss distributions regarding current diffusion and various electric contact areas are investigated to improve the near-field modes from the ring-shape to a Gaussian-like configuration for extra-broad-area and oxide-confined vertical-cavity surface-emitting lasers. In this work an equivalent circuit network model is used. The resistance of the continuously-graded distributed Bragg reflectors （DBRs）, the current diffusion and the temperature effect due to different electric-contact areas are calculated and analyzed at first, as these parameters affect one another and are the key factors in determining the gain and thermal carrier loss. Finally, the gain and thermal carrier loss distributions are calculated and discussed.

Fabrication of 1.3μm InGaAsP/InP Gain-Coupled DFB Lasers with Loss Grating Using LPE Technique

In this paper,the fabrication of 1.3μm InGaAsP/InP gain-coupled DFB lasers with lossgrating is reported for the first time.A technique of regrowth on corrugated surface usingLPE is developed.By using GaAs as the cover of thermal protection and controlling theamount of the super cooling,high quality epitxial layers on corrugated surface are obtained.The oxide stripe lasers with a stripe width of 20μm are fabricated.Single-mode oscillation isachieved at 1.293μm,and a high single-mode oscillation yield is also obtained.

Pressure Dependence of the Small-Signal Gain and Saturation Intensity of a Copper Bromide Laser

A pair of copper bromide lasers in an oscillator–amplifier configuration is used to investigate the small signal gain and saturation intensity as amplifying parameters and output power of lasers, versus pressure of buffer gas. It is shown that the amplifying parameters and laser output power have a maximum value at optimum buffer gas pressure of 11？Torr. The challenge between microscopic parameters such as stimulated emission cross section, laser upper level lifetime, and population inversion, which determine the values of laser characteristics respective to the operational pressure of buffer gas, are investigated. Thus an optimum delay time of about 10？ns is determined, and a maximum output power equivalent to about 12？W is extracted. The amplifying parameters and measured output power of laser versus delay times show some local maxima and minima at the delay time interval of 6–43？ns.

Theoretical study on interaction of neon like Ge X－ray lasers in gain saturation

ＴｈｅｏｒｅｔｉｃａｌｓｔｕｄｙｏｎｉｎｔｅｒａｃｔｉｏｎｏｆｎｅｏｎｌｉｋｅＧｅＸ－ｒａｙｌａｓｅｒｓｉｎｇａｉｎｓａｔｕｒａｔｉｏｎＷａｎｇＧｕａｎｇ－Ｙｕ（王光裕）（ＩｎｓｔｉｔｕｔｅｏｆＡｐｐｌｉｅｄＰｈｙｓｉｃｓａｎｄＣｏｍｐｕｔａｔｉｏｎ...

Laser-PSD视觉焊缝自动跟踪系统的研究

设计了一种扫描式 Laser-PSD视觉焊缝自动跟踪系统 ,该系统采用激光二极管作为信号光源、1维位敏元件 (PSD)为接收器件组成视觉传感器 ,并采用单片机作为中央控制器。传感器在坡口上方横向扫描 ,获得坡口的 2维图形 ,经单片机系统处理计算得出高低、左右偏差 ,控制焊炬的高低、左右位置 ,实现了对大坡口埋弧自动焊全过程的有效跟踪。通过使用 ,证明该系统跟踪精度高 ,抗干扰能力强 ,工作可靠 ,能直观显示坡口图像和跟踪状况 ,操作方便 。

用于1.44μm半导体激光器的GaInAs/InGaAsP量子阱结构的设计

采用有效质量模型下的 4× 4Luttinger Kohn哈密顿量矩阵对GaxIn1 -xAs/In0 .80 Ga0 .2 0 As0 .4 4P0 .56 /InP量子阱结构进行了能带计算 ,求得了该量子阱结构跃迁能量随组份及阱宽的变化关系 ,从而得到了激射波长 1.44 μm时的Ga组份x与阱宽Lw(在 5～ 10nm内取值 )的相互关系 :x=0 .3 2 0 13 +0 .0 60 93Lw-0 .0 0 5 3 4Lw2 +0 .0 0 0 17483Lw3,当阱宽为 5～ 10nm ,因而Ga组份为 0 .5 1～ 0 .5 7时 ,阱材料中产生的张应变量为 :0 .2 9%～ 0 .70 %。最后 ,我们计算了该量子阱结构的能量色散关系和光增益谱 ,从而对x与Lw 组合值进行优化。

Random Laser of R6G Dye and TiO₂Nanoparticals Doped in PMMA Polymer

The random laser (RL) based on organic Rhodamine 6G (R6G) laser- dye and Titanium dioxide (TiO2) suspended nanoparticles have been prepared with polymethylmethacrylate (PMMA) as a host. Both liquid and spray-coated homogeneous film samples of 22.4 μm - 30.1 μm thickness range were use. Optimum concentrations have been determined depending on the normal fluorescence spectra which give evidence that the laser dye provides amplification and TiO2 nanoparticles as scatter center. At the optimum concentrations, results of the random laser (RL) under second harmonic Nd: YAG laser ex-citation show that the values of bandwidth at full width half-maximum (FWHM) and the threshold energy are about 9 nm and 15 mJ respectively, which represent the minimum value for the liquid samples in the current research. Correspondly, these values become 14 nm and 15 mJ for film sample. The broadening that can be attributed to the concentration quenching of a laser dye at high concentration levels has been observed.

Theoretical study of Ni-like Ag 13.9 nm TCE x-ray laser driven by two picosecond pulses

The Ni-like Ag 13.9 nm x-ray laser has been previously demonstrated that the higher gain near critical surface contributes little to the amplification of the x-ray laser because of severe refraction. In this paper, the transient collision excitation （TCE） Ni-like Ag 13.9 nm x-ray laser is simulated, driven by two 3 ps short pulse preceded by a 330 ps long prepulse, optimization of the peak to peak delay time of the two short pulses is made to get the best results. Simulation indicates that by producing lowly ionized preplasma with smoothly varying electron density, it is possible to decrease electron density gradient in higher density region, and thus higher gains near this region could be utilized, and if the main short pulse is delayed by 900ps, local gains where electron density larger than - 4 × 10^20 cm^-3 could be utilized.

Stochastic Resonance in Quantum-Well Semiconductor Lasers

The quantum well （QW） semiconductor lasers have become main optical sources for optical fibre communication systems because of their higher modulation speed, broader modulation bandwidth and better temperature characteristics. In order to improve the quality of direct-modulation by means of the stochastic resonance （SR） mechanism in QW semiconductor lasers, we investigate the behaviour of the SR in dlrect-modulated QW semiconductor laser systems. Considering the cross-correlated carrier noise and photon noise, we calculate the power spectrum of the photon density and the signal-to-noise ratio （SNR） of the direct-modulated laser system by using the linear approximation method. The results indicate that the SR always appears in the dependence of the SNR on the bias current density, and is strongly affected by the cross-correlation coefficient of the carrier and photon noises, the frequency of modulation signal, and the photon lifetime in the laser cavity.

Exact Solution to Rate Equation with Time-Dependent Coefficients： Its Application in InGaAsP Lasers

By using the algebraic dynamics method, we obtain exact analytical solutions of rate equations with time-dependent coefficients, which might present an effective description of the physical mechanism of the practical semiconductor lasers. Based on the exact solutions, we investigate the dynamic behaviour and the emitted properties of the InGaAsP laser, which has been commonly used in long wavelength optical communication systems. It is found that when the cavity length varies with time exponentially, the output power of the laser will drop and approach its asymptote. When the cavity length is a sinusoid function of time, the intensity of the emitted optical pulses can be controlled by the amplitude of this function.

The λ-Characteristics of the Ring Laser Based on Non-Uniform SOA

Semiconductor optical amplifier-based ring cavity laser (SOA-RL), which has been widely used in optical communications, optical fiber sensing, and biophotonics fields, can be tuned at an ultra high speed up to Mega Hertz over 100 nm bandwidth range with high SNR and flatness output. A steady-state model and segmentation algorithms are employed to investigate the gain spectra of four kinds of non-uniform SOA and the lasing wavelength of the SOA-RL. It shows that the dependence of the lasing wavelength on the average width is stronger when the light propagates from narrower to wider end than conversely, and there are some particular structures to show ultra high stability lasing wavelength. It is supposed that the main reason could be the carrier density distribution along the propagation.

Numerical study on the performance of nozzle flow for supersonic chemical oxygen-iodine lasers

Laser performance is greatly dependent on its operating conditions due to the strong coupling among multi- physics such as gas-dynamics, chemical reaction kinetics and optics in the mixing nozzle of COIL. In this paper, 3D CFD technology is used to simulate the mixing and reactive flow of subsonic cross jet scheme at different conditions. Results obtained show that the jet penetration depth plays a dominant role in the spatial distribution of small signal gains. In the case of over-penetration, unsteady flow structures are induced by impinging between the opposing jets. The optimum spatial distribution of the chemical performance cannot be obtained even if the full penetration condition is achieved through the subsonic transverse jet mixing scheme in the COIL nozzle flow.

Search for Laser Lines in Sodium like Fe Plasmas

Energy levels, transition probabilities and effective collision strength for 1s2 2s2 2p6 3l, 4l, 5l (l = 0, 1, 2, 3, 4) states of sodium like Fe are used in the determination of the reduced populations for 21 fine structure levels over a wide rang of electron density values (1018 to 1020 cm–3) and at against electron plasma temperatures. Gain coefficients are evaluated and plotted against the electron density.