Effective suppression of beam divergence for a high-power laser diode bar by an external-cavity technique

We describe effective suppression of beam divergence for a high-power laser diode bar by use of an external-cavity technique. Nineteen off-axis external-cavity laser diodes of the high-power laser diode are formed by feedback with a stripe mirror. At three times the threshold current, the diverging angle (1/e2) of the external-cavity laser diode bar is reduced to 1.5 degrees from 6.6 degrees (free running) with 14.1-W peak output power and 70.4% of the radiated power of the free-running state without the external cavity. This technique effectively improves the beam quality of the high-power laser diode bar.     

Laser diode beam shaping by optical interference

We recently proposed a novel beam shaping technique that employs Lloyd’s mirror interference. In this study, we apply this technique to three commercial laser diodes: laser diodes used for optical pumping of solid-state lasers, for laser beam printers, and for laser displays. The elliptical output beams from these laser diodes could be transformed into nearly circular beams by inserting a mirror-polished GaAs substrate below the active layer of each laser diode and adjusting its height. The experimentally observed far-field patterns were predicted fairly well by numerical calculations based on Huygens’ integral. We confirmed that our beam shaping technique is applicable to laser diodes with various wavelengths and vertical beam divergence angles. We also describe the monolithic configuration of the beam shaping system, which can be fabricated by dry etching.     

Characteristics of Gain-Guided Laser Diodes with Cylindrical-Mirror Cavity

We have developed highly reliable etched-mirror laser diodes using a dry etching method. The lasers without facet-coating have been operating stably over 2500 h under automatic-power control (APC) at a power of 3 mW/facet at 50°C. The gain-guided laser diodes with a cylindrical-mirror cavity (CMC) have coaxial mirrors and a fan-shaped stripe structure. By decreasing the curvature radius of the inner facet or increasing the stripe width of the inner facet, the beam waist parallel to the junction plane can be moved outside of the laser diode, while the beam waist perpendicular to the junction plane stops at the mirror facet. A particular CMC laser has a low astigmatism of 4.1 μm and a low relative intensity of noise (RIN) less than –134 dB/Hz at 4 mW under 0–1% optical feedback without high frequency current superposition.     

大功率激光脉冲二极管触发高增益光导开关实验研究

研究了一种新型大功率激光脉冲二极管的输出特性,该激光二极管主要用于触发工作在高增益模式下的砷化镓光导开关。研制了基于射频金属-氧化物半导体场效应管的激光二极管驱动电路,可以为激光二极管提供上升沿、半高宽和峰值电流分别为4 ns,20 ns和130 A的脉冲驱动电流。研究了激光二极管输出的激光脉冲波形、能量、功率、光场分布等特性,并在Blumlein传输线结构中,研究了该大功率激光脉冲二极管的输出特性对工作于高增益模式下的光导开关的导通电阻、开关抖动等主要导通性能参数的影响规律。实验结果表明,激光脉冲的能量和功率越大,光斑面积越大、分布越均匀,在相同偏置电压条件下,光导开关的导通性能越好。     

外腔半导体激光器用恒流源电路设计与实现

由于外腔半导体激光器系统中的核心部分——激光器受外界环境影响较大,在装配或工作中极易受到电压、电流和静电荷的影响而损坏.为减少由于电路不稳定产生的激光器损坏,在借鉴各种传统的恒流源电路实现方式的基础上,运用反馈恒流原理,慢启动慢关闭原理,利用场效应管特性,给出一种高准确度恒流电路实现方式.将此电路直接运用于中心波长1550 nm激光器作为驱动电路,工作稳定、输出电流受负载影响很小且输出准确度达到同行业先进水平.电流稳定达到0.01％以上.此电路实现方式简单,实用性较强,对整个电路做出了实验仿真和测试,很好地解决了由于驱动电流不稳造成的激光器损坏的问题.     

基于DSP和CPLD控制的多路并行激光驱动

描述了一种基于DSP和CPLD控制的多路并行激光驱动模块的设计。这种激光驱动模块可以对多路激光管进行驱动和调制,并可兼容不同类型激光管的工作电压和工作电流。激光驱动模块已用于多波长多阶光存储实验系统,可对780nm、650nm和407nm激光器进行驱动和调制。实验结果表明,这种激光驱动模块能够实现对半导体激光器的长时间稳定驱动,并具有灵敏的高频调制能力。它对在光存储中实现波长复用存储技术具有重要作用。     

Band crossing in Pb1−xSnxSe under hydrostatic pressure

Laser emission from Pb_1−xSn_x Se diodes for x = 0.115 at 78.5°K is observed under hydrostatic pressure up to 14.7kbar. Direct evidence for an inversion of valence and conduction bands is obtained from the pressure coefficient measured on the same diode over the whole experimental range. We discuss briefly the nature of the band structure after the cross over point and suggest an explanation for an abrupt increase of the threshold current for laser action in these diodes at small gaps.     

Electric field distribution in the base of semiconductor <Emphasis Type="Italic">p-n</Emphasis> junction diode

An expression for distribution of the electric field in the base of a semiconductor p-n junction diode is obtained valid for arbitrary injection levels in the approximation of exponential distribution of non-equilibrium carriers in the diode base. It is shown that at a certain current the field is constant across the base which allows one to determine the mobility of majority carriers (whose concentration is determined from the barrier capacity measurements). For commercial D223B and D219A diodes the current-voltage characteristics and the differential resistance are measured and the mobility of electrons is calculated. The electric field distribution in the D223B diode is derived at three injection levels.     

窄线宽、高光束质量的外腔双反馈激光二极管阵列(英文)

设计了一种离轴双反馈外腔能够有效地改善激光二极管阵列的线宽和光束质量。闪耀光栅和高反镜之间形成了一个共振腔。通过调整光栅和高反镜之间的倾角可以选定一个空间模在共振腔中放大。将一个半波片插入外腔中的光栅反馈支路,来控制反馈光的数量,激光从光栅反馈支路输出。运用这项技术,在工作电流16 A,可以把激光二极管阵列的输出线宽压缩到0.15 nm,光束束宽积减小到283 mm.mrad。由于光栅的锁定作用,中心波长几乎不随温度的变化而改变。在工作电流17A时,输出激光的功率为2.44 W,斜率效率为0.5 W/A。     

High-efficiency, high-power, diode-pumped continuous-wave Tm:YAlO3 slab lasers

We report diode end-pumped continuous-wave Tm:YAlO₃ slab lasers with high power and high efficiency. At room temperature, b-cut Tm:YAlO₃ slabs with doping concentrations of 1, 4 and 5 at.% pumped by fiber-coupled and fast-axis collimated laser diodes with different wavelengths are compared. Tm:YAlO₃ slab lasers of 4 at.% doping concentrations have the highest optical-to-optical efficiency. When pumped with fiber-coupled and fast-axis collimated laser diodes, the maximum output powers are 11 W and 15 W, corresponding to a slope efficiency of 52% and 40%, respectively.     

Electroforming of thin film silicon based homojunction pin diode

The recent observations of bright visible electroluminescence (EL) from electroformed thin film silicon based wide-gap alloys are further clamped down in a simpler structure. For this purpose, a standard quality, ordinary hydrogenated amorphous silicon (a-Si:H) homojunction pin diode was fabricated by plasma enhanced chemical vapor deposition. The fresh diode was characterized by temperature scanned current–voltage (I–V) and constant photocurrent measurements. The energy distribution of density of states within the forbidden gap of the intrinsic a-Si:H layer was determined by space charge limited current and optical absorption spectroscopies. Then the diode was intentionally subjected to a sufficiently high, calibrated electric field leading to its Joule heating assisted rapid crystallization at ambient atmosphere. The fresh and the formed diodes exhibit different I–V and EL characteristics. The current density of the formed diode increases drastically at low voltages while remaining unchanged at high voltages when compared to that of the fresh diode. Parallelly, the room temperature EL intensity under a particular current stress is boosted with electroforming. These interesting phenomena have been discussed in the frame of a self-consistent model.     

A beam shaping design for coupling high power diode laser stack to fiber with capability of spectral narrowing and stabilizing

We applied a VHG-FAC lens in our design in this work to collimate the fast axis and lock the output spectrally. We used a beam shaping technique to improve the beam symmetry and power density of a high power diode laser stack with a stripe mirror plate, a V-Stack mirror and polarization beam combining elements. By this technique, the beam of a high power diode laser stack is effectively coupled into a standard 365 μmcore diameter and a NA = 0.22 fiber. By this technique, compactness, higher efficiency, narrower spectral line width and lower production cost of the diodes are possible.     

激光二极管侧抽运双棒串接准连续Nd∶YAG高功率绿光激光器

研制一台激光二极管(LD)侧面抽运双棒串接准连续Nd∶YAG折叠腔高功率绿光激光器,理论分析了热致双折射效应对系统的影响,并对用石英旋转片补偿前后的情况进行模拟对比。在考虑了补偿后的情况下设计了热稳定谐振腔。实验中采用两个串接的由30个20 W的LD阵列侧面抽运的Nd∶YAG棒和Ⅱ类临界相位匹配HGTR-KTP晶体,在抽运电流均为21.6 A,重复频率为27.2 kHz时,获得了最大平均输出功率为164 W,脉冲宽度为130 ns的532 nm绿光输出,光-光转换效率为13.7%,测得光束质量因子为M2x=9.52, M2y=9.86,不稳定度为2.3％。实验结果显示,经补偿后的激光系统能在宽的稳区范围内稳定运转。     

脉冲激光器大电流窄脉冲驱动设计

介绍了利用金属氧化物场效应管产生大电流窄脉冲来驱动激光二极管的原理,推导出驱动金属氧化物场效应管峰值驱动电流的计算公式和开通时间的估算公式,通过仿真总结出影响驱动电源脉冲电流的脉宽、幅度和振荡的主要因素,理论和仿真结果表明,器件的寄生电感、电路走线电感和负载寄生电感对电流影响较大。实验结果显示,在供电高压为200 V时,金属氧化物场效应管开通时间为2 ns;激光二极管驱动电流上升时间小于10 ns,脉宽为15~100 ns,幅度为0~50 A连续可调,频率为0~50 kHz。     

Efficient double-clad Yb3+-doped silica fibre laser pumped by an unfocused diode laser

A moderate output power Yb³⁺-doped double-clad fibre laser pumped by an unfocused diode laser is reported. This pumping configuration omits micro positioned lenses used in fibre coupled laser diodes, thus making the system significantly less complex and more robust. The maximum launch efficiency was ～80% and the maximum output power was >5 W with a measured FWHM of 18 pm.     

Two－Side Electron Beam Pumping System For Hundred－Joule－Level KrF Excimer Laser

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Active Phase-Shifting Interferometer Using Current Modulation of a Laser Diode

An active phase-shifting interferometer using current modulation of a laser diode is proposed. Fringe movement in the instrument is detected by a spatial filtering detector whose output is fed back to the injection current of the laser diode to lock the fringes and shift them correctly for phase shifting analysis. Frequency modulation characteristics of the laser diode and frequency response of the feedback system are first investigated. We constructed a portable interferometer head set apart from a mirror under test then measured the shape of a spherical mirror 130 mm in diameter, which was placed on a wooden table subject to vibration. Measurement repeatability of λ/35 was achieved.     

Frequency stabilization and output power undulations of diode lasers with feedback by volume holographic gratings

The mode-hop behavior and the power characteristics of a laser diode with wavelength-selective optical feedback are experimentally investigated. The feedback is provided by external volume holographic gratings, also called ‘Bragg mirrors’, at normal incidence. We demonstrate that a Bragg mirror forces a laser diode to operate only within a narrow wavelength range, and that the emission wavelength of the laser diode is stabilized against variations of the injection current. Moreover, we present periodic undulations of the power characteristics of the laser, depending on the driving current. They can be qualitatively explained with a simple model which takes into account that the threshold gain in the laser system strongly depends on the wavelength.     

Growth and properties of KLu(WO4)2, and novel ytterbium and thulium lasers based on this monoclinic crystalline host

High‐quality crystals of monoclinic KLu(WO₄)₂, shortly KLuW, were grown with sizes sufficient for its characterization and substantial progress was achieved in the field of spectroscopy and laser operation with Yb³⁺‐ and Tm³⁺‐doping. We review the growth methodology for bulk KLuW and epitaxial layers, its structural, thermo‐mechanical, and optical properties, the Yb³⁺ and Tm³⁺ spectroscopy, and present laser results obtained in several operational regimes both with Ti:sapphire and direct diode laser pumping using InGaAs and AlGaAs diodes near 980 and 800 nm, respectively. The slope efficiencies with respect to the absorbed pump power achieved with continuous‐wave (CW) bulk and epitaxial Yb:KLuW lasers under Ti:sapphire laser pumping were ≈ 57 and ≈ 66%, respectively. Output powers as high as 3.28 W were obtained with diode pumping in a simple two‐mirror cavity where the slope efficiency with respect to the incident pump power reached ≈ 78%. Passively Q‐switched laser operation of bulk Yb:KLuW was realized with a Cr:YAG saturable absorber resulting in oscillation at ≈ 1031 nm with a repetition rate of 28 kHz and simultaneous Raman conversion to ≈ 1138 nm with maximum energies of 32.4 and 14.4 μJ, respectively. The corresponding pulse durations were 1.41 and 0.71 ns. Passive mode‐locking by a semiconductor saturable absorber mirror (SESAM) produced bandwidth‐limited pulses with duration of 81 fs (1046 nm, 95 MHz) and 114 fs (1030 nm, 101 MHz) for bulk and epitaxial Yb:KLuW lasers, respectively. Slope efficiency as high as 69% with respect to the absorbed power and an output power of 4 W at 1950 nm were achieved with a diode‐pumped Tm:KLuW laser. The slope efficiency reached with an epitaxial Tm:KLuW laser under Ti:sapphire laser pumping was 64 %. The tunability achieved with bulk and epitaxial Tm:KLuW lasers extended from 1800 to 1987 nm and from 1894 to 2039 nm, respectively.     

Efficient mechanically Q-switched diode side pumped Nd:YAG laser using a rotating prism and mirror combination

In this paper the construction of a mechanically Q-switched diode side pumped Nd:YAG laser system is described. It consists of a 50 cm long plane-plane resonator Q-switched with a combination of a rotating prism and a mirror. With an optical to optical efficiency of 25% Q-switched pulses (@1064) of 48 mJ and 8 ns are obtained at a rep-rate of 30 Hz with an output in near TEMoo mode. At a peak power of 6 MW the M ² value is found to be 1.92. The laser is frequency doubled and then tested on a 50 ??m thick tantalum foil which results in circular holes of diameter 13 ??m in it.