High efficiency, high power 808nm laser array and stacked arrays optimized for elevated temperature operation

Operation of 808-nm laser diode pumping at elevated temperature is crucial to many applications. Reliable operation at high power is limited by high thermal load and low catastrophic optical mirror damage (COMD) threshold at elevated temperature range. We demonstrated high efficiency and high power operation at elevated temperature with high COMD power. These results were achieved through device design optimization such as growth conditions, doping profile, and materials composition of the quantum-well and other layers. Electrical-to-optical efficiency as high as 62% was obtained through lowered threshold current, lowered series resistance and increased slope efficiency. The performance of single broad-area laser diodes scales to that of high power single bars on water-cooled copper micro-channel heatsinks or eonductively-cooled CS heatsinks. No reduction in bar performance or significant spectral broadening is seen when these micro-channel coolers are assembled into 6-bar and 18-bar CW stacks for the h     

大功率半导体激光器阵列的封装技术

半导体激光器阵列的应用已基本覆盖了整个光电子领域，成为当今光电子科学的重要技术。本文介绍了半导体激光器阵列的发展及其应用。着重阐述了半导体激光器阵列的封装技术——热沉材料的选择及其结构优化、热沉与半导体激光器阵列之间的焊接技术、半导体激光器阵列的冷却技术、与光纤的耦合技术等。     

Triggering GaAs lock-on switches with laser diode arrays

Progress toward the triggering of high-power photoconductive semiconductor switches (PCSSs) with laser diode arrays, is reported. An 850-W optical pulse from a laser diode array was used to trigger a 1.5-cm-long switch that delivered 8.5 MW to a 38.3-Ω load. Using 166-W arrays, it was possible to trigger a 2.5-mm-long switch delivering 1.2 MW with 600-ps rise-times at pulse repetition frequencies of 1 kHz. These 2.5-mm-long switches survived 10⁵ pulses at 1.0 MW levels. In single-pulse operation, up to 600 A was switched with laser diode arrays. The goal is to switch up to 5 kA in a single-shot mode and up to 100 MW repetitively at up to 10 kHz. At electric fields below 3 kV/cm GaAs switches are activated by creation of one electron-hole pair per photon. This linear mode demands high laser power and, after the light pulse, the carriers recombine in nanoseconds. At higher electric fields GaAs acts as a light-activated Zener diode. The laser light generates carriers as before, but the field induces gain such that the amount of light required to trigger the switch is reduced by a factor of up to 500. The gain continues until the field across the sample drops to a material-dependent lock-on field. The gain in the switch allows for the use of laser diodes     

73% CW power conversion efficiency at 50 W from 970 nm diode laser bars

970 nm emitting diode laser bars of broad-waveguide design have been optimised for maximum power conversion efficiency (PCE). 73% PCE at 50 W CW output power is achieved from 20% fill-factor, 1 cm diode laser bars mounted on microchannel-cooled heatsinks. The improvement is mainly the result of an increase in injection efficiency via moderately low doping of the broad-waveguide core, and reductions in operating voltage via doping optimisation of the broad-waveguide structure.     

Investigations of transient thermal properties of conductively cooled diode laser arrays operating under quasicontinuous-wave conditions

Thermal properties of diode laser arrays not only affect electrical and optical characteristics, they can also become determining factors for long-term reliability of the devices. Here, we report on the investigations of transient thermal effects in high-power diode arrays operating under quasicontinuous-wave (QCW) conditions. A novel measurement setup for the transient junction temperature determination is proposed. We show the measurement results of conductively cooled diode laser arrays mounted on the conventional copper heat sink as well as on the thermal expansion matched CuW submount. The presented results allow evaluation of the thermal cycling experienced by the device during pulsed operation. In the following part, time-resolved wavelength and temperature variations within an array are presented. The guidance for heat sink material choice for high-power diode laser arrays designed for QCW operation is given.     

Coherent photon seeding of actively modelocked laser diodes with optical fibre cavities

A modified fibre cavity for obtaining single longitudinal laser diode mode operation in active modelocking is proposed. It has been shown that if a fusion spliced plane is incorporated inside the singlemode fibre cavity, the reflection from it can provide the feedback necessary for coherent photon seeding. 39.2 ps pulses with a spectral width of 0.14 nm have been generated.<>     

80 GHz silicon diamond-heatsink Impatt diodes

80 GHz band silicon d.d.r. Impatt diodes with diamond heatsinks were fabricated. An output power of 1014 mW at 77.70 GHz was obtained by liquid-nitrogen-cooled operation, which gives the highest pf2 product, and 726 mW at 73.35 GHz by room temperature operation. Small-signal diode impedance was calculated considering operating temperature.     

High power diode laser arrays

Recent progress in the development of high-power diode laser arrays for solid-state laser pumping is detailed. Advances in available wavelength, efficiency, temperature of operation, duty cycle of operation, and peak and average power levels or densities are described. A packaging architecture capable of addressing the broadest range of pump applications and designs in an economic manner is defined, and a range of such package designs is presented     

Output characteristics of diode pumped fiber ASE sources

High power amplified spontaneous emission (ASE) from multicore Nd:fibers pumped by laser diode arrays is investigated experimentally and theoretically. Particular examination is made of threshold conditions at which lasing occurs. A model is presented which describes output power for arbitrary end reflectors. Experimental measurements of lasing threshold reflectivity versus pump power are made and are shown to deviate from the usual laser threshold condition at high pump powers. It is demonstrated that feedback from Rayleigh backscattering can be sufficient to drive the ASE source above lasing threshold in certain configurations     

Analysis of the line broadening of diode-pumped solid-state lasers

The output parameters of the most effective system for pumping of solid-state lasers that is based on laser diode arrays are studied. The spatial profile of radiation of specific diode arrays and the differences in the radiation spectra of emitting elements are determined. It is demonstrated that the main reason for the generation of additional modes and the spectral broadening of laser radiation is related to thermal effects resulting from the spatial nonuniformity of radiation of the diode pumping system.     

Coherent amplification characteristics of a GaAs phased array

The coherent amplification properties of antireflective coated GaAs diodes are considered for application to a phased array amplification scheme. The developmemt and design characteristics of a ten-element array system are discussed. An experimental diode array possessing good electrical and spectral match among diodes and excellent thermal dissipation is shown to provide optical gains, for main master laser modes, of at least 13 dB per array diode after coating. Temporal and spatial coherence within a GaAs laser spot, approximately 35 µ wide, is found to be adequate for array amplification purposes. The effects of array amplification on an incident coherent beam are evaluated by comparing predicted fringe patterns with observed interference patterns. The coherence of the incident beam is shown to be preserved during the amplification process.     

Analysis of semiconductor laser arrays with high-intensityuniformity

It is shown that an array with a highly uniform intensity distribution can be constructed. This decreases the spatial hole burning and makes stable, high-power operation easier. An estimate of the remaining spatial hole burning is derived and it is shown how its effects can be compensated for. It is considered that laser arrays which operate in the fundamental mode even at high-power levels can be designed     

The supermode structure of phase-locked diode laser arrays with variable channel spacing

The supermode structure of index-guided, phase-locked arrays of diode lasers with nonuniform laser spacing is investigated theoretically. It is shown that in a variable spacing array, the super-mode field patterns can be significantly different from those of a uniform array. However, in a variable-spacing array withNelements, supermodes ν andN + 1 - nu(nu = 1, 2, ..., N)have similar near-field intensity patterns and modal gains, as in the case of uniform arrays. As a result, the discrimination between the fundamental (0° phase shift) and the highest order (180° phase shift) supermodes is small and depends sensitively on the amount of gain in the interchannel regions, as for uniform arrays. This may explain the inefficient supermode discrimination and the wide beams exhibited by variable-spacing diode laser arrays, in contrast to the strong discrimination and the narrow beams obtained with chirped (variable channel width) arrays structures.     

Pitchfork bifurcation polarization bistability in laser diodes withexternal cavities

A new pitchfork bifurcation polarization bistability in laser diodes with a two-armed polarization-selective external cavity is examined theoretically and experimentally. The rate-equation analysis taking into account gain saturation has been carried out using the model for a laser diode whose laser thresholds of the TE and the TM modes can be changed independently through the changing of their photon lifetimes. It is shown from the analysis that pitchfork bifurcation polarization bistability appears when the laser thresholds for both modes are very close to each other and the switching between two stable states is obtained by means of a photon lifetime changing or a coherent or incoherent light injection. In the experiment, a 1.3-μm InGaAsP laser diodes with a T-shaped polarization-selective external cavity mas used. A new type of polarization bistability was observed when one arm was blocked and then recoupled. The two stable states mere also switched by means of an optical injection. All-optical flip-flop operation has been successfully demonstrated by using both TE and TM trigger inputs     

Efficient laser diode side pumped neodymium glass slab laser

The authors report efficient pulse operation of an Nd:glass slab laser-side-pumped by laser diode arrays. 7.5 mJ output and a slope efficiency of 29% were obtained with 35 nJ pump energy at 0.8 μm in 200 μs pulses. The wide absorption band at 0.8 and low laser loss in this phosphate glass allow for efficient pump light absorption and straightforward scalability to high power. The authors demonstrate 22% optical efficiency in a long pulse, multimode diode pumped laser oscillator based on a phosphate laser glass, LHG-8, highly doped with Nd ₂O₃. The strong and wide absorption bands in such phosphate glasses allow efficient pumping while somewhat relaxing the expensive wavelength selection requirements for laser arrays compared with crystal line host materials. With such materials, smaller slab thickness or rod diameters that are feasible with Nd:YAG can be used in the side-pumping geometry     

Electrical interactions of a superlinear laser diode with its external circuit

Self-induced fluctuations in diode voltage and current are shown to accompany the random optical fluctuations exhibited by AlGaAs junction lasers with superlinear emission characteristics. As a result, resonant interactions between the laser diode and a passive external electrical circuit produce coherent oscillations in the optically emitted power. Analysis of the conditions under which these resonantly induced oscillations occur shows that the intrinsic laser instability is current, not voltage, sensitive. No evidence is found, however, for a resonant-like behavior intrinsic to the laser itself.     

Etched-mirror unstable-resonator semiconductor lasers

The operation and performance of the first etched-mirror high-loss (ray unstable) semiconductor diode lasers are reported and discussed. This is an alternate approach to conventional plane-parallel stripe geometry diode lasers or monolithic laser arrays for obtaining improved mode control and higher power.     

半导体激光器阵列的“Smile”效应对光束质量的影响

建立"Smile"效应条件下半导体激光阵列近、远场模型,将光纤近场扫描法与高斯光束传输理论相结合,从理论和实验上证明了"Smile"效应值的大小与分布形态共同决定半导体激光器阵列快轴方向实际输出光束质量,获得了不同"Smile"效应条件下半导体激光阵列快轴方向光束参数积Kf值。     

Stable operation range for laser diodes with an integrated passivecavity in the presence of external optical feedback

It is shown that a laser diode with an integrated passive cavity yields higher tolerable levels of feedback from distant reflections than an equivalent long solitary laser diode. To ensure this high tolerance for external feedback, the internal feedback level in the integrated passive cavity must be of the order of about 10%. Then the laser diode remains stable up to external feedback levels in excess of 1% even if the internal reflection phase is not carefully adjusted. External reflections from a cleaved fiber end are then not sufficient to drive the laser into coherence collapse, if realistic coupling efficiencies between laser diode and fiber are taken into account. The low feedback sensitivity is explained by the combination of the long effective length of the laser and a high relaxation resonance frequency. Therefore, quantum-well laser diodes with a long length and a high relaxation resonance frequency are likewise expected to exhibit low feedback sensitivity     

二极管激光器运行特性的研究

对输出功率为50W的激光二极管的运行特性进行了测试,研究了冷却水温对激光二极管输出功率的影响,以及工作电流和冷却水温对激光二极管中心波长漂移的影响,为二极管泵浦固体激光器的设计提供有益参考.