High-energy density beam processes for welding, including laser beam welding and electron beam welding, are essential processes in many industries and provide unique characteristics that are not available with other processes used for welding. More recently, these high-energy density beams have been used to great advantage for additive manufacturing. This review of the literature serves to provide an overview of the evolution of the laser and electron beam processes including the fundamental nature of the beam itself and how such a high-energy density beam has been applied for welding. The unique nature of each process regarding weld bead formation and penetration, and metallurgical considerations are covered in detail. In addition, the evolution of monitoring systems for both characterization and control of these beam processes is reviewed. Over 500 references have been cited in this comprehensive review that will allow the reader to both understand the current state-of-the-art and explore in more detail the fundamental concepts and practical applications of these processes.

A review of high energy density beam processes for welding and additive manufacturing applications

The industrial laser market has rapidly expanded over the past decade with the emergence of advanced high brightness solid state laser technology. Thin disk laser systems are important examples of these powerful tools enabling a range of high-end CW materials processing applications such as 2D sheet metal cutting and remote welding applications, and the rising demand for a range of demanding high-energy pulsed applications of high average power. Commercial applications with power in the range of 8 kW- 20 kW can be cost competitive using disk lasers in moderate volumes compared to more commoditized solid-state laser sources such as fiber lasers. Reduction in the cost structure of disk laser pump sources requires an increase in brightness, efficiency and power of diode lasers bars within. Here we show the development of thin disk laser pump modules from an original common cooler platform with ~180 W per laser bar to recently developed individually cooled laser bars each operating continuously over 300 W. We demonstrate pump modules utilizing these bars with total power of up to 2.4 kW at 940 nm. Cooling in such laser modules is provided by mounting laser bars on isolated laser coolers (ILASCO). The ILASCO cooler comprises a multi-layer structure of aluminum nitride and copper sheets that are designed to decouple the direct current path from the water cooling eliminate electro-corrosion and to maximize heat dissipation and match the thermal expansion of the diode laser bar. We demonstrate advances in the single quantum well InGaAs/AlGaAs laser epitaxy design and chip layout that enables high power operation at operating temperatures up to 80°C. We show increase in peak electro-optic efficiencies from 55% to over 60% at this temperature. With the application of advanced facet passivation technology, we demonstrate >35 khr reliable operation in the application through accelerated aging tests.

Advances in diode laser bar power and reliability for multi-kW disk laser pump sources

Realization of thermally-near-unstable resonator thin-disk laser and compensation of air wedge effect

High-power, efficient semiconductor laser bars are demanded in many applications including pumping solid-state lasers and fibers. A narrow beam divergence is essential for increasing coupling efficiency and realizing an overall simple, cost-effective system. In kilowatt-class laser bars with 4 mm resonator length containing multiple broad-area emitters (with stripe width varying within 90–1200 μm) that are fabricated using conventional processing techniques, a strong thermal lens is generated within the individual emitters during laser operation. The lensing effect becomes stronger with increasing operating power. This allows a large number of lateral modes to be guided within the resonator and contribute to the laser emission, consequently deteriorating the beam quality (i.e. leading to larger lateral beam divergence angle). An approach to reduce the lateral divergence of the bar by modifying the in-plane structure of the emitters is presented. Based on simulation results, multiple lateral emitter structures have been developed and measured in quasi-continuous wave mode at low and high heat conditions with thermal resistance of 0.02 K/W and 0.05 K/W, respectively, comparable to continuous-wave testing with advanced coolers. Experimental results show that the improved lateral structures lead to enhanced power-current performance and improved beam divergence. A reduction of around 20% (~2°) in the bar lateral beam divergence angle at 95% power content has been achieved in testing at 800 W, with a simultaneous 5%-points gain in conversion efficiency with the highest performance lateral emitter structure.

Tailored in-plane thermal profiles for narrower lateral far-field in kilowatt-class 9xx nm diode laser bars

Diode lasers are key sources of optical energy for industrial machine tools and continuous improvement in their performance is needed to support performance and cost scaling efforts. For example, disk lasers as used in laser tools for metal cutting are typically pumped in continuous wave (CW) mode by 1-cm wide diode laser bars with an operating wavelength around λ = 940 nm, and ongoing increases in optical power per bar P opt are needed. Specifically, power scaling is needed above the current CW commercial level of around P opt = 300 W per bar [1] . Bars with performance at P opt = 1 kW and above have been demonstrated in research studies for many years (e.g. [2] ), with most work focussing on bar optimization for pulsed operation (ns-ms) as recently reviewed in [3] .

Increased Conversion Efficiency at 800 W Continuous Wave Output From Single 1-cm Diode Laser Bars at 940 nm

The rapid growth of industrial laser market is driven by the advance of high power laser technology. These high power laser systems require ever more reliable laser sources with higher brightness and higher efficiency. In this report, experimental and simulation data for pump laser diode bars show that improvements in epitaxial design can result in an increase of peak wall plug efficiency from 56% to 59% whilst maintaining slow axis divergence <8.5° at currents up to 300 A.

Electro-optical efficiency and slow axis far-field improvement of high power laser diode bars using epitaxy structure optimization

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Advances in diode laser bar power and reliability for multi-kW disk laser pump sources

Electro-optical efficiency and slow axis far-field improvement of high power laser diode bars using epitaxy structure optimization