M. Hemenway

High reliability of high power and high brightness diode lasers

We report on continued progress in the development of high power and high brightness single emitter laser diodes from 790 nm to 980 nm for reliable use in industrial and pumping applications. High performance has been demonstrated in nLIGHT’s diode laser technology in this spectral range with corresponding peak electrical-to-optical power conversion efficiency of ~65%. These pumps have been incorporated into nLIGHT’s fiber-coupled pump module, elementTM. We report the latest updates on performance and reliability of chips and fiber-coupled modules. This paper also includes a new chip design with significantly narrower slow-axis divergence which enables further improved reliable power and brightness. Preliminary reliability assessment data for these devices will be presented here as well.

High brightness fiber coupled pump modules optimized for optical efficiency and power

We report on the continued development of high performance fiber coupled laser diode modules at nLIGHT. We show that by optimizing the laser resonator design single emitter diode lasers can be tailored for high brightness or for reduced

Advances in high-brightness fiber-coupled laser modules for pumping multi-kW CW fiber lasers

/W applications. For instance, a fiber laser pump module based on 6 single emitter diode lasers couples efficiently into a 105 μm, 0.15 NA fiber with peak operating efficiency <59% and output power < 65W. These results are made possible by optimizing the diode laser slow axis brilliance and by increasing the optical to optical efficiency to 90%. We will also report on the development of tailored laser resonator that meets the power, brightness, and cost targets for industrial applications. For instance, a wider emitter has reliable performance of <18W of output power while maintaining the slow axis divergence required for coupling into a fiber with a 12 mm-mrad beam parameter product. The corresponding 50% increase in output power significantly improves the

High-power fiber-coupled diode lasers with superior brightness, efficiency, and reliability

/W performance. These results of high brightness and high efficiency demonstrate the pump technology required for next generation solid state, fiber lasers, and materials processing applications.

High-temperature diode laser pumps for low SWaP directed energy lasers (Conference Presentation)

High-power continuous wave (CW) fiber lasers with excellent beam quality continue to drive demand for higher brightness pump modules at 920 nm and 976 nm. Over the last decade, the brightness requirement for pumping state-of-the-art CW fiber lasers (CWFLs) has risen from approximately 0.5 W/(mm-mR)2 to ~2 W/(mm-mR)2 for today’s mutlikW CWFLs. The most advanced CWFLs demand even higher brightness pump modules in order to minimize design complexity, maximize efficiency, and maximize the stimulated Raman scattering threshold. This need has resulted in a reoptimization of the nLIGHT elementTM line to enable a commercial 200 W, 18-emitter package with a 0.15 NA beam in a 105 μm fiber, corresponding to a brightness of 3.2 W/(mm-mR)2 and a 25 % increase in power over the existing elementTM e14 at 155 W. Furthermore, we have demonstrated the further scalability of this reoptimized design with our next generation COS, resulting in a maximum of 272 W into 105 μm fiber with a brightness of 3.8 W/(mm-mR)2.

Continued improvement in reduced-mode (REM) diodes enable 272 W from 105 μm 0.15 NA beam

Advances in high performance fiber coupled diode lasers continue to enable new applications as well as strengthen existing uses through progressive improvements in power and brightness [1]. These improvements are most notable in multi-kW direct diode systems and kW fiber laser platforms that effectively transform better beam quality into superior system performance and in DPSS (Diode pumped solid state) application striving to scale TEM00 (fundamental transverse mode) power. We report on our recent single-emitter based fiber-coupled product platform, the elementTM, that addressed these applications at 8xx/9xx nm with optical powers over 200W in a range of fiber core sizes down to 105um and 0.14NA (Numerical Aperture). The product is a culmination of numerous packaging improvements: improving wall plug efficiencies (~50% electrical-to-optical) while improving volume manufacturability, enabling lower costs, improving usable chip brightness by, < 20% over previous generation chips, and increasing the reliable output power to 15W per chip. We additionally report on current developments to extend the power of the product platform to as high as 300W. This will be realized primarily through new chip architectures projected to further increase the useable chip brightness by an additional 20 % and correspondingly scaling reliable output powers. Second order improvements are proposed in packaging enhancements that capitalize on the increased chip power and brightness as well as expand the package’s thermal capabilities. Finally, an extended performance roadmap will translate expected power advances and increasing volumes into a projection of relative

Reduced-mode (REM) diodes enable high brightness fiber-coupled modules

/W decreases over the next several years.

Performance improvements to wavelength stabilized high power 885nm diode laser modules

Kilowatt-class fiber lasers and amplifiers are becoming increasingly important building blocks for power-scaling laser systems in various architectures for directed energy applications. Currently, state-of-the-art Yb-doped fiber lasers operating near 1060 nm operate with optical-to-optical power-conversion efficiency of about 66%. State-of-the-art fiber-coupled pump diodes near 975 nm operate with about 50% electrical-to-fiber-coupled optical power conversion efficiency at 25C heatsink temperature. Therefore, the total system electrical-to-optical power conversion efficiency is about 33%. As a result, a 50-kW fiber laser will generate 75 kW of heat at the pump module and 25 kW at the fiber laser module with a total waste heat of 100 kW. It is evident that three times as much waste heat is generated at the pump module. While improving the efficiency of the diodes primarily reduces the input power requirement, increasing the operating temperature primarily reduces the size and weight for thermal management systems. We will discuss improvement in diode laser design, thermal resistance of the package as well as improvement in fiber-coupled optical-to-optical efficiency to achieve high efficiency at higher operating temperature. These factors have a far-reaching implication in terms of significantly improving the overall SWAP requirements thus enabling DEW-class fiber lasers on airborne and other platforms.

High-brightness diodes and fiber-coupled modules

High-power, high-brightness diode lasers from 8xx nm to 9xx nm have been pursued in many applications including fiber laser pumping, materials processing, solid-state laser pumping, and consumer electronics manufacturing. In particular, 915 nm - 976 nm diodes are of interest as diode pumps for the kilowatt CW fiber lasers. Thus, there have been many technical efforts on driving the diode lasers to have both high power and high brightness to achieve high-performance and reduced manufacturing costs. This paper presents our continued progress in the development of high brightness fiber-coupled product platform, elementTM. In the past decade, the amount of power coupled into a single 105 μm and 0.15 NA fiber has increased by over a factor of ten through improved diode laser brilliance and the development of techniques for efficiently coupling multiple emitters into a single fiber. In this paper, we demonstrate the further brightness improvement and power-scaling enabled by both the rise in chip brightness/power and the increase in number of chips coupled into a given numerical aperture. We report a new x-REM design with brightness as high as 4.3 W/mm-mrad at a BPP of 3 mm-mrad. We also report the record 272W from a 2×9 elementTM with 105 μm/0.15 NA beam using x-REM diodes and a new product introduction at 200W output power from 105 μm/0.15 NA beam at 915 nm.

Reduced Mode Diodes for Increasing Laser Brightness

There is an increasing demand for high-power, high-brightness diode lasers from 8xx nm to 9xx nm for applications such as fiber laser pumping, materials processing, solid-state laser pumping, and consumer electronics manufacturing. The kilowatt CW fiber laser pumping (915 nm - 976 nm), in particular, requires the diode lasers to have both high power and high brightness in order to achieve high-performance and reduced manufacturing costs. This paper presents continued progress in the development of high brightness fiber-coupled product platform, elementTM. Further brightness improvement and power-scaling have been enabled by both the rise in chip brightness as well as the increase in number of chips used to couple into a given numerical aperture. We have developed a new generation of high power broad area laser known as reduced-mode diode (REM-diode) which suppresses many of the higher order modes in the slow axis and reduces divergence up to two times at the same operating conditions. To date, we have achieved slow-axis brightness as high as 4.3 W/mm-mrad for devices with thermal resistance of ~2.5 C/W. As a result, we have achieved >75 watts from a 1×6 elementTMin the 9xx nm spectral range; and 177 watts of peak power from a 2×6 elementTM. We have also improved our optics for fiber-coupling which accommodates 7 emitters per polarization in the same numerical aperture. Using this configuration, we project 200 watts of peak power from a 2×7 elementTM with a reliable product at 176 W of power from 105 μm and 0.15 NA fiber. REM-diodes can also be wavelength stabilized using VBGs. The reliability of REM-diodes are equal or better than broad area lasers (BALs). We present current status on ongoing reliability assessment of chip-on-submount.