Kirk Price

High-brightness fiber-coupled pump laser development

We report on the continued development of high brightness laser diode modules at nLIGHT Photonics. These modules, based on nLIGHTs PearlTM product platform, demonstrate excellence in output power, brightness, wavelength stabilization, and long wavelength performance. This system, based on 14 single emitters, is designed to couple diode laser light into a 105 μm fiber at an excitation NA of under 0.14. We demonstrate over 100W of optical power at 9xx nm with a diode brightness exceeding 20 MW/cm2-str with an operating efficiency of approximately 50%. Additional results show over 70W of optical coupled at 8xx nm. Record brilliance at wavelengths 14xx nm and longer will also be demonstrated, with over 15 W of optical power with a beam quality of 7.5 mm-mrad. These results of high brightness, high efficiency, and wavelength stabilization demonstrate the pump technology required for next generation solid state and fiber lasers.

High-performance wavelength-locked diode lasers

Rapidly maturing industrial laser applications are placing ever-tighter constraints on spectral width and wavelength emission stability over varying operating temperatures of high power diode laser pump sources. For example, improved power scaling and efficiency can be achieved by pumping the narrow upper laser level of Nd:YAG solid state lasers at 885 nm and the 1532-nm absorption band of Er:YAG solid state lasers, though taking full advantage of these configurations requires wavelength-locked pump sources. nLight offers a wide variety of wavelength-locked diode products based on external volume grating optics technology. It is often believed that the use of external gratings to wavelength lock diode lasers leads to an unavoidable loss in power and efficiency. nLights design methodology is shown to eliminate the problem in our grating-locked diode laser products. These results are expected to enable improved performance in diode-pumped solid state and fiber laser systems.

KW-class industrial diode lasers comprised of single emitters

Direct semiconductor diode laser-based systems have emerged as the preferred tool to address a wide range of material processing, solid-state and fiber laser pumping, and various military applications. We present an architectural framework and prototype results for kW-class laser tools based on single emitters that addresses a range of output powers (500W to multiple kW) and beam parameter products (20 to 100 mm-mrad) in a system with an operating efficiency near 50%. nLIGHT uses a variety of building blocks for these systems: a 100W, 105um, 0.14 NA pump module at 9xx nm; a 600W, 30 mm-mrad single wavelength, single polarization building block source; and a 140 W 20 mm-mrad low-cost module. The building block is selected to realize the brightness and cost targets necessary for the application. We also show how efficiency and reliability can be engineered to minimize operating and service costs while maximizing system up-time. Additionally we show the flexibility of this system by demonstrating systems at 8xx, 9xx, and 15xx nm. Finally, we investigate the diode reliability, FIT rate requirements, and package impact on system reliability.

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

Reliability of high power/brightness diode lasers emitting from 790 to 980 nm

/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-brightness, fiber-coupled pump modules in fiber laser applications

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

This paper presents recent progress in the development of high power single emitter laser diodes from 790 nm to 980 nm for reliable use in industrial and pumping applications. High performance has been demonstrated on diode lasers from 790 nm to 980 nm, with corresponding peak efficiency ~65%. Reliability has been fully demonstrated on high power diode lasers of 3.8 mm laser cavity at 3 major wavelengths. We report on the correlation between photon-energy (wavelength) and device failure modes (reliability). A newly released laser design demonstrates diode lasers with 5.0 mm laser cavity at 915-980 nm and 790 nm, with efficiency that matches the values achieved with 3.8 mm cavity length. 915-980 nm single emitters with 5.0 mm laser cavity were especially designed for high power and high brightness applications and can be reliably operated at 12 W to 18 W. These pumps have been incorporated into nLIGHT’s newly developed fiber coupled pump module, elementTM. Ongoing highly accelerated diode life-tests have accumulated over 200,000 raw device hours, with extremely low failure rate observed to date. High reliability has also been demonstrated from multiple accelerated module-level lifetests.

Brightness scaling of diodes lasers and fiber coupled modules at 9xx nm

High-power, high-brightness, fiber-coupled pump modules enable high-performance industrial fiber lasers with simple system architectures, multi-kW output powers, excellent beam quality, unsurpassed reliability, and low initial and operating costs. We report commercially available (element™), single-emitter-based, 9xx nm pump sources with powers up to 130 W in a 105 μm fiber and 250 W in a 200 μm fiber. This combination of high power and high brightness translates into improved fiber laser performance, e.g., simultaneously achieving high nonlinear thresholds and excellent beam quality at kW power levels. Wavelength-stabilized, 976 nm versions of these pumps are available for applications requiring minimization of the gain-fiber length (e.g., generation of high-peak-power pulses). Recent prototypes have achieved output powers up to 300 W in a 200 μm fiber. Extensive environmental and life testing at both the chip and module level under accelerated and real-world operating conditions have demonstrated extremely high reliability, with innovative designs having eliminated package-induced-failure mechanisms. Finally, we report integrated Pump Modules that provide < 1.6 kW of fiber-coupled power conveniently formatted for fiber-laser pumping or direct-diode applications; these 19” rack-mountable, 2U units combine the outputs of up to 14 elements™ using fused-fiber combiners, and they include high-efficiency diode drivers and safety sensors.

Progress in commercial wavelength-stabilized high-brightness diode sources suitable for pumping Yb-doped fiber lasers

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

High brightness diode laser module development at nLIGHT Photonics

/W decreases over the next several years.