Scott R. Karlsen

100-W 105-μm 0.15NA fiber coupled laser diode module

We report on the development of a high brightness laser diode module capable of coupling over 100W of optical power into a 105 μm 0.15 NA fiber at 976 nm. This module, based on nLIGHTs Pearl product architecture, utilizes hard soldered single emitters packaged into a compact and passively-cooled package. In this system each diode is individually collimated in the fast and slow axes and free-space coupled into a single fiber. The high brightness module has an optical excitation under 0.13 NA, is virtually free of cladding modes, and has an electrical to optical efficiency greater than 40%. Additionally, this module is compatible with high power 7:1 fused fiber combiners, and initial experiments demonstrated 500W coupled into a 220 μm, 0.22 NA fiber. These modules address the need in the market for higher brightness diode lasers for pumping fiber lasers and direct material processing.

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.

Reliability of high power diode laser systems based on single emitters

Diode laser modules based on arrays of single emitters offer a number of advantages over bar-based solutions including enhanced reliability, higher brightness, and lower cost per bright watt. This approach has enabled a rapid proliferation of commercially available high-brightness fiber-coupled diode laser modules. Incorporating ever-greater numbers of emitters within a single module offers a direct path for power scaling while simultaneously maintaining high brightness and minimizing overall cost. While reports of long lifetimes for single emitter diode laser technology are widespread, the complex relationship between the standalone chip reliability and package-induced failure modes, as well as the impact of built-in redundancy offered by multiple emitters, are not often discussed. In this work, we present our approach to the modeling of fiber-coupled laser systems based on single-emitter laser diodes.

Stabilization of Lateral Mode Transients in High-Power Broad Area Semiconductor Lasers

In this work, the temporal fluctuations of lateral modes in high-power broad area semiconductor lasers are investigated in the time domain. Index guiding (in the form of etched holes) is introduced as a method of stabilizing and controlling the lateral modes. Spatial control of the lateral modes and subsequent reduction of filamentation / smoothing of the near-field profile has already been predicted and experimentally shown to improve the efficiency of broad area laser diodes. Here, the method is shown to also dampen temporal instabilities (transients) of the lateral modes.

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

We report on the performance of a 100 W, 105μm, 0.17 NA (filled) fiber-coupled module operating at 976 nm. Volume holographic (Bragg) gratings are used to stabilize the emission spectrum to a 0.2 nm linewidth and wavelengthtemperature coefficient below 0.01nm/°C with virtually no penalty to the operating power or efficiency of the device. The typical fiber coupling efficiency for this design is >90%, enabling a rated operating efficiency of ~50%, the highest reported for a 100W/105μm-class diode pump module (wavelength stabilized or otherwise).

High brightness diode laser module development at nLIGHT Photonics

We report on the development of ultra-high brightness laser diode modules at nLIGHT Photonics. This paper demonstrates a laser diode module capable of coupling over 100W at 976 nm into a 105 μm, 0.15 NA fiber with fiber coupling efficiency greater than 85%. The high brightness module has an optical excitation under 0.13 NA, is virtually free of cladding modes, and has been wavelength stabilized with the use of volume holographic gratings for narrow-band operation. Utilizing nLIGHTs Pearl product architecture, these modules are based on hard soldered single emitters packaged into a compact and passively-cooled package. These modules are designed to be compatible with high power 7:1 fused fiber combiners, enabling over 500W power coupled into a 220 μm, 0.22 NA fiber. These modules address the need in the market for high brightness and wavelength stabilized diode lasers for pumping fiber lasers and solid-state laser systems.

532-nm pumped PPLT OPOs at 1 and 33 kHz

We describe the wavelength tunability and conversion efficiency of 532-nm pulse pumped optical parametric oscillators (OPOs) using periodically pulsed lithium tantalate (PPLT). The OPOs reported here used PPLT crystal lengths of 1,2 and 4 cm with signal wavelengths between 660 and 950 nm. These OPOs were pumped with a pump pulse energy of 100 (mu) J at 1 kHz yielding internal slope efficiencies of almost 90 percent and pump depletions of over 70 percent. Average power scaling experiments were also performed with a pump pulse energy of 66 (mu) J at 33 kHz yielding internal slope efficiencies of 50 percent.