Industrial lasers used for materials processing have become essential tools in a wide array of applications, including cutting, welding, drilling, cladding, marking, hardening, and additive manufacturing. The speed, quality, and process window are determined in part by the laser beam properties such as beam size, shape, and divergence. nLIGHT has developed a new multi-kilowatt fiber laser, Corona™, that provides rapid tunability of the beam characteristics directly from the laser output fiber using a novel, all-fiber mechanism. Programmable beam shapes include flat top and donut beams with beam diameters from 100 μm to 390 μm and beam parameter products from 3 to 20 mm-mrad (M2 values from 9 to 59). We describe the Corona fiber laser performance and show processing results and advantages of specific beam shapes for sheet-metal cutting, the largest industrial laser application.
Next-generation industrial fiber lasers enable challenging applications that cannot be addressed with legacy fiber lasers. Key features of next-generation fiber lasers include robust back-reflection protection, high power stability, wide power tunability, high-speed modulation and waveform generation, and facile field serviceability. These capabilities are enabled by high-performance components, particularly pump diodes and optical fibers, and by advanced fiber laser designs. We summarize the performance and reliability of nLIGHT diodes, fibers, and next-generation industrial fiber lasers at power levels of 500 W – 8 kW. We show back-reflection studies with up to 1 kW of back-reflected power, power-stability measurements in cw and modulated operation exhibiting sub-1% stability over a 5 – 100% power range, and high-speed modulation (100 kHz) and waveform generation with a bandwidth 20x higher than standard fiber lasers. We show results from representative applications, including cutting and welding of highly reflective metals (Cu and Al) for production of Li-ion battery modules and processing of carbon fiber reinforced polymers.
A new class of high power high brightness 808 nm QCW laser diode mini bars has been developed. With
nLight's nXLT facet passivation technology and improvements in epitaxial structure, mini bars of 3 mm
bar width with high efficiency design have tested to over 280 W peak power with peak efficiency over 64%
on conduction cooled CS packages, equivalent to output power density near 130 mW/μm. These mini laser
bars open up new applications as compact, portable, and low current pump sources.
Liftests have been carried out on conduction cooled CS packages and on QCW stacks. Over 370 million
(M) shots lifetest with high efficiency design has been demonstrated on CS so far without failure, and over
80 M shots on QCW stacks with accelerated stress lifetest have also proven high reliability on mini bars
with high temperature design. Failure analysis determined that the failure mechanism was related to bulk
defects, showing that mini laser bars are not prone to facet failure, which is consistent with the large current
pulse test and failure analysis on high power single emitters.
We report on recent progress in the control of optical modes toward the improvement of commercial high-performance
diode laser modules. Control of the transverse mode has allowed scaling of the optical mode volume, increasing the
peak output power of diode laser emitters by a factor of two. Commercially-available single emitter diodes operating at
885 nm now exhibit >25 W peak (12 W rated) at >60% conversion efficiency. In microchannel-cooled bar format, these
lasers operate >120 W at 62% conversion efficiency. Designs of similar performance operating at 976 nm have shown
>37,000 equivalent device hours with no failures. Advances in the control of lateral modes have enabled unprecedented
brightness scaling in a fiber-coupled package format. Leveraging scalable arrays of single emitters, the conductively-cooled
nLIGHT PearlTM package now delivers >80 W peak (50 W rated) at >53% conversion efficiency measured from
a 200-μm core fiber output and >45 W peak (35 W rated) at >52% conversion efficiency measured from a 100-μm fiber
output. nLIGHT has also expanded its product portfolio to include wavelength locking by means of external volume
Bragg gratings. By controlling the longitudinal modes of the laser, this technique is demonstrated to produce a narrow,
temperature-stabilized spectrum, with minimal performance degradation relative to similar free-running lasers.
A conductively cooled laser diode package design with hard AuSn solder and CTE matched sub mount is presented. We discuss how this platform eliminates the failure mechanisms associated with indium solder. We present the problem of catastrophic optical mirror damage (COMD) and show that nLight's nXLTTM facet passivation technology effectively eliminates facet defect initiated COMD as a failure mechanism for both single emitter and bar format laser diodes. By combining these technologies we have developed a product that has high reliability at high powers, even at increased operation temperatures. We present early results from on-going accelerated life testing of this configuration that suggests an 808nm, 30% fill factor device will have a MTTF of more than 21khrs at 60W CW, 25°C operating conditions and a MTTF of more than 6.4khrs when operated under hard pulsed (1 second on, 1 second off) conditions.