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.
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.
We demonstrate a robust, compact, low-cost, pulsed, linearly polarized, 1064 nm, Yb:fiber laser system capable of generating ~100 kW peak power pulses and >17 W average power at repetition rates of 80 – 285 kHz. The system employs a configurable microchip seed laser that provides nanosecond (~1.0 – 1.5 ns) pulse durations. The seed pulses are amplified in an all-fiber, polarization maintaining, large mode area (LMA) fiber amplifier optimized for high peak power operation. The LMA Yb:fiber amplifier enables near diffraction limited beam quality at 100 kW peak power. The seed laser, fiber amplifier, and beam delivery optics are packaged into an air-cooled laser head of 152×330×87 mm3 with pump power provided from a separate air-cooled laser controller. Due to the high peak power, high beam quality, spectral purity, and linearly polarized nature of the output beam, the laser is readily frequency doubled to 532 nm. Average 532 nm powers up to 7 W and peak powers exceeding 40 kW have been demonstrated. Potential for scaling to higher peak and average powers in both the green and infrared (IR) will be discussed. This laser system has been field tested and demonstrated in numerous materials processing applications in both the IR and green, including scribing and marking. We discuss recent results that demonstrate success in processing a diverse array of representative industrial samples.
We report on the progress of highly-reliable, high-efficiency 885-nm diode laser bar arrays. Conduction-cooled hardsoldered
bars rated to 60W and 57% conversion efficiency demonstrate >30,000 device hours under 1-sec on, 1-sec off
hard pulse conditions failure-free. Microchannel-cooled bars rated to 100W and 62% efficiency demonstrate >100,000
accelerated device hours failure-free. Integrated volume Bragg grating fast axis lenses provide wavelength stabilization
at low cost. Vertically stacked arrays (seven bars each) of such configuration are demonstrated with a 0.8 nm FWHM
spectral width and rated to 700W, 53% conversion efficiency.
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. nLight's 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.
Laser diode reliability depends on both power and spectral stability over time. This report examines cases in which both
corrosion and ionic deposition resulted in wavelength shifts from less than 1 nm to greater than 7 nm in 60 - 100W bars
on microchannel coolers. Both corrosion and deposition seemed to be exacerbated by frequent and/or lengthy periods of
stagnation in the DI water system. Analytical results including SEM images of FIB cross-sections illustrate deposits of
up to several microns thickness of dielectric (oxide) material, as well as voiding caused by corrosion of Ni-plating out
from under Au-plating through pinhole defects. Thermal modeling confirms the effect of such features on thermal
resistance, correlating to observed wavelength shifts. Actions taken to address these issues are discussed.
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.
Many micromachining operations, particularly in the electronics sector, utilize pulsed solid-state UV lasers. These processes demand high levels of stability, as the yield and quality relate directly to the repeatability of each laser pulse. Critical stability issues arise with single-pulse processes (e.g. repair), situations requiring bursts of pulses (e.g. drilling), and continuous pulsing applications (e.g. cutting). To realize optimal stability specific design choices must be made, certain transient problems must be solved, and pulse energy measurements must be standardized. Solid-state UV lasers originate as infrared lasers, and nonlinear optics converts the infrared to the UV. This conversion introduces instability. Performing the conversion within the infrared laser cavity suppresses the instability, relative to performing the conversion outside of the laser cavity. We explain this phenomenon. Ideally, a versatile and stable solid-state laser can generate pulses in many formats. Thermal effects tend to prevent this versatile ideal, resulting in transient problems (unstable pulse trains), or less than optimal performance when the laser is pulsing continuously. Many methods of measuring pulse energy exist. Each method can produce surprisingly different results. We compare various techniques, discuss their limitations, and suggest an easily implemented pulse energy stability measurement.
The trend in micro-machining lasers is toward greater average power and higher repetition rate, in order to increase throughput, with pulse energy and peak power held roughly constant, as determined by the small scale of the feature. At repetition rates beyond 500 kHz, conventional high-power Q-switched Nd lasers will reach fundamental limits. We demonstrated a fiber-based oscillator-amplifier architecture which produces pulse repetition rates in the 0.5 - 5 MHz range and pulse durations in the 0.5 - 1.5 nsec range. The oscillator is a compact (35 cm3 package) passively Q-switched Nd:YVO4 laser oscillating at a single frequency. By amplifying this laser in fiber, we demonstrated 10-W average power at the two wavelengths of 914 nm and 1064 nm. At 1064-nm, Yb-doped large mode area fiber will allow scaling of average power to over 100 Watts, with peak power of tens of kW, in a diffraction-limited beam. Excellent conversion will be possible to visible and UV using the robust nonlinear material LBO. By opening up a new range of repetition rates and pulse lengths, at IR, visible and UV wavelengths, in a high power design that has the packaging and efficiency advantages of fiber, new micro-machining applications may be enabled.