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.
High power 780-820 nm diode lasers have been developed for pumping and material processing systems. This paper
presents recent progress in the development of such devices for use in high performance industrial applications. A newly
released laser design in this wavelength range demonstrates thermally limited >25W CW power without catastrophic
optical mirror damage (COMD), with peak wallplug efficiency ~65%. Ongoing accelerated lifetesting projects a time to
5% failure of ~10 years at 5 and 8 W operating powers for 95 and 200 μm emitter widths, respectively. Preliminary
results indicate the presence and competition of a random and wear-out failure mode. Fiber-coupled modules based on
arrays of these devices support >100W reliable operation, with a high 56% peak efficiency (ex-fiber) and improved
brightness/reliability.
Performance, lifetest data, as well as failure modes from two different device structures will be discussed in this paper,
with emitting wavelengths from 780nm to 800nm. The first structure, designed for high temperature operation, has
demonstrated good reliability on various packages with output power up to 10W from a 200μm emitting area. The device
structure can be operated up to 60°C heatsink temperatures under CW conditions. Then a high efficiency structure is
shown with further improvement on operation power and reliability, for room temperature operation. With ongoing
lifetest at 12A and 50°C heatsink temperature, <1000 FIT has been achieved for 6.5W and 33°C operation, on both
designs. MTT10%F at 10W and 25°C operation is estimated to be more than 20,000 hours. Devices retain more than 20W
rollover power under CW conditions, when re-tested after several thousand hours of accelerated lifetest. Paths for
reliability improvement will also be discussed based on observed lifetest failure modes from these two structures.
We present kW QCW vertical and horizontal arrays composed of 200W bars (peak power) at 8xxnm wavelength. We
also present an unique Bar-on-Submount design using the electrically insulating submounts, which can provide a
platform for simple and flexible horizontal array construction. The p-n junction temperature of the arrays under QCW
operation is modeled with FEA software, as well as measured in this research. Updated reliability test results for these
kW arrays will be also reported. As the examples, we present the performance of the vertical arrays with > 57% Wall-Plug-Efficiency and the horizontal arrays with < 23 degree fast axis divergence (FWHM), both with 808nm wavelength.
The available wavelength for such arrays ranges from 780nm to beyond 1 um. Coherent also have the capability to
produce the array with wide and relatively uniform spectrum for athermal pumping of solid-state lasers, by integrating
diode lasers bars with different wavelength into single array.
Diode pumped frequency doubled Optically Pumped Semiconductor lasers (OPS), has proven to be a reliable source
of laser radiation in the blue and blue-green spectral range between 460 nm and 505 nm. One of the major
advantages of using semiconductors as gain medium is the possibility to tailor the wavelength of the semiconductor
material by means of band gap engineering. Here we report about new OPS material enabling the wavelength region
between 1090 nm and 1160 nm which allows the realization of frequency doubled lasers between 545 nm and 580
nm. Laser results up to several Watts in the yellow spectral range as well as efficiency and lifetime data will be
presented.
Optically pumped semiconductor lasers offer significant advantages with respect to all traditional diode-pumped solid
state lasers (including fiber lasers) in regards to wavelength flexibility, broad pump tolerance, efficient spectral and
spatial brightness conversion and high power scaling. In this talk we will describe our recent progress in the lab and
applying this technology to commercial systems. Results include diversified wavelengths from 460 to 570nm, power
scaling to >60W of CW 532nm, and the launch of a low cost 5W CW visible source for forensic applications.
Power-scaling of optically pumped semiconductor lasers (OPSL's) using a resonator with multiple OPS chips is
demonstrated. With a 3-chip cavity and intra-cavity second harmonic generation, we obtain 55W of TEM00 mode output
at 532 nm and 66 W in multi-transverse mode. In addition, we describe the design of a periodic dynamically stable
resonator that allows scaling to more than 4 chips and demonstrate that the output power scales with the number of chips
in the cavity.
We describe the performance and reliability of multi-bar diode stacks assembled with hard solder attachment of the laser
diode bar to the conduction-cooled package substrate. The primary stack package design is based on a modular platform
that makes use of common piece parts to incorporate anywhere from 2-7 bars, operating at peak powers of 80W/bar to
200W/bar. In assembling monolithic type diode stack packages, it is typical to use a soft solder material such as indium
for P-side bar attachment into the package. Due to its low melting point and low yield stress, indium can provide a solder
joint that transfers low stress to the laser bar. However, during CW and QCW operation, indium is prone to migration
that can cause device failure due to a number of well-known mechanisms. This shortcoming of soft-solder bar
attachment can limit the number of shots the stack delivers over its operating life. By replacing the soft solder typically
used for P-side attachment with a hard solder, it is possible to greatly reduce or eliminate certain failure modes, thereby
increasing the operating life of the part. We demonstrate lifetime of > 1E9 shots at 80 W/bar, 250 us/40 Hz pulses, and
50C package operating temperature.
We describe the performance and reliability of high power vertical diode stacks based on silicon monolithic microchannel
coolers (SiMMs) operating at >1000W/cm2 CW at 808 and 940nm. The monolithic nature of these stacks makes
them inherently robust and compact. Typical emitting dimensions for a 10-bar stack are ~8.8mm × 10mm with CW
output power up to 1.5kW. Originally developed at Lawrence Livermore National Laboratory and now actively being
developed for commercial applications at Coherent, this technology offers several advantages over current copper-based
micro-channel coolers. These devices do not require use of DI water, strict monitoring and control of the pH level,
careful control of the water velocity, or sealed cooling systems. The need for hydrostatic seals is also drastically reduced.
A typical ten bar stack requires only 2 o-ring seals, compared to 20 such seals for a similar stack using copper microchannel
cooling. Mature and readily available wet etching technology allows for cost effective batch fabrication of the
sub-mount structure while achieving repeatable high precision components based on photolithographic fabrication
processes.
We present the reliability of high-power laser diodes utilizing hard solder (AuSn) on a conduction-cooled package
(HCCP). We present results of 50 W hard-pulse operation at 8xx nm and demonstrate a reliability of MTTF > 27 khrs
(90% CL), which is an order of magnitude improvement over traditional packaging. We also present results at 9xx nm
with a reliability of MTTF >17 khrs (90% CL) at 75 W. We discuss finite element analysis (FEA) modeling and time
dependent temperature measurements combined with experimental life-test data to quantify true hard-pulse operation.
We also discuss FEA and measured stress profiles across laser bars comparing soft and hard solder packaging.
Lasers based on optically pumped semiconductors (OPS) offer unique capabilities in both wavelength tailoring and power scaling compared to traditional solid-state lasers. In particular, these lasers can be designed in wavelength to realize for instance 505nm, which enables excitation of two fluorescent dye chemistry sets originally established by 488 and 514 nm legacy argon lasers. Highly efficient intra cavity frequency doubling of an 1010nm OPS yields over 100 mW of output power at 505 nm. In this paper we will present a brief background on OPS technology. We will then discuss specifics of the 505 nm laser and present both performance and reliability data for this laser.
Manufacturers of Nd:YAG lasers continue to demand 808 nm pump sources that deliver ever lower operating costs (measured in $/kW-hour). Responding to this demand, Coherent has developed a new generation of high power, 808 nm laser bars. These lasers are most ideal for high power QCW applications, but also perform very well in CW pumping applications. The key to the improved power for QCW bars is increase in catastrophic optical damage (COD) threshold. Through a combination of advances in epitaxial structure design and coating technology after aging COD limit for new generation of bars has been increased by 40%. This allowed us to achieve reliable QCW operation at 270W of peak power. Life test results shows that lifetime of these bars at these conditions exceed 2e9 shots. We also developed similar structure optimized for CW operations. When mounted on micro-channel water cooled packages CW bars operate reliably at an output power of 150 W. Highest power conversion efficiency (PCE) for CW bars was more
then 55% with typical PCE value >50%.
Ongoing optimization of epitaxial design within Coherent device engineering has led to a family of high power-conversion-efficiency (PCE) products on conductively cooled packages (CCP) and fiber array packages (FAP). At a 25°C heat sink temperature, the PCE was measured at 71.5% with 75W CW output power on 30% fill-factor (FF) bars with passive cooling. At heat sink temperatures as high as 60°C the PCE of these bars is still maintained above 60%. Powered by such high efficiency 9xx nm diodes, Coherent FAP products have consistently exceeded 55% PCE up to 50W power levels, with 62% PCE demonstrated out of the fiber. High linear-power-density (LPD) operation of 100μm x 7-emitter bars at LPD = 80 mW/μm was also demonstrated. Bars with 7-emitter were measured up to 140W QCW power before catastrophic optical mirror damage (COMD) occurred, which corresponds to a COMD value of 200mW/μm or 2D facet power density of 29.4 MW/cm2. Leveraging these improvements has enabled high power FAPs with >90W CW from an 800μm-diameter fiber bundle. Extensive reliability testing has already accumulated 400,000 total real-time device hours at a variety of accelerated and non-accelerated operating conditions. A random failure rate <0.5% per kilo-hours and gradual degradation rate <0.4% per kilo-hours have been observed. For a 30% FF 50W CW 9xx nm bar, this equates to >30,000 hours of median lifetime at a 90% confidence level. More optimized 30% FF 9xx nm bars are under development for power outputs up to 80W CW with extrapolated median lifetimes greater than 20,000 hours.
Optically pumped semiconductor material is a complimentary gain medium for rare earth or transition metal doped crystals. The design of several compositions based on GaAs allows the realization of a wavelength range between 710nm and 1180nm. This can be diode pumped and frequency doubled to cover the near UV up to the yellow spectral range. The power is scaleable and we have realized several Watts at 488nm and 460nm. Experimental results will be presented and discussed as well as reliability data to show that this technology has ripened for industrial applications.
We discuss a compact RGB source with ouput power of several watts per color consisting of a red (638 nm) diode and OPS lasers with blue (460 nm) and green (530) nm output. Suitability for display applications is shown by replacing the lamp of a standard Rear Projection TV.
Solid-state-laser and fiber laser pumping, reprographics, medical and materials processing applications require high power, high-brightness bars and fiber-coupled arrays. Conductively cooled laser diode bars allow customers to simplify system design and reduce operational size, weight, and costs. We present results on next generation high brightness, high reliability bars and fiber-coupled arrays at 790-830 nm, 940 nm and 980 nm wavelengths. By using novel epitaxial structures, we have demonstrated highly reliable 808 nm, 30% fill-factor conductively cooled bars operating at 60W CW mode, corresponding to a linear power density (LPD) of 20 mW/μm. At 25°C, the bars have shown greater than 50% wall-plug-efficiency (WPE) when operating at 60W. Our novel approach has also reduced the fast-axis divergence FWHM from 31° to less than 24°. These bars have a 50% brightness improvement compared to our standard products with this geometry. At 980nm, we have demonstrated greater than 100W CW from 20% fill-factor conductively cooled bars, corresponding to a LPD of 50 mW/µm. At 25°C, the WPE for 976nm bars consistently peaks above 65% and remains greater than 60% at 100W. We coupled the beam output from those high-brightness bars into fiber-array-packages (“FAPs”), and we also achieved high-brightness and high-efficiency FAPs. We demonstrated 60W from a 600µm core-diameter fiber-bundle with a high WPE of 55%, and a low numerical aperture of 0.115. The brightness of such FAPs is four times higher than our standard high-power 40W FAP products at Coherent. Ongoing life test data suggests an extrapolated lifetime greater than 10,000 hours at 80W CW operating-condition based on 30%FF conductively cooled bar geometry.
The reliability of novel, electrically pumped, vertical cavity 980-nm InGaAs lasers is demonstrated through accelerated life testing (ALT). The ALT methodology is used to detect failure modes as well as to obtain failure statistics. The time-to-failure (TTF) distribution and acceleration model are determined from over 200 devices tested from multiple wafers and assembly lots to account for process variation. The failure mode observed was gradual power degradation, while all other laser diode characteristics, e.g., threshold current, operating current and wavelength, remained stable. Laser output power degraded linearly in t1/2, where t is the stress time. The acceleration model best fitting the data is Black's equation with thermal activation energy of 0.89 eV and current density coefficient of 2.9. Verification of the acceleration model was confirmed through life testing over 500 devices at field operating conditions. The high level of reliability demonstrated meets strict telecommunications requirements.
We describe design and performance of novel, electrically pumped, vertical compound cavity semiconductor lasers emitting at 980 nm. The laser combines a vertical cavity semiconductor laser with a partially reflecting output coupler and an external cavity for mode control. The concept is scalable and has been demonstrated in monolithic low power (few miliwatts) devices all the way to high power extended cavity devices which generate over 950 mW CW multimode power and 0.5 W CW power in a TEM00 mode, the latter with 90% coupling efficiency into a single mode telecommunication fiber. The concept has been applied to the development of uncooled lasers, mounted in TO-56 cans, capable of producing 50 to 100 mW of fiber-coupled power. We have also demonstrated the extended cavity lasers at wavelengths of 920 nm and 1064 nm. We present reliability data for the chips used in the extended cavity lasers.
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