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.

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.

Peak CW optical power from single 1-cm diode laser bars is advancing rapidly across all commercial wavelengths and the available range of emission wavelengths also continues to increase. Both high efficiency similar to 50% and > 100-W power In P-based CW bars have been available in bar format around 1500-nm for some time, as required for eye-safe Illuminators and for pumping Er-YAG crystals. There is increasing demand for sources at longer wavelengths. Specifically, 1900-nm sources can be used to pump Holmium doped YAG crystals, to produce 2100-nm emission. Emission near 2100-nm is attractive for free-space communications and range-finding applications as the atmosphere has little absorption at this wavelength. Diode lasers that emit at 2100-nm could eliminate the need for the use of a solid-state laser system, at significant cost savings. 2100-nm sources can also be used as pump sources for Thulium doped solid-state crystals to reach even longer wavelengths. In addition, there are several promising medical applications including dental applications such as bone ablation and medical procedures such as opthamology. These long wavelength Sources are also key components in infra-red-counter-measure systems. We have extended our high performance 1500-nm material to longer wavelengths through optimization of design and epitaxial growth conditions and report peak CW Output powers from single 1-cm diode laser bars of 37W at 1910-nm and 25W at 2070-nm. 1-cm bars with 20% fill factor were tested under step-stress conditions Lip to 110-A per bar without failure, confirming reasonable robustness of this technology. Stacks Of Such bars deliver high powers in a collimated beam suitable for Pump applications. We demonstrate the natural spectral width of similar to 18nm of these laser bars can be reduced to < 3-nm with use of an external Volume Bragg Grating, as required for pump applications. We review the developments required to reach these powers, latest advances and prospects for longer wavelength, higher power and higher efficiency.

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 nXLT (TM) 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 degrees C operating conditions and a MTTF of more than 6.4khrs when operated under hard pulsed (1 second on, 1 second off) conditions.

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.

Focused development under the DARPA SHEDs program has lead to extremely high power conversion efficiency in the 9xx-nm wavelength band, leading to bars with efficiency in excess of 74%. We review progress in advancing efficiency and detail the route to > 85% at room temperature. The 9xx-nm wavelength band is commercially used for pumping Ytterbium-doped solid-state crystals and fiber lasers - only one of many diode laser markets. Fortunately, the lessons learned under SHEDs are transferable to other wavelengths. We report breakthrough efficiency results in the 8xx-nm band, for example showing 71% power conversion efficiency from 790-nm bars at powers > 100-W for CW and QCW packaging and testing. These wavelengths are required for pumping Neodymium-doped crystals, as used in the majority of fielded high power Diode Pumped Solid-State Laser systems. High efficiency is delivered using low voltage SHEDs designs, in combination with work to optimize the performance of the quantum well.

Peak optical power from single 1-cm diode laser bars is advancing rapidly across all commercial wavelengths. Progress to date has allowed us to demonstrate > 400-W peak output from single 1-cm diode laser bars at emission wavelengths from 800-nm to 980-nm. The available range of emission wavelengths has also been increased, with 90-W bars shown at 660-nm, 37W at 1910-nm and 25W at 2070-nm, complementing the 100-W bar previously demonstrated at 1470-nm. Peak power is seen to correlate closely peak power conversion efficiency. Further advances in diode laser efficiency and low thermal resistance packaging technology continue to drive these powers higher. The most critical improvements have been the reduction in the diode laser operating voltage through optimization of hetero-barriers (leading to 74% efficient 100-W bars on micro-channel at 975-nm) and a reduction in packaging thermal resistance by optimizing microchannel performance (leading to < 0.2-degrees C/W thermal resistance). We have also recently extended our high efficiency designs to shorter wavelengths, now delivering over 70% efficiency at 790-nm. Ever-increasing power levels (projected to eventually exceed 1-kW per bar) reduce the cost in Euro per W of diode laser systems, enabling broader application in military, industrial and medical markets. In addition, increasing availability of high powers at new wavelengths is enabling many new applications.

Interest is rapidly growing in solid-state lasers emitting from 1500-nm to 2100-nm with applications in eye-safe range finding, LIDAR, infrared countermeasures, medicine, dentistry, and others. Traditionally, these solid-state lasers have been pumped by flash lamps or more recently, by semiconductor diode lasers. In the case of the latter, the diodes of choice have been those emitting below 1-mu m. The sub-micron class of semiconductor diode lasers is highly mature and has enjoyed recent rapid advances in power and efficiency. Unfortunately, the quantum defect generated when converting to the desired wavelengths results in large amounts of excess heat generation leading to costly and heavy, expensive cooling systems and performance problems related to thermal lensing. System complexity adds further cost and weight when intermediaries, such as optical parametric oscillators, are required to reach the desired longer wavelengths. Recent advances in laser diodes emitting from 1400-nm to over 1900-nm now enable the near resonant pumping of such solid state media as Er:YAG, Ho:YAG and Cr:ZnSe. Record results in the peak output power and electrical-to-optical conversion efficiency of diode lasers emitting around 1470-nm, 1700-nm and 1900-nm are presented here.

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 Pearl™ 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.